Texture Atlas Generator

One of the performance bottlenecks when rendering polygons using a dedicated GPU is the number of draw calls issued by the application. For textured polygons, you usually bind one texture for each draw call and all the polygons will be textured using this one texture. This means that you will get at least one draw call for every texture used in your application.

To reduce the number of draw calls for textured polygons, you can put all your individual textures files into one or more big texture files, also known as a texture atlas. This way all the polygons that use the same atlas can be batched together and rendered in one draw call.

If you have all your textures as separate files, then creating the atlas by hand can be a quite painstaking experience. I have therefor made this small, single file, Java application that will recursively load PNG (can easily be modified to support other formats) from a folder and create one or more PNG texture atlases.

Get it on GitHub : Texture Atlas Generator

The texture packing algorithm used in this atlas generator is the Lightmap Packing Algorithm by Black Pawn. The images are added to the atlas by area size (width x height), in descending order.

I will show how to use the atlas generator by example.

First I downloaded the abuse_png.zip archive from OpenGameArt.org and extracted the contents into a folder named “abuse_png” next AtlasGenerator.java.

I then compiled the application

javac AtlasGenerator.java

and executed it

java AtlasGenerator atlas-2048- 2048 2048 abuse_png/

This generated the atlas PNG texture below. Click the image below to get the full size image.

Along with the atlas image there is also a .txt file generated with coordinates for all the textures within the atlas.

The format for each entry is:

imagePath x y width height

Here is what the .txt file for the atlas above looks like.

abuse_png/ammo 400 765 108 69 abuse_png/ant 0 0 780 495 abuse_png/back_cave 836 867 300 120 abuse_png/back_city 1308 495 420 150 abuse_png/back_intro 1674 344 360 150 abuse_png/back_tech 1359 675 360 150 abuse_png/blowups 1136 867 301 96 abuse_png/bold 1505 351 153 86 abuse_png/cloud 1505 437 68 45 abuse_png/concus 1573 437 63 34 abuse_png/cop 780 0 429 462 abuse_png/coptop 1209 0 465 351 abuse_png/door 1926 195 72 120 abuse_png/door_round 330 1386 180 82 abuse_png/exp1 1719 675 280 192 abuse_png/flyer 0 1710 296 234 abuse_png/fonts 0 1556 512 154 abuse_png/fore_cave 918 495 390 165 abuse_png/fore_techno 1728 495 300 135 abuse_png/fore_techno2 540 1084 270 120 abuse_png/fore_techno3 330 1296 210 90 abuse_png/fore_techno4 0 1080 420 216 abuse_png/gun2 540 867 296 217 abuse_png/jug 540 495 378 180 abuse_png/lava 330 1468 190 36 abuse_png/lavap 296 1710 235 132 abuse_png/lightin 1926 0 114 195 abuse_png/mine 400 834 112 60 abuse_png/misc 0 765 400 315 abuse_png/missle 540 675 351 192 abuse_png/platform 891 675 468 134 abuse_png/push 780 462 252 22 abuse_png/rob1 1209 351 296 141 abuse_png/rob2 0 1296 330 260 abuse_png/sect 0 495 540 270 abuse_png/tdoor 0 1944 245 45 abuse_png/teleport 1674 0 252 344

If the images do not fit into one atlas of the specified size, then multiple atlases will be generated. The images below show the 3 atlases generated for the PNGs when setting

the size of the atlas to 1024×1024.

Below are 3 .txt files for the 3 images above.

abuse_png/ammo 894 252 108 69 abuse_png/ant 0 0 780 495 abuse_png/cloud 357 957 68 45 abuse_png/concus 780 453 63 34 abuse_png/cop 0 495 429 462 abuse_png/coptop 429 495 465 351 abuse_png/door 894 132 72 120 abuse_png/fonts 429 846 512 154 abuse_png/fore_techno3 780 327 210 90 abuse_png/lava 780 417 190 36 abuse_png/lavap 780 0 235 132 abuse_png/lightin 780 132 114 195 abuse_png/mine 245 957 112 60 abuse_png/