WebGL Specification

Version 1.0.3, 27 October 2014

Copyright © 2014 Khronos Group

Abstract

This specification describes an additional rendering context and support objects for the HTML 5 canvas element [CANVAS]. This context allows rendering using an API that conforms closely to the OpenGL ES 2.0 API.

Status of this document

Public discussion of this specification is welcome on the (archived) WebGL mailing list public_webgl@khronos.org (see instructions).

Table of contents

Introduction

WebGL™ is an immediate mode 3D rendering API designed for the web. It is derived from OpenGL® ES 2.0, and provides similar rendering functionality, but in an HTML context. WebGL is designed as a rendering context for the HTML Canvas element. The HTML Canvas provides a destination for programmatic rendering in web pages, and allows for performing that rendering using different rendering APIs. The only such interface described as part of the Canvas specification is the 2D canvas rendering context, CanvasRenderingContext2D. This document describes another such interface, WebGLRenderingContext, which presents the WebGL API. The immediate mode nature of the API is a divergence from most web APIs. Given the many use cases of 3D graphics, WebGL chooses the approach of providing flexible primitives that can be applied to any use case. Libraries can provide an API on top of WebGL that is more tailored to specific areas, thus adding a convenience layer to WebGL that can accelerate and simplify development. However, because of its OpenGL ES 2.0 heritage, it should be straightforward for developers familiar with modern desktop OpenGL or OpenGL ES 2.0 development to transition to WebGL development.

Conventions

Many functions described in this document contain links to OpenGL ES man pages. While every effort is made to make these pages match the OpenGL ES 2.0 specification [GLES20], they may contain errors. In the case of a contradiction, the OpenGL ES 2.0 specification is the final authority.

The remaining sections of this document are intended to be read in conjunction with the OpenGL ES 2.0 specification (2.0.25 at the time of this writing, available from the Khronos OpenGL ES API Registry). Unless otherwise specified, the behavior of each method is defined by the OpenGL ES 2.0 specification. This specification may diverge from OpenGL ES 2.0 in order to ensure interoperability or security, often defining areas that OpenGL ES 2.0 leaves implementation-defined. These differences are summarized in the Differences Between WebGL and OpenGL ES 2.0 section.

Context Creation and Drawing Buffer Presentation

Before using the WebGL API, the author must obtain a WebGLRenderingContext object for a given HTMLCanvasElement [CANVAS] as described below. This object is used to manage OpenGL state and render to the drawing buffer, which must be created at the time of context creation.

Context Creation

Each WebGLRenderingContext has an associated canvas, set upon creation, which is a canvas [CANVAS].

Each WebGLRenderingContext has context creation parameters, set upon creation, in a WebGLContextAttributes object.

Each WebGLRenderingContext has actual context parameters, set each time the drawing buffer is created, in a WebGLContextAttributes object.

Each WebGLRenderingContext has a webgl context lost flag, which is initially unset.

When the getContext() method of a canvas element is to return a new object for the contextId webgl [CANVASCONTEXTS], the user agent must perform the following steps:

Create a new WebGLRenderingContext object, context. Let context's canvas be the canvas the getContext() method is associated with. Create a new WebGLContextAttributes object, contextAttributes. If getContext() was invoked with a second argument, options, set the attributes of contextAttributes from those specified in options. Create a drawing buffer using the settings specified in contextAttributes, and associate the drawing buffer with context. If drawing buffer creation failed, perform the following steps: Fire a WebGL context creation error at canvas. Return null and terminate these steps. Set the attributes of contextAttributes based on the properties of the newly created drawing buffer. Set context's context creation parameters to contextAttributes. Return context.

The canvas context type 'experimental-webgl' has historically been used to provide access to WebGL implementations which are not yet complete or conformant.

If the user agent supports both the webgl and experimental-webgl canvas context types, they shall be treated as aliases. For example, if a call to getContext('webgl') successfully creates a WebGLRenderingContext, a subsequent call to getContext('experimental-webgl') shall return the same context object.

The drawing buffer into which the API calls are rendered shall be defined upon creation of the WebGLRenderingContext object. The following description defines how to create a drawing buffer.

The table below shows all the buffers which make up the drawing buffer, along with their minimum sizes and whether they are defined or not by default. The size of this drawing buffer shall be determined by the width and height attributes of the HTMLCanvasElement. The table below also shows the value to which these buffers shall be cleared when first created, when the size is changed, or after presentation when the preserveDrawingBuffer context creation attribute is false .

Buffer Clear value Minimum size Defined by default? Color (0, 0, 0, 0) 8 bits per component yes Depth 1.0 16 bit integer yes Stencil 0 8 bits no

If the requested width or height cannot be satisfied, either when the drawing buffer is first created or when the width and height attributes of the HTMLCanvasElement are changed, a drawing buffer with smaller dimensions shall be created. The dimensions actually used are implementation dependent and there is no guarantee that a buffer with the same aspect ratio will be created. The actual drawing buffer size can be obtained from the drawingBufferWidth and drawingBufferHeight attributes.

A WebGL implementation must not perform any automatic scaling of the size of the drawing buffer on high-definition displays. The context's drawingBufferWidth and drawingBufferHeight must match the canvas's width and height attributes as closely as possible, modulo implementation-dependent constraints.

The constraint above does not change the amount of space the canvas element consumes on the web page, even on a high-definition display. The canvas's intrinsic dimensions [CANVAS] equal the size of its coordinate space, with the numbers interpreted in CSS pixels, and CSS pixels are resolution-independent [CSS]. A WebGL application can achieve a 1:1 ratio between drawing buffer pixels and on-screen pixels on high-definition displays by examining properties like window.devicePixelRatio , scaling the canvas's width and height by that factor, and setting its CSS width and height to the original width and height. An application can simulate the effect of running on a higher-resolution display simply by scaling up the canvas's width and height properties.

The optional WebGLContextAttributes object may be used to change whether or not the buffers are defined. It can also be used to define whether the color buffer will include an alpha channel. If defined, the alpha channel is used by the HTML compositor to combine the color buffer with the rest of the page. The WebGLContextAttributes object is only used on the first call to getContext . No facility is provided to change the attributes of the drawing buffer after its creation.

The depth , stencil and antialias attributes, when set to true, are requests, not requirements. The WebGL implementation should make a best effort to honor them. When any of these attributes is set to false, however, the WebGL implementation must not provide the associated functionality. Combinations of attributes not supported by the WebGL implementation or graphics hardware shall not cause a failure to create a WebGLRenderingContext. The actual context parameters are set to the attributes of the created drawing buffer. The alpha , premultipliedAlpha and preserveDrawingBuffer attributes must be obeyed by the WebGL implementation.

WebGL presents its drawing buffer to the HTML page compositor immediately before a compositing operation, but only if at least one of the following has occurred since the previous compositing operation:

Context creation

Canvas resize

clear , drawArrays , or drawElements has been called while the drawing buffer is the currently bound framebuffer

Before the drawing buffer is presented for compositing the implementation shall ensure that all rendering operations have been flushed to the drawing buffer. By default, after compositing the contents of the drawing buffer shall be cleared to their default values, as shown in the table above.

This default behavior can be changed by setting the preserveDrawingBuffer attribute of the WebGLContextAttributes object. If this flag is true, the contents of the drawing buffer shall be preserved until the author either clears or overwrites them. If this flag is false, attempting to perform operations using this context as a source image after the rendering function has returned can lead to undefined behavior. This includes readPixels or toDataURL calls, or using this context as the source image of another context's texImage2D or drawImage call.

While it is sometimes desirable to preserve the drawing buffer, it can cause significant performance loss on some platforms. Whenever possible this flag should remain false and other techniques used. Techniques like synchronous drawing buffer access (e.g., calling readPixels or toDataURL in the same function that renders to the drawing buffer) can be used to get the contents of the drawing buffer. If the author needs to render to the same drawing buffer over a series of calls, a Framebuffer Object can be used. Implementations may optimize away the required implicit clear operation of the Drawing Buffer as long as a guarantee can be made that the author cannot gain access to buffer contents from another process. For instance, if the author performs an explicit clear then the implicit clear is not needed.

OpenGL manages a rectangular viewport as part of its state which defines the placement of the rendering results in the drawing buffer. Upon creation of WebGL context context, the viewport is initialized to a rectangle with origin at (0, 0) and width and height equal to (context.drawingBufferWidth, context.drawingBufferHeight).

A WebGL implementation shall not affect the state of the OpenGL viewport in response to resizing of the canvas element.

var canvas = document.getElementById('canvas1'); var gl = canvas.getContext('webgl'); canvas.width = newWidth; canvas.height = newHeight; gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight); Note that if a WebGL program does not contain logic to set the viewport, it will not properly handle the case where the canvas is resized. The following ECMAScript example illustrates how a WebGL program might resize the canvas programmatically.

Rationale: automatically setting the viewport will interfere with applications that set it manually. Applications are expected to use onresize handlers to respond to changes in size of the canvas and set the OpenGL viewport in turn.

The OpenGL API allows the application to modify the blending modes used during rendering, and for this reason allows control over how alpha values in the drawing buffer are interpreted; see the premultipliedAlpha parameter in the WebGLContextAttributes section.

The HTML Canvas APIs toDataURL and drawImage must respect the premultipliedAlpha context creation parameter. When toDataURL is called against a Canvas into which WebGL content is being rendered, then if the requested image format does not specify premultiplied alpha and the WebGL context has the premultipliedAlpha parameter set to true, then the pixel values must be de-multiplied; i.e., the color channels are divided by the alpha channel. Note that this operation is lossy.

Passing a WebGL-rendered Canvas to the drawImage method of CanvasRenderingContext2D may or may not need to modify the the rendered WebGL content during the drawing operation, depending on the premultiplication needs of the CanvasRenderingContext2D implementation.

When passing a WebGL-rendered Canvas to the texImage2D API, then depending on the setting of the premultipliedAlpha context creation parameter of the passed canvas and the UNPACK_PREMULTIPLY_ALPHA_WEBGL pixel store parameter of the destination WebGL context, the pixel data may need to be changed to or from premultiplied form.

WebGL Resources

OpenGL manages several types of resources as part of its state. These are identified by integer object names and are obtained from OpenGL by various creation calls. In contrast WebGL represents these resources as DOM objects. Each object is derived from the WebGLObject interface. Currently supported resources are: textures, buffers (i.e., VBOs), framebuffers, renderbuffers, shaders and programs. The WebGLRenderingContext interface has a method to create a WebGLObject subclass for each type. Data from the underlying graphics library are stored in these objects and are fully managed by them. The resources represented by these objects are guaranteed to exist as long as the object exists. Furthermore, the DOM object is guaranteed to exist as long as the author has an explicit valid reference to it or as long as it is bound by the underlying graphics library. When none of these conditions exist the user agent can, at any point, delete the object using the equivalent of a delete call (e.g., deleteTexture). If authors wish to control when the underlying resource is released then the delete call can be made explicitly.

Security

Resource Restrictions

WebGL resources such as textures and vertex buffer objects (VBOs) must always contain initialized data, even if they were created without initial user data values. Creating a resource without initial values is commonly used to reserve space for a texture or VBO, which is then modified using texSubImage or bufferSubData calls. If initial data is not provided to these calls, the WebGL implementation must initialize their contents to 0; depth renderbuffers must be cleared to the default 1.0 clear depth. This may require creating a zeroed temporary buffer the size of a requested VBO, so that it can be initialized correctly. All other forms of loading data into a texture or VBO involve either ArrayBuffers or DOM objects such as images, and are therefore already required to be initialized.

When WebGL resources are accessed by shaders through a call such as drawElements or drawArrays , the WebGL implementation must ensure that the shader cannot access either out of bounds or uninitialized data. See Enabled Vertex Attributes and Range Checking for restrictions which must be enforced by the WebGL implementation.

In order to prevent information leakage, WebGL disallows uploading as textures:

Image or video elements whose origin is not the same as the origin of the Document that contains the WebGLRenderingContext's canvas element

Canvas elements whose origin-clean flag is set to false

If the texImage2D or texSubImage2D method is called with otherwise correct arguments and an HTMLImageElement , HTMLVideoElement , or HTMLCanvasElement violating these restrictions, a SECURITY_ERR exception must be thrown.

WebGL necessarily imposes stronger restrictions on the use of cross-domain media than other APIs such as the 2D canvas rendering context, because shaders can be used to indirectly deduce the contents of textures which have been uploaded to the GPU. WebGL applications may utilize images and videos that come from other domains, with the cooperation of the server hosting the media, using Cross-Origin Resource Sharing [CORS]. In order to use such media, the application needs to explicitly request permission to do so, and the server needs to explicitly grant permission. Successful CORS-enabled fetches of image and video elements from other domains cause the origin of these elements to be set to that of the containing Document [HTML]. The following ECMAScript example demonstrates how to issue a CORS request for an image coming from another domain. The image is fetched from the server without any credentials, i.e., cookies. var gl = ...; var image = new Image(); // The onload handler should be set to a function which uploads the HTMLImageElement // using texImage2D or texSubImage2D. image.onload = ...; image.crossOrigin = "anonymous"; image.src = "http://other-domain.com/image.jpg"; Note that these rules imply that the origin-clean flag for a canvas rendered using WebGL will never be set to false. For more information on issuing CORS requests for image and video elements, consult: CORS settings attributes [HTML]

The img element [HTML]

element [HTML] Media elements [HTML]

A WebGL implementation must only accept shaders which conform to The OpenGL ES Shading Language, Version 1.00 [GLES20GLSL], and which do not exceed the minimum functionality mandated in Sections 4 and 5 of Appendix A. In particular:

A shader referencing state variables or functions that are available in other versions of GLSL, such as that found in versions of OpenGL for the desktop, must not be allowed to load.

for loops must conform to the structural constraints in Appendix A.

loops must conform to the structural constraints in Appendix A. while and do-while loops are disallowed, since they are optional in Appendix A.

and loops are disallowed, since they are optional in Appendix A. Appendix A mandates certain forms of indexing of arrays; for example, within fragment shaders, indexing is only mandated with a constant-index-expression (see [GLES20GLSL] for the definition of this term). In the WebGL API, only the forms of indexing mandated in Appendix A are supported.

In addition to the reserved identifiers in the aforementioned specification, identifiers starting with "webgl_" and "_webgl_" are reserved for use by WebGL. A shader which declares a function, variable, structure name, or structure field starting with these prefixes must not be allowed to load.

Defense Against Denial of Service

It is possible to create, either intentionally or unintentionally, combinations of shaders and geometry that take an undesirably long time to render. This issue is analogous to that of long-running scripts, for which user agents already have safeguards. However, long-running draw calls can cause loss of interactivity for the entire window system, not just the user agent. In the general case it is not possible to impose limits on the structure of incoming shaders to guard against this problem. Experimentation has shown that even very strict structural limits are insufficient to prevent long rendering times, and such limits would prevent shader authors from implementing common algorithms. User agents should implement safeguards to prevent excessively long rendering times and associated loss of interactivity. Suggested safeguards include: Splitting up draw calls with large numbers of elements into smaller draw calls.

Timing individual draw calls and forbidding further rendering from a page if a certain timeout is exceeded.

Using any watchdog facilities available at the user level, graphics API level, or operating system level to limit the duration of draw calls.

Separating the graphics rendering of the user agent into a distinct operating system process which can be terminated and restarted without losing application state. The supporting infrastructure at the OS and graphics API layer is expected to improve over time, which is why the exact nature of these safeguards is not specified.

Shaders must not be allowed to read or write array elements that lie outside the bounds of the array. This includes any variable of array type, as well as vector or matrix types such as vec3 or mat4 when accessed using array subscripting syntax. If detected during compilation, such accesses must generate an error and prevent the shader from compiling. Otherwise, at runtime they shall return zero or the value at any valid index of the same array.

See Supported GLSL Constructs for more information on restrictions which simplify static analysis of the array indexing operations in shaders.

DOM Interfaces

This section describes the interfaces and functionality added to the DOM to support runtime access to the functionality described above.

Types

The following types are used in all interfaces in the following section.

typedef unsigned long GLenum; typedef boolean GLboolean; typedef unsigned long GLbitfield; typedef byte GLbyte; /* 'byte' should be a signed 8 bit type. */ typedef short GLshort; typedef long GLint; typedef long GLsizei; typedef long long GLintptr; typedef long long GLsizeiptr; // Ideally the typedef below would use 'unsigned byte', but that doesn't currently exist in Web IDL. typedef octet GLubyte; /* 'octet' should be an unsigned 8 bit type. */ typedef unsigned short GLushort; typedef unsigned long GLuint; typedef unrestricted float GLfloat; typedef unrestricted float GLclampf;

The WebGLContextAttributes dictionary contains drawing surface attributes and is passed as the second parameter to getContext .

dictionary WebGLContextAttributes { GLboolean alpha = true; GLboolean depth = true; GLboolean stencil = false; GLboolean antialias = true; GLboolean premultipliedAlpha = true; GLboolean preserveDrawingBuffer = false; GLboolean preferLowPowerToHighPerformance = false; GLboolean failIfMajorPerformanceCaveat = false; };

Context creation parameters

The following list describes each attribute in the WebGLContextAttributes object and its use. The default value for each attribute is shown above. The default value is used either if no second parameter is passed to getContext , or if a user object is passed which has no attribute of the given name.

alpha If the value is true, the drawing buffer has an alpha channel for the purposes of performing OpenGL destination alpha operations and compositing with the page. If the value is false, no alpha buffer is available. depth If the value is true, the drawing buffer has a depth buffer of at least 16 bits. If the value is false, no depth buffer is available. stencil If the value is true, the drawing buffer has a stencil buffer of at least 8 bits. If the value is false, no stencil buffer is available. antialias If the value is true and the implementation supports antialiasing the drawing buffer will perform antialiasing using its choice of technique (multisample/supersample) and quality. If the value is false or the implementation does not support antialiasing, no antialiasing is performed. premultipliedAlpha If the value is true the page compositor will assume the drawing buffer contains colors with premultiplied alpha. If the value is false the page compositor will assume that colors in the drawing buffer are not premultiplied. This flag is ignored if the alpha flag is false. See Premultiplied Alpha for more information on the effects of the premultipliedAlpha flag. preserveDrawingBuffer If false, once the drawing buffer is presented as described in theDrawing Buffer section, the contents of the drawing buffer are cleared to their default values. All elements of the drawing buffer (color, depth and stencil) are cleared. If the value is true the buffers will not be cleared and will preserve their values until cleared or overwritten by the author. On some hardware setting the preserveDrawingBuffer flag to true can have significant performance implications. preferLowPowerToHighPerformance Provides a hint to the implementation suggesting that, if possible, it creates a context that optimizes for power consumption over performance. For example, on hardware that has more than one GPU, it may be the case that one of them is less powerful but also uses less power. An implementation may choose to, and may have to, ignore this hint. failIfMajorPerformanceCaveat If the value is true, context creation will fail if the implementation determines that the performance of the created WebGL context would be dramatically lower than that of a native application making equivalent OpenGL calls. This could happen for a number of reasons, including: An implementation might switch to a software rasterizer if the user's GPU driver is known to be unstable.

An implementation might require reading back the framebuffer from GPU memory to system memory before compositing it with the rest of the page, significantly reducing performance. Applications that don't require high performance should leave this parameter at its default value of false . Applications that require high performance may set this parameter to true , and if context creation fails then the application may prefer to use a fallback rendering path such as a 2D canvas context. Alternatively the application can retry WebGL context creation with this parameter set to false , with the knowledge that a reduced-fidelity rendering mode should be used to improve performance.

getContext . It assumes the presence of a canvas element named "canvas1" on the page. var canvas = document.getElementById('canvas1'); var context = canvas.getContext('webgl', { antialias: false, stencil: true }); Here is an ECMAScript example which passes a WebGLContextAttributes argument to. It assumes the presence of a canvas element named "canvas1" on the page.

WebGLObject

The WebGLObject interface is the parent interface for all GL objects.

Each WebGLObject has an flag, which is initially unset.

interface WebGLObject { };

WebGLBuffer

The WebGLBuffer interface represents an OpenGL Buffer Object. The underlying object is created as if by calling glGenBuffers (OpenGL ES 2.0 §2.9, man page) , bound as if by calling glBindBuffer (OpenGL ES 2.0 §2.9, man page) and destroyed as if by calling glDeleteBuffers (OpenGL ES 2.0 §2.9, man page) .

interface WebGLBuffer : WebGLObject { };

The WebGLFramebuffer interface represents an OpenGL Framebuffer Object. The underlying object is created as if by calling glGenFramebuffers (OpenGL ES 2.0 §4.4.1, man page) , bound as if by calling glBindFramebuffer (OpenGL ES 2.0 §4.4.1, man page) and destroyed as if by calling glDeleteFramebuffers (OpenGL ES 2.0 §4.4.1, man page) .

interface WebGLFramebuffer : WebGLObject { };

WebGLProgram

The WebGLProgram interface represents an OpenGL Program Object. The underlying object is created as if by calling glCreateProgram (OpenGL ES 2.0 §2.10.3, man page) , used as if by calling glUseProgram (OpenGL ES 2.0 §2.10.3, man page) and destroyed as if by calling glDeleteProgram (OpenGL ES 2.0 §2.10.3, man page) .

interface WebGLProgram : WebGLObject { };

WebGLRenderbuffer

The WebGLRenderbuffer interface represents an OpenGL Renderbuffer Object. The underlying object is created as if by calling glGenRenderbuffers (OpenGL ES 2.0 §4.4.3, man page) , bound as if by calling glBindRenderbuffer (OpenGL ES 2.0 §4.4.3, man page) and destroyed as if by calling glDeleteRenderbuffers (OpenGL ES 2.0 §4.4.3, man page) .

interface WebGLRenderbuffer : WebGLObject { };

WebGLShader

The WebGLShader interface represents an OpenGL Shader Object. The underlying object is created as if by calling glCreateShader (OpenGL ES 2.0 §2.10.1, man page) , attached to a Program as if by calling glAttachShader (OpenGL ES 2.0 §2.10.3, man page) and destroyed as if by calling glDeleteShader (OpenGL ES 2.0 §2.10.1, man page) .

interface WebGLShader : WebGLObject { };

WebGLTexture

The WebGLTexture interface represents an OpenGL Texture Object. The underlying object is created as if by calling glGenTextures (OpenGL ES 2.0 §3.7.13, man page) , bound as if by calling glBindTexture (OpenGL ES 2.0 §3.7.13, man page) and destroyed as if by calling glDeleteTextures (OpenGL ES 2.0 §3.7.13, man page) .

interface WebGLTexture : WebGLObject { };

WebGLUniformLocation

The WebGLUniformLocation interface represents the location of a uniform variable in a shader program.

interface WebGLUniformLocation { };

WebGLActiveInfo

The WebGLActiveInfo interface represents the information returned from the getActiveAttrib and getActiveUniform calls.

interface WebGLActiveInfo { readonly attribute GLint size; readonly attribute GLenum type; readonly attribute DOMString name; };

Attributes

The following attributes are available:

size of type GLint The size of the requested variable. type of type GLenum The data type of the requested variable. name of type DOMString The name of the requested variable.

WebGLShaderPrecisionFormat

The WebGLShaderPrecisionFormat interface represents the information returned from the getShaderPrecisionFormat call.

interface WebGLShaderPrecisionFormat { readonly attribute GLint rangeMin; readonly attribute GLint rangeMax; readonly attribute GLint precision; };

Attributes

The following attributes are available:

rangeMin of type GLint The base 2 log of the absolute value of the minimum value that can be represented. rangeMax of type GLint The base 2 log of the absolute value of the maximum value that can be represented. precision of type GLint The number of bits of precision that can be represented. For integer formats this value is always 0.

Vertex, index, texture, and other data is transferred to the WebGL implementation using the ArrayBuffer and views defined in the Typed Array specification [TYPEDARRAYS].

Typed Arrays support the creation of interleaved, heterogeneous vertex data; uploading of distinct blocks of data into a large vertex buffer object; and most other use cases required by OpenGL programs.

var numVertices = 100; // for example // Compute the size needed for the buffer, in bytes and floats var vertexSize = 3 * Float32Array.BYTES_PER_ELEMENT + 4 * Uint8Array.BYTES_PER_ELEMENT; var vertexSizeInFloats = vertexSize / Float32Array.BYTES_PER_ELEMENT; // Allocate the buffer var buf = new ArrayBuffer(numVertices * vertexSize); // Map this buffer to a Float32Array to access the positions var positionArray = new Float32Array(buf); // Map the same buffer to a Uint8Array to access the color var colorArray = new Uint8Array(buf); // Set up the initial offset of the vertices and colors within the buffer var positionIdx = 0; var colorIdx = 3 * Float32Array.BYTES_PER_ELEMENT; // Initialize the buffer for (var i = 0; i < numVertices; i++) { positionArray[positionIdx] = ...; positionArray[positionIdx + 1] = ...; positionArray[positionIdx + 2] = ...; colorArray[colorIdx] = ...; colorArray[colorIdx + 1] = ...; colorArray[colorIdx + 2] = ...; colorArray[colorIdx + 3] = ...; positionIdx += vertexSizeInFloats; colorIdx += vertexSize; } Here is an ECMAScript example showing access to the same ArrayBuffer using different types of typed arrays. In this case the buffer contains a floating point vertex position (x, y, z) followed by a color as 4 unsigned bytes (r, g, b, a).

The WebGLRenderingContext represents the API allowing OpenGL ES 2.0 style rendering into the canvas element.

Before performing the implementation of any method of the WebGLRenderingContext interface or any method of an interface returned by the getExtension method, the following steps must be performed:

If the [WebGLHandlesContextLoss] extended attribute appears on the called method, perform the implementation of the called method, return its result and terminate these steps. Let use default return value be false. If the webgl context lost flag is set, let use default return value be true. If any argument to the method is a WebGLObject with its invalidated flag set, generate an INVALID_OPERATION error and let use default return value be true. If use default return value is true, perform the following steps: If the return type of the called method is any or any nullable type, return null. Terminate this algorithm without calling the method implementation. Otherwise, perform the implementation of the called method and return its result.

See the context lost event for further details.

interface mixin WebGLRenderingContextBase { /* ClearBufferMask */ const GLenum DEPTH_BUFFER_BIT = 0x00000100; const GLenum STENCIL_BUFFER_BIT = 0x00000400; const GLenum COLOR_BUFFER_BIT = 0x00004000; /* BeginMode */ const GLenum POINTS = 0x0000; const GLenum LINES = 0x0001; const GLenum LINE_LOOP = 0x0002; const GLenum LINE_STRIP = 0x0003; const GLenum TRIANGLES = 0x0004; const GLenum TRIANGLE_STRIP = 0x0005; const GLenum TRIANGLE_FAN = 0x0006; /* AlphaFunction (not supported in ES20) */ /* NEVER */ /* LESS */ /* EQUAL */ /* LEQUAL */ /* GREATER */ /* NOTEQUAL */ /* GEQUAL */ /* ALWAYS */ /* BlendingFactorDest */ const GLenum ZERO = 0; const GLenum ONE = 1; const GLenum SRC_COLOR = 0x0300; const GLenum ONE_MINUS_SRC_COLOR = 0x0301; const GLenum SRC_ALPHA = 0x0302; const GLenum ONE_MINUS_SRC_ALPHA = 0x0303; const GLenum DST_ALPHA = 0x0304; const GLenum ONE_MINUS_DST_ALPHA = 0x0305; /* BlendingFactorSrc */ /* ZERO */ /* ONE */ const GLenum DST_COLOR = 0x0306; const GLenum ONE_MINUS_DST_COLOR = 0x0307; const GLenum SRC_ALPHA_SATURATE = 0x0308; /* SRC_ALPHA */ /* ONE_MINUS_SRC_ALPHA */ /* DST_ALPHA */ /* ONE_MINUS_DST_ALPHA */ /* BlendEquationSeparate */ const GLenum FUNC_ADD = 0x8006; const GLenum BLEND_EQUATION = 0x8009; const GLenum BLEND_EQUATION_RGB = 0x8009; /* same as BLEND_EQUATION */ const GLenum BLEND_EQUATION_ALPHA = 0x883D; /* BlendSubtract */ const GLenum FUNC_SUBTRACT = 0x800A; const GLenum FUNC_REVERSE_SUBTRACT = 0x800B; /* Separate Blend Functions */ const GLenum BLEND_DST_RGB = 0x80C8; const GLenum BLEND_SRC_RGB = 0x80C9; const GLenum BLEND_DST_ALPHA = 0x80CA; const GLenum BLEND_SRC_ALPHA = 0x80CB; const GLenum CONSTANT_COLOR = 0x8001; const GLenum ONE_MINUS_CONSTANT_COLOR = 0x8002; const GLenum CONSTANT_ALPHA = 0x8003; const GLenum ONE_MINUS_CONSTANT_ALPHA = 0x8004; const GLenum BLEND_COLOR = 0x8005; /* Buffer Objects */ const GLenum ARRAY_BUFFER = 0x8892; const GLenum ELEMENT_ARRAY_BUFFER = 0x8893; const GLenum ARRAY_BUFFER_BINDING = 0x8894; const GLenum ELEMENT_ARRAY_BUFFER_BINDING = 0x8895; const GLenum STREAM_DRAW = 0x88E0; const GLenum STATIC_DRAW = 0x88E4; const GLenum DYNAMIC_DRAW = 0x88E8; const GLenum BUFFER_SIZE = 0x8764; const GLenum BUFFER_USAGE = 0x8765; const GLenum CURRENT_VERTEX_ATTRIB = 0x8626; /* CullFaceMode */ const GLenum FRONT = 0x0404; const GLenum BACK = 0x0405; const GLenum FRONT_AND_BACK = 0x0408; /* DepthFunction */ /* NEVER */ /* LESS */ /* EQUAL */ /* LEQUAL */ /* GREATER */ /* NOTEQUAL */ /* GEQUAL */ /* ALWAYS */ /* EnableCap */ /* TEXTURE_2D */ const GLenum CULL_FACE = 0x0B44; const GLenum BLEND = 0x0BE2; const GLenum DITHER = 0x0BD0; const GLenum STENCIL_TEST = 0x0B90; const GLenum DEPTH_TEST = 0x0B71; const GLenum SCISSOR_TEST = 0x0C11; const GLenum POLYGON_OFFSET_FILL = 0x8037; const GLenum SAMPLE_ALPHA_TO_COVERAGE = 0x809E; const GLenum SAMPLE_COVERAGE = 0x80A0; /* ErrorCode */ const GLenum NO_ERROR = 0; const GLenum INVALID_ENUM = 0x0500; const GLenum INVALID_VALUE = 0x0501; const GLenum INVALID_OPERATION = 0x0502; const GLenum OUT_OF_MEMORY = 0x0505; /* FrontFaceDirection */ const GLenum CW = 0x0900; const GLenum CCW = 0x0901; /* GetPName */ const GLenum LINE_WIDTH = 0x0B21; const GLenum ALIASED_POINT_SIZE_RANGE = 0x846D; const GLenum ALIASED_LINE_WIDTH_RANGE = 0x846E; const GLenum CULL_FACE_MODE = 0x0B45; const GLenum FRONT_FACE = 0x0B46; const GLenum DEPTH_RANGE = 0x0B70; const GLenum DEPTH_WRITEMASK = 0x0B72; const GLenum DEPTH_CLEAR_VALUE = 0x0B73; const GLenum DEPTH_FUNC = 0x0B74; const GLenum STENCIL_CLEAR_VALUE = 0x0B91; const GLenum STENCIL_FUNC = 0x0B92; const GLenum STENCIL_FAIL = 0x0B94; const GLenum STENCIL_PASS_DEPTH_FAIL = 0x0B95; const GLenum STENCIL_PASS_DEPTH_PASS = 0x0B96; const GLenum STENCIL_REF = 0x0B97; const GLenum STENCIL_VALUE_MASK = 0x0B93; const GLenum STENCIL_WRITEMASK = 0x0B98; const GLenum STENCIL_BACK_FUNC = 0x8800; const GLenum STENCIL_BACK_FAIL = 0x8801; const GLenum STENCIL_BACK_PASS_DEPTH_FAIL = 0x8802; const GLenum STENCIL_BACK_PASS_DEPTH_PASS = 0x8803; const GLenum STENCIL_BACK_REF = 0x8CA3; const GLenum STENCIL_BACK_VALUE_MASK = 0x8CA4; const GLenum STENCIL_BACK_WRITEMASK = 0x8CA5; const GLenum VIEWPORT = 0x0BA2; const GLenum SCISSOR_BOX = 0x0C10; /* SCISSOR_TEST */ const GLenum COLOR_CLEAR_VALUE = 0x0C22; const GLenum COLOR_WRITEMASK = 0x0C23; const GLenum UNPACK_ALIGNMENT = 0x0CF5; const GLenum PACK_ALIGNMENT = 0x0D05; const GLenum MAX_TEXTURE_SIZE = 0x0D33; const GLenum MAX_VIEWPORT_DIMS = 0x0D3A; const GLenum SUBPIXEL_BITS = 0x0D50; const GLenum RED_BITS = 0x0D52; const GLenum GREEN_BITS = 0x0D53; const GLenum BLUE_BITS = 0x0D54; const GLenum ALPHA_BITS = 0x0D55; const GLenum DEPTH_BITS = 0x0D56; const GLenum STENCIL_BITS = 0x0D57; const GLenum POLYGON_OFFSET_UNITS = 0x2A00; /* POLYGON_OFFSET_FILL */ const GLenum POLYGON_OFFSET_FACTOR = 0x8038; const GLenum TEXTURE_BINDING_2D = 0x8069; const GLenum SAMPLE_BUFFERS = 0x80A8; const GLenum SAMPLES = 0x80A9; const GLenum SAMPLE_COVERAGE_VALUE = 0x80AA; const GLenum SAMPLE_COVERAGE_INVERT = 0x80AB; /* GetTextureParameter */ /* TEXTURE_MAG_FILTER */ /* TEXTURE_MIN_FILTER */ /* TEXTURE_WRAP_S */ /* TEXTURE_WRAP_T */ const GLenum COMPRESSED_TEXTURE_FORMATS = 0x86A3; /* HintMode */ const GLenum DONT_CARE = 0x1100; const GLenum FASTEST = 0x1101; const GLenum NICEST = 0x1102; /* HintTarget */ const GLenum GENERATE_MIPMAP_HINT = 0x8192; /* DataType */ const GLenum BYTE = 0x1400; const GLenum UNSIGNED_BYTE = 0x1401; const GLenum SHORT = 0x1402; const GLenum UNSIGNED_SHORT = 0x1403; const GLenum INT = 0x1404; const GLenum UNSIGNED_INT = 0x1405; const GLenum FLOAT = 0x1406; /* PixelFormat */ const GLenum DEPTH_COMPONENT = 0x1902; const GLenum ALPHA = 0x1906; const GLenum RGB = 0x1907; const GLenum RGBA = 0x1908; const GLenum LUMINANCE = 0x1909; const GLenum LUMINANCE_ALPHA = 0x190A; /* PixelType */ /* UNSIGNED_BYTE */ const GLenum UNSIGNED_SHORT_4_4_4_4 = 0x8033; const GLenum UNSIGNED_SHORT_5_5_5_1 = 0x8034; const GLenum UNSIGNED_SHORT_5_6_5 = 0x8363; /* Shaders */ const GLenum FRAGMENT_SHADER = 0x8B30; const GLenum VERTEX_SHADER = 0x8B31; const GLenum MAX_VERTEX_ATTRIBS = 0x8869; const GLenum MAX_VERTEX_UNIFORM_VECTORS = 0x8DFB; const GLenum MAX_VARYING_VECTORS = 0x8DFC; const GLenum MAX_COMBINED_TEXTURE_IMAGE_UNITS = 0x8B4D; const GLenum MAX_VERTEX_TEXTURE_IMAGE_UNITS = 0x8B4C; const GLenum MAX_TEXTURE_IMAGE_UNITS = 0x8872; const GLenum MAX_FRAGMENT_UNIFORM_VECTORS = 0x8DFD; const GLenum SHADER_TYPE = 0x8B4F; const GLenum DELETE_STATUS = 0x8B80; const GLenum LINK_STATUS = 0x8B82; const GLenum VALIDATE_STATUS = 0x8B83; const GLenum ATTACHED_SHADERS = 0x8B85; const GLenum ACTIVE_UNIFORMS = 0x8B86; const GLenum ACTIVE_ATTRIBUTES = 0x8B89; const GLenum SHADING_LANGUAGE_VERSION = 0x8B8C; const GLenum CURRENT_PROGRAM = 0x8B8D; /* StencilFunction */ const GLenum NEVER = 0x0200; const GLenum LESS = 0x0201; const GLenum EQUAL = 0x0202; const GLenum LEQUAL = 0x0203; const GLenum GREATER = 0x0204; const GLenum NOTEQUAL = 0x0205; const GLenum GEQUAL = 0x0206; const GLenum ALWAYS = 0x0207; /* StencilOp */ /* ZERO */ const GLenum KEEP = 0x1E00; const GLenum REPLACE = 0x1E01; const GLenum INCR = 0x1E02; const GLenum DECR = 0x1E03; const GLenum INVERT = 0x150A; const GLenum INCR_WRAP = 0x8507; const GLenum DECR_WRAP = 0x8508; /* StringName */ const GLenum VENDOR = 0x1F00; const GLenum RENDERER = 0x1F01; const GLenum VERSION = 0x1F02; /* TextureMagFilter */ const GLenum NEAREST = 0x2600; const GLenum LINEAR = 0x2601; /* TextureMinFilter */ /* NEAREST */ /* LINEAR */ const GLenum NEAREST_MIPMAP_NEAREST = 0x2700; const GLenum LINEAR_MIPMAP_NEAREST = 0x2701; const GLenum NEAREST_MIPMAP_LINEAR = 0x2702; const GLenum LINEAR_MIPMAP_LINEAR = 0x2703; /* TextureParameterName */ const GLenum TEXTURE_MAG_FILTER = 0x2800; const GLenum TEXTURE_MIN_FILTER = 0x2801; const GLenum TEXTURE_WRAP_S = 0x2802; const GLenum TEXTURE_WRAP_T = 0x2803; /* TextureTarget */ const GLenum TEXTURE_2D = 0x0DE1; const GLenum TEXTURE = 0x1702; const GLenum TEXTURE_CUBE_MAP = 0x8513; const GLenum TEXTURE_BINDING_CUBE_MAP = 0x8514; const GLenum TEXTURE_CUBE_MAP_POSITIVE_X = 0x8515; const GLenum TEXTURE_CUBE_MAP_NEGATIVE_X = 0x8516; const GLenum TEXTURE_CUBE_MAP_POSITIVE_Y = 0x8517; const GLenum TEXTURE_CUBE_MAP_NEGATIVE_Y = 0x8518; const GLenum TEXTURE_CUBE_MAP_POSITIVE_Z = 0x8519; const GLenum TEXTURE_CUBE_MAP_NEGATIVE_Z = 0x851A; const GLenum MAX_CUBE_MAP_TEXTURE_SIZE = 0x851C; /* TextureUnit */ const GLenum TEXTURE0 = 0x84C0; const GLenum TEXTURE1 = 0x84C1; const GLenum TEXTURE2 = 0x84C2; const GLenum TEXTURE3 = 0x84C3; const GLenum TEXTURE4 = 0x84C4; const GLenum TEXTURE5 = 0x84C5; const GLenum TEXTURE6 = 0x84C6; const GLenum TEXTURE7 = 0x84C7; const GLenum TEXTURE8 = 0x84C8; const GLenum TEXTURE9 = 0x84C9; const GLenum TEXTURE10 = 0x84CA; const GLenum TEXTURE11 = 0x84CB; const GLenum TEXTURE12 = 0x84CC; const GLenum TEXTURE13 = 0x84CD; const GLenum TEXTURE14 = 0x84CE; const GLenum TEXTURE15 = 0x84CF; const GLenum TEXTURE16 = 0x84D0; const GLenum TEXTURE17 = 0x84D1; const GLenum TEXTURE18 = 0x84D2; const GLenum TEXTURE19 = 0x84D3; const GLenum TEXTURE20 = 0x84D4; const GLenum TEXTURE21 = 0x84D5; const GLenum TEXTURE22 = 0x84D6; const GLenum TEXTURE23 = 0x84D7; const GLenum TEXTURE24 = 0x84D8; const GLenum TEXTURE25 = 0x84D9; const GLenum TEXTURE26 = 0x84DA; const GLenum TEXTURE27 = 0x84DB; const GLenum TEXTURE28 = 0x84DC; const GLenum TEXTURE29 = 0x84DD; const GLenum TEXTURE30 = 0x84DE; const GLenum TEXTURE31 = 0x84DF; const GLenum ACTIVE_TEXTURE = 0x84E0; /* TextureWrapMode */ const GLenum REPEAT = 0x2901; const GLenum CLAMP_TO_EDGE = 0x812F; const GLenum MIRRORED_REPEAT = 0x8370; /* Uniform Types */ const GLenum FLOAT_VEC2 = 0x8B50; const GLenum FLOAT_VEC3 = 0x8B51; const GLenum FLOAT_VEC4 = 0x8B52; const GLenum INT_VEC2 = 0x8B53; const GLenum INT_VEC3 = 0x8B54; const GLenum INT_VEC4 = 0x8B55; const GLenum BOOL = 0x8B56; const GLenum BOOL_VEC2 = 0x8B57; const GLenum BOOL_VEC3 = 0x8B58; const GLenum BOOL_VEC4 = 0x8B59; const GLenum FLOAT_MAT2 = 0x8B5A; const GLenum FLOAT_MAT3 = 0x8B5B; const GLenum FLOAT_MAT4 = 0x8B5C; const GLenum SAMPLER_2D = 0x8B5E; const GLenum SAMPLER_CUBE = 0x8B60; /* Vertex Arrays */ const GLenum VERTEX_ATTRIB_ARRAY_ENABLED = 0x8622; const GLenum VERTEX_ATTRIB_ARRAY_SIZE = 0x8623; const GLenum VERTEX_ATTRIB_ARRAY_STRIDE = 0x8624; const GLenum VERTEX_ATTRIB_ARRAY_TYPE = 0x8625; const GLenum VERTEX_ATTRIB_ARRAY_NORMALIZED = 0x886A; const GLenum VERTEX_ATTRIB_ARRAY_POINTER = 0x8645; const GLenum VERTEX_ATTRIB_ARRAY_BUFFER_BINDING = 0x889F; /* Read Format */ const GLenum IMPLEMENTATION_COLOR_READ_TYPE = 0x8B9A; const GLenum IMPLEMENTATION_COLOR_READ_FORMAT = 0x8B9B; /* Shader Source */ const GLenum COMPILE_STATUS = 0x8B81; /* Shader Precision-Specified Types */ const GLenum LOW_FLOAT = 0x8DF0; const GLenum MEDIUM_FLOAT = 0x8DF1; const GLenum HIGH_FLOAT = 0x8DF2; const GLenum LOW_INT = 0x8DF3; const GLenum MEDIUM_INT = 0x8DF4; const GLenum HIGH_INT = 0x8DF5; /* Framebuffer Object. */ const GLenum FRAMEBUFFER = 0x8D40; const GLenum RENDERBUFFER = 0x8D41; const GLenum RGBA4 = 0x8056; const GLenum RGB5_A1 = 0x8057; const GLenum RGB565 = 0x8D62; const GLenum DEPTH_COMPONENT16 = 0x81A5; const GLenum STENCIL_INDEX = 0x1901; const GLenum STENCIL_INDEX8 = 0x8D48; const GLenum DEPTH_STENCIL = 0x84F9; const GLenum RENDERBUFFER_WIDTH = 0x8D42; const GLenum RENDERBUFFER_HEIGHT = 0x8D43; const GLenum RENDERBUFFER_INTERNAL_FORMAT = 0x8D44; const GLenum RENDERBUFFER_RED_SIZE = 0x8D50; const GLenum RENDERBUFFER_GREEN_SIZE = 0x8D51; const GLenum RENDERBUFFER_BLUE_SIZE = 0x8D52; const GLenum RENDERBUFFER_ALPHA_SIZE = 0x8D53; const GLenum RENDERBUFFER_DEPTH_SIZE = 0x8D54; const GLenum RENDERBUFFER_STENCIL_SIZE = 0x8D55; const GLenum FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE = 0x8CD0; const GLenum FRAMEBUFFER_ATTACHMENT_OBJECT_NAME = 0x8CD1; const GLenum FRAMEBUFFER_ATTACHMENT_TEXTURE_LEVEL = 0x8CD2; const GLenum FRAMEBUFFER_ATTACHMENT_TEXTURE_CUBE_MAP_FACE = 0x8CD3; const GLenum COLOR_ATTACHMENT0 = 0x8CE0; const GLenum DEPTH_ATTACHMENT = 0x8D00; const GLenum STENCIL_ATTACHMENT = 0x8D20; const GLenum DEPTH_STENCIL_ATTACHMENT = 0x821A; const GLenum NONE = 0; const GLenum FRAMEBUFFER_COMPLETE = 0x8CD5; const GLenum FRAMEBUFFER_INCOMPLETE_ATTACHMENT = 0x8CD6; const GLenum FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT = 0x8CD7; const GLenum FRAMEBUFFER_INCOMPLETE_DIMENSIONS = 0x8CD9; const GLenum FRAMEBUFFER_UNSUPPORTED = 0x8CDD; const GLenum FRAMEBUFFER_BINDING = 0x8CA6; const GLenum RENDERBUFFER_BINDING = 0x8CA7; const GLenum MAX_RENDERBUFFER_SIZE = 0x84E8; const GLenum INVALID_FRAMEBUFFER_OPERATION = 0x0506; /* WebGL-specific enums */ const GLenum UNPACK_FLIP_Y_WEBGL = 0x9240; const GLenum UNPACK_PREMULTIPLY_ALPHA_WEBGL = 0x9241; const GLenum CONTEXT_LOST_WEBGL = 0x9242; const GLenum UNPACK_COLORSPACE_CONVERSION_WEBGL = 0x9243; const GLenum BROWSER_DEFAULT_WEBGL = 0x9244; readonly attribute HTMLCanvasElement canvas; readonly attribute GLsizei drawingBufferWidth; readonly attribute GLsizei drawingBufferHeight; [WebGLHandlesContextLoss] WebGLContextAttributes? getContextAttributes(); [WebGLHandlesContextLoss] boolean isContextLost(); sequence<DOMString>? getSupportedExtensions(); object? getExtension(DOMString name); void activeTexture(GLenum texture); void attachShader(WebGLProgram? program, WebGLShader? shader); void bindAttribLocation(WebGLProgram? program, GLuint index, DOMString name); void bindBuffer(GLenum target, WebGLBuffer? buffer); void bindFramebuffer(GLenum target, WebGLFramebuffer? framebuffer); void bindRenderbuffer(GLenum target, WebGLRenderbuffer? renderbuffer); void bindTexture(GLenum target, WebGLTexture? texture); void blendColor(GLclampf red, GLclampf green, GLclampf blue, GLclampf alpha); void blendEquation(GLenum mode); void blendEquationSeparate(GLenum modeRGB, GLenum modeAlpha); void blendFunc(GLenum sfactor, GLenum dfactor); void blendFuncSeparate(GLenum srcRGB, GLenum dstRGB, GLenum srcAlpha, GLenum dstAlpha); typedef (ArrayBuffer or ArrayBufferView) BufferDataSource; void bufferData(GLenum target, GLsizeiptr size, GLenum usage); void bufferData(GLenum target, BufferDataSource? data, GLenum usage); void bufferSubData(GLenum target, GLintptr offset, BufferDataSource? data); [WebGLHandlesContextLoss] GLenum checkFramebufferStatus(GLenum target); void clear(GLbitfield mask); void clearColor(GLclampf red, GLclampf green, GLclampf blue, GLclampf alpha); void clearDepth(GLclampf depth); void clearStencil(GLint s); void colorMask(GLboolean red, GLboolean green, GLboolean blue, GLboolean alpha); void compileShader(WebGLShader? shader); void compressedTexImage2D(GLenum target, GLint level, GLenum internalformat, GLsizei width, GLsizei height, GLint border, ArrayBufferView data); void compressedTexSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLsizei width, GLsizei height, GLenum format, ArrayBufferView data); void copyTexImage2D(GLenum target, GLint level, GLenum internalformat, GLint x, GLint y, GLsizei width, GLsizei height, GLint border); void copyTexSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLint x, GLint y, GLsizei width, GLsizei height); WebGLBuffer? createBuffer(); WebGLFramebuffer? createFramebuffer(); WebGLProgram? createProgram(); WebGLRenderbuffer? createRenderbuffer(); WebGLShader? createShader(GLenum type); WebGLTexture? createTexture(); void cullFace(GLenum mode); void deleteBuffer(WebGLBuffer? buffer); void deleteFramebuffer(WebGLFramebuffer? framebuffer); void deleteProgram(WebGLProgram? program); void deleteRenderbuffer(WebGLRenderbuffer? renderbuffer); void deleteShader(WebGLShader? shader); void deleteTexture(WebGLTexture? texture); void depthFunc(GLenum func); void depthMask(GLboolean flag); void depthRange(GLclampf zNear, GLclampf zFar); void detachShader(WebGLProgram? program, WebGLShader? shader); void disable(GLenum cap); void disableVertexAttribArray(GLuint index); void drawArrays(GLenum mode, GLint first, GLsizei count); void drawElements(GLenum mode, GLsizei count, GLenum type, GLintptr offset); void enable(GLenum cap); void enableVertexAttribArray(GLuint index); void finish(); void flush(); void framebufferRenderbuffer(GLenum target, GLenum attachment, GLenum renderbuffertarget, WebGLRenderbuffer? renderbuffer); void framebufferTexture2D(GLenum target, GLenum attachment, GLenum textarget, WebGLTexture? texture, GLint level); void frontFace(GLenum mode); void generateMipmap(GLenum target); WebGLActiveInfo? getActiveAttrib(WebGLProgram? program, GLuint index); WebGLActiveInfo? getActiveUniform(WebGLProgram? program, GLuint index); sequence<WebGLShader>? getAttachedShaders(WebGLProgram? program); [WebGLHandlesContextLoss] GLint getAttribLocation(WebGLProgram? program, DOMString name); any getBufferParameter(GLenum target, GLenum pname); any getParameter(GLenum pname); [WebGLHandlesContextLoss] GLenum getError(); any getFramebufferAttachmentParameter(GLenum target, GLenum attachment, GLenum pname); any getProgramParameter(WebGLProgram? program, GLenum pname); DOMString? getProgramInfoLog(WebGLProgram? program); any getRenderbufferParameter(GLenum target, GLenum pname); any getShaderParameter(WebGLShader? shader, GLenum pname); WebGLShaderPrecisionFormat? getShaderPrecisionFormat(GLenum shadertype, GLenum precisiontype); DOMString? getShaderInfoLog(WebGLShader? shader); DOMString? getShaderSource(WebGLShader? shader); any getTexParameter(GLenum target, GLenum pname); any getUniform(WebGLProgram? program, WebGLUniformLocation? location); WebGLUniformLocation? getUniformLocation(WebGLProgram? program, DOMString name); any getVertexAttrib(GLuint index, GLenum pname); [WebGLHandlesContextLoss] GLsizeiptr getVertexAttribOffset(GLuint index, GLenum pname); void hint(GLenum target, GLenum mode); [WebGLHandlesContextLoss] GLboolean isBuffer(WebGLBuffer? buffer); [WebGLHandlesContextLoss] GLboolean isEnabled(GLenum cap); [WebGLHandlesContextLoss] GLboolean isFramebuffer(WebGLFramebuffer? framebuffer); [WebGLHandlesContextLoss] GLboolean isProgram(WebGLProgram? program); [WebGLHandlesContextLoss] GLboolean isRenderbuffer(WebGLRenderbuffer? renderbuffer); [WebGLHandlesContextLoss] GLboolean isShader(WebGLShader? shader); [WebGLHandlesContextLoss] GLboolean isTexture(WebGLTexture? texture); void lineWidth(GLfloat width); void linkProgram(WebGLProgram? program); void pixelStorei(GLenum pname, GLint param); void polygonOffset(GLfloat factor, GLfloat units); void readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, ArrayBufferView? pixels); void renderbufferStorage(GLenum target, GLenum internalformat, GLsizei width, GLsizei height); void sampleCoverage(GLclampf value, GLboolean invert); void scissor(GLint x, GLint y, GLsizei width, GLsizei height); void shaderSource(WebGLShader? shader, DOMString source); void stencilFunc(GLenum func, GLint ref, GLuint mask); void stencilFuncSeparate(GLenum face, GLenum func, GLint ref, GLuint mask); void stencilMask(GLuint mask); void stencilMaskSeparate(GLenum face, GLuint mask); void stencilOp(GLenum fail, GLenum zfail, GLenum zpass); void stencilOpSeparate(GLenum face, GLenum fail, GLenum zfail, GLenum zpass); typedef (ImageData or HTMLImageElement or HTMLCanvasElement or HTMLVideoElement) TexImageSource; void texImage2D(GLenum target, GLint level, GLenum internalformat, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, ArrayBufferView? pixels); void texImage2D(GLenum target, GLint level, GLenum internalformat, GLenum format, GLenum type, TexImageSource? source); // May throw DOMException void texParameterf(GLenum target, GLenum pname, GLfloat param); void texParameteri(GLenum target, GLenum pname, GLint param); void texSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLsizei width, GLsizei height, GLenum format, GLenum type, ArrayBufferView? pixels); void texSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLenum format, GLenum type, TexImageSource? source); // May throw DOMException void uniform1f(WebGLUniformLocation? location, GLfloat x); void uniform1fv(WebGLUniformLocation? location, Float32Array v); void uniform1fv(WebGLUniformLocation? location, sequence<GLfloat> v); void uniform1i(WebGLUniformLocation? location, GLint x); void uniform1iv(WebGLUniformLocation? location, Int32Array v); void uniform1iv(WebGLUniformLocation? location, sequence<long> v); void uniform2f(WebGLUniformLocation? location, GLfloat x, GLfloat y); void uniform2fv(WebGLUniformLocation? location, Float32Array v); void uniform2fv(WebGLUniformLocation? location, sequence<GLfloat> v); void uniform2i(WebGLUniformLocation? location, GLint x, GLint y); void uniform2iv(WebGLUniformLocation? location, Int32Array v); void uniform2iv(WebGLUniformLocation? location, sequence<long> v); void uniform3f(WebGLUniformLocation? location, GLfloat x, GLfloat y, GLfloat z); void uniform3fv(WebGLUniformLocation? location, Float32Array v); void uniform3fv(WebGLUniformLocation? location, sequence<GLfloat> v); void uniform3i(WebGLUniformLocation? location, GLint x, GLint y, GLint z); void uniform3iv(WebGLUniformLocation? location, Int32Array v); void uniform3iv(WebGLUniformLocation? location, sequence<long> v); void uniform4f(WebGLUniformLocation? location, GLfloat x, GLfloat y, GLfloat z, GLfloat w); void uniform4fv(WebGLUniformLocation? location, Float32Array v); void uniform4fv(WebGLUniformLocation? location, sequence<GLfloat> v); void uniform4i(WebGLUniformLocation? location, GLint x, GLint y, GLint z, GLint w); void uniform4iv(WebGLUniformLocation? location, Int32Array v); void uniform4iv(WebGLUniformLocation? location, sequence<long> v); void uniformMatrix2fv(WebGLUniformLocation? location, GLboolean transpose, Float32Array value); void uniformMatrix2fv(WebGLUniformLocation? location, GLboolean transpose, sequence<GLfloat> value); void uniformMatrix3fv(WebGLUniformLocation? location, GLboolean transpose, Float32Array value); void uniformMatrix3fv(WebGLUniformLocation? location, GLboolean transpose, sequence<GLfloat> value); void uniformMatrix4fv(WebGLUniformLocation? location, GLboolean transpose, Float32Array value); void uniformMatrix4fv(WebGLUniformLocation? location, GLboolean transpose, sequence<GLfloat> value); void useProgram(WebGLProgram? program); void validateProgram(WebGLProgram? program); void vertexAttrib1f(GLuint indx, GLfloat x); void vertexAttrib1fv(GLuint indx, Float32Array values); void vertexAttrib1fv(GLuint indx, sequence<GLfloat> values); void vertexAttrib2f(GLuint indx, GLfloat x, GLfloat y); void vertexAttrib2fv(GLuint indx, Float32Array values); void vertexAttrib2fv(GLuint indx, sequence<GLfloat> values); void vertexAttrib3f(GLuint indx, GLfloat x, GLfloat y, GLfloat z); void vertexAttrib3fv(GLuint indx, Float32Array values); void vertexAttrib3fv(GLuint indx, sequence<GLfloat> values); void vertexAttrib4f(GLuint indx, GLfloat x, GLfloat y, GLfloat z, GLfloat w); void vertexAttrib4fv(GLuint indx, Float32Array values); void vertexAttrib4fv(GLuint indx, sequence<GLfloat> values); void vertexAttribPointer(GLuint indx, GLint size, GLenum type, GLboolean normalized, GLsizei stride, GLintptr offset); void viewport(GLint x, GLint y, GLsizei width, GLsizei height); }; interface WebGLRenderingContext { }; WebGLRenderingContext includes WebGLRenderingContextBase;

Attributes

The following attributes are available:

canvas of type HTMLCanvasElement A reference to the canvas element which created this context. drawingBufferWidth of type GLsizei The actual width of the drawing buffer. May be different from the width attribute of the HTMLCanvasElement if the implementation is unable to satisfy the requested widthor height. drawingBufferHeight of type GLsizei The actual height of the drawing buffer. May be different from the height attribute of the HTMLCanvasElement if the implementation is unable to satisfy the requested width or height.

Getting information about the context

[WebGLHandlesContextLoss] WebGLContextAttributes? getContextAttributes() If the webgl context lost flag is set, returns null. Otherwise, returns a copy of the actual context parameters.

Setting and getting state

OpenGL ES 2.0 maintains state values for use in rendering. All the calls in this group behave identically to their OpenGL counterparts unless otherwise noted.

Viewing and clipping

Drawing commands can only modify pixels inside the currently bound framebuffer. In addition, the viewport and the scissor box affect drawing.

The viewport specifies the affine transformation of x and y from normalized device coordinates to window coordinates. The size of the viewport is initially determined as specified in section The WebGL Viewport. The scissor box defines a rectangle which constrains drawing. When the scissor test is enabled only pixels that lie within the scissor box can be modified by drawing commands including clear , and primitives can only be drawn inside the intersection of the viewport, the currently bound framebuffer, and the scissor box. When the scissor test is not enabled primitives can only be drawn inside the intersection of the viewport and the currently bound framebuffer.

Buffer objects

Buffer objects (sometimes referred to as VBOs) hold vertex attribute data for the GLSL shaders.

Framebuffer objects

Framebuffer objects provide an alternative rendering target to the drawing buffer. They are a collection of color, alpha, depth and stencil buffers and are often used to render an image that will later be used as a texture.

Renderbuffer objects

Renderbuffer objects are used to provide storage for the individual buffers used in a framebuffer object.

Texture objects

Texture objects provide storage and state for texturing operations. If no WebGLTexture is bound (e.g., passing null or 0 to bindTexture) then attempts to modify or query the texture object shall generate an INVALID_OPERATION error. This is indicated in the functions below.

Programs and Shaders

Rendering with OpenGL ES 2.0 requires the use of shaders, written in OpenGL ES's shading language, GLSL ES. Shaders must be loaded with a source string (shaderSource), compiled (compileShader) and attached to a program (attachShader) which must be linked (linkProgram) and then used (useProgram).

Uniforms and attributes

Values used by the shaders are passed in as uniforms or vertex attributes.

OpenGL ES 2.0 has 3 calls which can render to the drawing buffer: clear , drawArrays and drawElements . Furthermore rendering can be directed to the drawing buffer or to a Framebuffer object. When rendering is directed to the drawing buffer, making any of the 3 rendering calls shall cause the drawing buffer to be presented to the HTML page compositor at the start of the next compositing operation.

Pixels in the current framebuffer can be read back into an ArrayBufferView object.

void readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, ArrayBufferView? pixels) OpenGL ES 2.0 §4.3.1, man page) Fills pixels with the pixel data in the specified rectangle of the frame buffer. The data returned from readPixels must be up-to-date as of the most recently sent drawing command.



The type of pixels must match the type of the data to be read. For example, if it is UNSIGNED_BYTE, a Uint8Array must be supplied; if it is UNSIGNED_SHORT_5_6_5, UNSIGNED_SHORT_4_4_4_4, or UNSIGNED_SHORT_5_5_5_1, a Uint16Array must be supplied. If the types do not match, an INVALID_OPERATION error is generated.



Only two combinations of format and type are accepted. The first is format RGBA and type UNSIGNED_BYTE. The second is an implementation-chosen format. The values of format and type for this format may be determined by calling getParameter with the symbolic constants IMPLEMENTATION_COLOR_READ_FORMAT and IMPLEMENTATION_COLOR_READ_TYPE, respectively. The implementation-chosen format may vary depending on the format of the currently bound rendering surface. Unsupported combinations of format and type will generate an INVALID_OPERATION error.



If pixels is null, an INVALID_VALUE error is generated. If pixels is non-null, but is not large enough to retrieve all of the pixels in the specified rectangle taking into account pixel store modes, an INVALID_OPERATION error is generated.



For any pixel lying outside the frame buffer, the value read contains 0 in all channels; see Reading Pixels Outside the Framebuffer.



If this function attempts to read from a complete framebuffer with a missing color attachment, an INVALID_OPERATION error is generated per Reading from a Missing Attachment.

Detecting context lost events

Occurrences such as power events on mobile devices may cause the WebGL rendering context to be lost at any time and require the application to rebuild it; see WebGLContextEvent for more details. The following method assists in detecting context lost events.

[WebGLHandlesContextLoss] boolean isContextLost() Return true if the webgl context lost flag is set, otherwise return false.

Detecting and enabling extensions

An implementation of WebGL must not support any additional parameters, constants or functions without first enabling that functionality through the extension mechanism. The getSupportedExtensions function returns an array of the extension strings supported by this implementation. An extension is enabled by passing one of those strings to the getExtension function. This call returns an object which contains any constants or functions defined by that extension. The definition of that object is specific to the extension and must be defined by the extension specification.

Once an extension is enabled, it is only disabled if the WebGL rendering context is lost (see below), with the exception of the "WEBGL_lose_context" extension which remains active through any loss of context. Any objects referenced by a disabled extension, such as the object returned by getExtension , are no longer associated with the WebGL rendering context. Any extension objects that derive from WebGLObject have their invalidated flag set to true. Any use of a disabled extension or its referenced objects generates an INVALID_OPERATION error.

There are no other mechanisms to disable an extension.

Multiple calls to getExtension with the same extension string, taking into account case-insensitive comparison, must return the same object as long as the extension is enabled. An attempt to use any features of an extension without first calling getExtension to enable it must generate an appropriate GL error and must not make use of the feature.

This specification does not define any extensions. A separate WebGL extension registry defines extensions that may be supported by a particular WebGL implementation.

sequence<DOMString>? getSupportedExtensions() Returns a list of all the supported extension strings. object? getExtension(DOMString name) Returns an object if, and only if, name is an ASCII case-insensitive match [HTML] for one of the names returned from getSupportedExtensions ; otherwise, returns null . The object returned from getExtension contains any constants or functions provided by the extension. A returned object may have no constants or functions if the extension does not define any, but a unique object must still be returned. That object is used to indicate that the extension has been enabled.

WebGL generates a WebGLContextEvent event in response to a status change to the WebGL rendering context associated with the HTMLCanvasElement which has a listener for this event. Events are sent using the DOM Event System [DOM3EVENTS]. Event types can include the loss or restoration of state, or the inability to create a context. EventInit is defined in the DOM4 specification [DOM4].

WebGLContextEvent

type

cancelable

isTrusted

[Constructor(DOMString type, optional WebGLContextEventInit eventInit)] interface WebGLContextEvent : Event { readonly attribute DOMString statusMessage; }; // EventInit is defined in the DOM4 specification. dictionary WebGLContextEventInit : EventInit { DOMString statusMessage; };

The task source for all tasks queued [HTML] in this section is the WebGL task source.

Attributes

The following attributes are available:

statusMessage of type DOMString A string containing additional information, or the empty string if no additional information is available.

When the user agent detects that the drawing buffer associated with a WebGLRenderingContext context has been lost, it must run the following steps:

webglcontextlost event and enables the webglcontextrestored event to be delivered: canvas.addEventListener("webglcontextlost", function(e) { e.preventDefault(); }, false); The following code prevents the default behavior of theevent and enables theevent to be delivered:

The Context Restored Event

When the user agent is to restore the drawing buffer for a WebGLRenderingContext context, it must run the following steps:

Once the context is restored, WebGL resources such as textures and buffers that were created before the context was lost are no longer valid. The application needs to reinitialize the context's state and recreate all such resources.

function initializeGame() { initializeWorld(); initializeResources(); } function initializeResources() { initializeShaders(); initializeBuffers(); initializeTextures(); // ready to draw, start the main loop renderFrame(); } function renderFrame() { updateWorld(); drawSkyBox(); drawWalls(); drawMonsters(); requestId = window.requestAnimationFrame( renderFrame, canvas); } canvas.addEventListener( "webglcontextlost", function (event) { // inform WebGL that we handle context restoration event.preventDefault(); // Stop rendering window.cancelAnimationFrame(requestId); }, false); canvas.addEventListener( "webglcontextrestored", function (event) { initializeResources(); }, false); initializeGame(); The following code illustrates how an application can handle context loss and restoration:

The Context Creation Error Event

When the user agent is to fire a WebGL context creation error at a canvas, it must perform the following steps:

Fire a WebGL context event named "webglcontextcreationerror" at canvas, optionally with its statusMessage attribute set to a platform dependent string about the nature of the failure.

var errorInfo = ""; function onContextCreationError(event) { canvas.removeEventListener( "webglcontextcreationerror", onContextCreationError, false); errorInfo = e.statusMessage || "Unknown"; } canvas.addEventListener( "webglcontextcreationerror", onContextCreationError, false); var gl = canvas.getContext("experimental-webgl"); if(!gl) { alert("A WebGL context could not be created.

Reason: " + errorInfo); } The following code illustrates how an application can retrieve information about context creation failure:

This section describes changes made to the WebGL API relative to the OpenGL ES 2.0 API to improve portability across various operating systems and devices.

In the WebGL API, a given buffer object may only be bound to one of the ARRAY_BUFFER or ELEMENT_ARRAY_BUFFER binding points in its lifetime. This restriction implies that a given buffer object may contain either vertices or indices, but not both.

The type of a WebGLBuffer is initialized the first time it is passed as an argument to bindBuffer . A subsequent call to bindBuffer which attempts to bind the same WebGLBuffer to the other binding point will generate an INVALID_OPERATION error, and the state of the binding point will remain untouched.

No Client Side Arrays

The WebGL API does not support client-side arrays. If vertexAttribPointer is called without a WebGLBuffer bound to the ARRAY_BUFFER binding point, an INVALID_OPERATION error is generated. If drawElements is called with a count greater than zero, and no WebGLBuffer is bound to the ELEMENT_ARRAY_BUFFER binding point, an INVALID_OPERATION error is generated.

No Default Textures

The WebGL API does not support default textures. A non-null WebGLTexture object must be bound in order for texture-related operations and queries to succeed.

The offset arguments to drawElements and vertexAttribPointer , and the stride argument to vertexAttribPointer , must be a multiple of the size of the data type passed to the call, or an INVALID_OPERATION error is generated.

If a vertex attribute is enabled as an array via enableVertexAttribArray but no buffer is bound to that attribute via bindBuffer and vertexAttribPointer , then calls to drawArrays or drawElements will generate an INVALID_OPERATION error.

If a vertex attribute is enabled as an array, a buffer is bound to that attribute, and the attribute is consumed by the current program, then calls to drawArrays and drawElements will verify that each referenced vertex lies within the storage of the bound buffer. If the range specified in drawArrays or any referenced index in drawElements lies outside the storage of the bound buffer, an INVALID_OPERATION error is generated and no geometry is drawn.

If a vertex attribute is enabled as an array, a buffer is bound to that attribute, but the attribute is not consumed by the current program, then regardless of the size of the bound buffer, it will not cause any error to be generated during a call to drawArrays or drawElements .

WebGL adds the DEPTH_STENCIL_ATTACHMENT framebuffer object attachment point and the DEPTH_STENCIL renderbuffer internal format. To attach both depth and stencil buffers to a framebuffer object, call renderbufferStorage with the DEPTH_STENCIL internal format, and then call framebufferRenderbuffer with the DEPTH_STENCIL_ATTACHMENT attachment point.

A renderbuffer attached to the DEPTH_ATTACHMENT attachment point must be allocated with the DEPTH_COMPONENT16 internal format. A renderbuffer attached to the STENCIL_ATTACHMENT attachment point must be allocated with the STENCIL_INDEX8 internal format. A renderbuffer attached to the DEPTH_STENCIL_ATTACHMENT attachment point must be allocated with the DEPTH_STENCIL internal format.

In the WebGL API, it is an error to concurrently attach renderbuffers to the following combinations of attachment points:

DEPTH_ATTACHMENT + DEPTH_STENCIL_ATTACHMENT

STENCIL_ATTACHMENT + DEPTH_STENCIL_ATTACHMENT

DEPTH_ATTACHMENT + STENCIL_ATTACHMENT

checkFramebufferStatus must return FRAMEBUFFER_UNSUPPORTED .

must return . The following calls, which either modify or read the framebuffer, must generate an INVALID_FRAMEBUFFER_OPERATION error and return early, leaving the contents of the framebuffer, destination texture or destination memory untouched. clear copyTexImage2D copyTexSubImage2D drawArrays drawElements readPixels

error and return early, leaving the contents of the framebuffer, destination texture or destination memory untouched.

COLOR_ATTACHMENT0 = RGBA/UNSIGNED_BYTE texture

= texture COLOR_ATTACHMENT0 = RGBA/UNSIGNED_BYTE texture + DEPTH_ATTACHMENT = DEPTH_COMPONENT16 renderbuffer

= texture + = renderbuffer COLOR_ATTACHMENT0 = RGBA/UNSIGNED_BYTE texture + DEPTH_STENCIL_ATTACHMENT = DEPTH_STENCIL renderbuffer

Unless width and height parameters are explicitly specified, the width and height of the texture set by texImage2D and the width and height of the sub-rectangle updated by texSubImage2D are determined based on the uploaded TexImageSource source object:

source of type ImageData The width and height of the texture are set to the current values of the width and height properties of the ImageData object, representing the actual pixel width and height of the ImageData object. source of type HTMLImageElement If a bitmap is uploaded, the width and height of the texture are set to the width and height of the uploaded bitmap in pixels. If an SVG image is uploaded, the width and height of the texture are set to the current values of the width and height properties of the HTMLImageElement object. source of type HTMLCanvasElement The width and height of the texture are set to the current values of the width and height properties of the HTMLCanvasElement object. source of type HTMLVideoElement The width and height of the texture are set to the width and height of the uploaded frame of the video in pixels.

The WebGL API supports the following additional parameters to pixelStorei .

UNPACK_FLIP_Y_WEBGL of type boolean If set, then during any subsequent calls to texImage2D or texSubImage2D , the source data is flipped along the vertical axis, so that conceptually the last row is the first one transferred. The initial value is false . Any non-zero value is interpreted as true . UNPACK_PREMULTIPLY_ALPHA_WEBGL of type boolean If set, then during any subsequent calls to texImage2D or texSubImage2D , the alpha channel of the source data, if present, is multiplied into the color channels during the data transfer. The initial value is false . Any non-zero value is interpreted as true . UNPACK_COLORSPACE_CONVERSION_WEBGL of type unsigned long If set to BROWSER_DEFAULT_WEBGL , then the browser's default colorspace conversion is applied during subsequent texImage2D and texSubImage2D calls taking HTMLImageElement . The precise conversions may be specific to both the browser and file type. If set to NONE , no colorspace conversion is applied. The initial value is BROWSER_DEFAULT_WEBGL .

In the WebGL API, functions which read the framebuffer ( copyTexImage2D , copyTexSubImage2D , and readPixels ) are defined to generate the RGBA value (0, 0, 0, 0) for any pixel which is outside of the bound framebuffer.

In the WebGL API it is illegal to specify a different mask or reference value for front facing and back facing triangles in stencil operations. A call to drawArrays or drawElements will generate an INVALID_OPERATION error if:

STENCIL_WRITEMASK != STENCIL_BACK_WRITEMASK (as specified by stencilMaskSeparate for the mask parameter associated with the FRONT and BACK values of face , respectively)

!= (as specified by for the parameter associated with the FRONT and BACK values of , respectively) STENCIL_VALUE_MASK != STENCIL_BACK_VALUE_MASK (as specified by stencilFuncSeparate for the mask parameter associated with the FRONT and BACK values of face , respectively)

!= (as specified by for the parameter associated with the FRONT and BACK values of , respectively) STENCIL_REF != STENCIL_BACK_REF (as specified by stencilFuncSeparate for the ref parameter associated with the FRONT and BACK values of face , respectively)

The WebGL API supports vertex attribute data strides up to 255 bytes. A call to vertexAttribPointer will generate an INVALID_VALUE error if the value for the stride parameter exceeds 255.

The WebGL API does not support depth ranges with where the near plane is mapped to a value greater than that of the far plane. A call to depthRange will generate an INVALID_OPERATION error if zNear is greater than zFar .

In the WebGL API, constant color and constant alpha cannot be used together as source and destination factors in the blend function. A call to blendFunc will generate an INVALID_OPERATION error if one of the two factors is set to CONSTANT_COLOR or ONE_MINUS_CONSTANT_COLOR and the other to CONSTANT_ALPHA or ONE_MINUS_CONSTANT_ALPHA . A call to blendFuncSeparate will generate an INVALID_OPERATION error if srcRGB is set to CONSTANT_COLOR or ONE_MINUS_CONSTANT_COLOR and dstRGB is set to CONSTANT_ALPHA or ONE_MINUS_CONSTANT_ALPHA or vice versa.

Fixed point support

GL_FIXED

Per Supported GLSL Constructs, identifiers starting with "webgl_" and "_webgl_" are reserved for use by WebGL.

In the OpenGL ES 2.0 API, the available extensions are determined by calling glGetString(GL_EXTENSIONS) , which returns a space-separated list of extension strings. In the WebGL API, the EXTENSIONS enumerant has been removed. Instead, getSupportedExtensions must be called to determine the set of available extensions.

The core WebGL specification does not define any supported compressed texture formats. Therefore, in the absence of any other extensions being enabled:

The compressedTexImage2D and compressedTexSubImage2D methods generate an INVALID_ENUM error.

and methods generate an error. Calling getParameter with the argument COMPRESSED_TEXTURE_FORMATS returns a zero-length array (of type Uint32Array ).

The GLSL ES spec [GLES20GLSL] does not define a limit to the length of tokens. WebGL requires support of tokens up to 256 characters in length. Shaders containing tokens longer than 256 characters must fail to compile.

The GLSL ES spec [GLES20GLSL] defines the source character set for the OpenGL ES shading language to be ISO/IEC 646:1991, commonly called ASCII [ASCII]. If a string containing a character not in this set is passed to any of the shader-related entry points bindAttribLocation , getAttribLocation , getUniformLocation , or shaderSource , an INVALID_VALUE error will be generated. The exception is that any character allowed in an HTML DOMString [DOMSTRING] may be used in GLSL comments. Such use must not generate an error.

Some GLSL implementations disallow characters outside the ASCII range, even in comments. The WebGL implementation needs to prevent errors in such cases. The recommended technique is to preprocess the GLSL string, removing all comments, but maintaining the line numbering for debugging purposes by inserting newline characters as needed.

WebGL imposes a limit on the nesting of structures in GLSL shaders. Nesting occurs when a field in a struct refers to another struct type; the GLSL ES spec [GLES20GLSL] forbids embedded structure definitions. The fields in a top-level struct definition have a nesting level of 1.

WebGL requires support of a structure nesting level of 4. Shaders containing structures nested more than 4 levels deep must fail to compile.

WebGL imposes a limit of 256 characters on the lengths of uniform and attribute locations.

In the WebGL API, the enumerants INFO_LOG_LENGTH , SHADER_SOURCE_LENGTH , ACTIVE_UNIFORM_MAX_LENGTH , and ACTIVE_ATTRIBUTE_MAX_LENGTH have been removed. In the OpenGL ES 2.0 API, these enumerants are needed to determine the size of buffers passed to calls like glGetActiveAttrib . In the WebGL API, the analogous calls ( getActiveAttrib , getActiveUniform , getProgramInfoLog , getShaderInfoLog , and getShaderSource ) all return DOMString .

Texture Type in TexSubImage2D Calls

In the WebGL API, the type argument passed to texSubImage2D must match the type used to originally define the texture object (i.e., using texImage2D ).

The OpenGL ES Shading Language, Version 1.00 [GLES20GLSL], Appendix A, Section 7 "Counting of Varyings and Uniforms" defines a conservative algorithm for computing the storage required for all of the uniform and varying variables in a shader. The GLSL ES specification requires that if the packing algorithm defined in Appendix A succeeds, then the shader must succeed compilation on the target platform. The WebGL API further requires that if the packing algorithm fails either for the uniform variables of a shader or for the varying variables of a program, compilation or linking must fail.

Instead of using a fixed size grid of registers, the number of rows in the target architecture is determined in the following ways:

when counting uniform variables in a vertex shader: getParameter(MAX_VERTEX_UNIFORM_VECTORS)

when counting uniform variables in a fragment shader: getParameter(MAX_FRAGMENT_UNIFORM_VECTORS)

when counting varying variables: getParameter(MAX_VARYING_VECTORS)

Feedback Loops Between Textures and the Framebuffer

In the OpenGL ES 2.0 API, it's possible to make calls that both write to and read from the same texture, creating a feedback loop. It specifies that where these feedback loops exist, undefined behavior results.

In the WebGL API, such operations that would cause such feedback loops (by the definitions in the OpenGL ES 2.0 spec) will instead generate an INVALID_OPERATION error.

In the OpenGL ES 2.0 API, it is not specified what happens when a command tries to source data from a missing attachment, such as ReadPixels of color data from a complete framebuffer that does not have a color attachment.

In the WebGL API, such operations that require data from an attachment that is missing will generate an INVALID_OPERATION error. This applies to the following functions:

copyTexImage2D

copyTexSubImage2D

readPixels

In the WebGL API, if the width parameter passed to lineWidth is set to NaN, an INVALID_VALUE error is generated and the line width is not changed.

It is possible for an application to bind more than one attribute name to the same location. This is referred to as aliasing. When more than one attributes that are aliased to the same location are active in the executable program, linkProgram should fail.

References

Normative references

Other references

Acknowledgments

This specification is produced by the Khronos WebGL Working Group.

Special thanks to: Arun Ranganathan (Mozilla), Chris Marrin (Apple), Jon Leech, Kenneth Russell (Google), Kenneth Waters (Google), Mark Callow (HI), Mark Steele (Mozilla), Oliver Hunt (Apple), Tim Johansson (Opera), Vangelis Kokkevis (Google), Vladimir Vukicevic (Mozilla), Gregg Tavares (Google)

Additional thanks to: Alan Hudson (Yumetech), Benoit Jacob (Mozilla), Bill Licea Kane (AMD), Boris Zbarsky (Mozilla), Cameron McCormack (Mozilla), Cedric Vivier (Zegami), Dan Gessel (Apple), David Ligon (Qualcomm), David Sheets (Ashima Arts), Glenn Maynard, Greg Roth (Nvidia), Jacob Strom (Ericsson), Jeff Gilbert (Mozilla), Kari Pulli (Nokia), Teddie Stenvi (ST-Ericsson), Neil Trevett (Nvidia), Per Wennersten (Ericsson), Per-Erik Brodin (Ericsson), Shiki Okasaka (Google), Tom Olson (ARM), Zhengrong Yao (Ericsson), and the members of the Khronos WebGL Working Group.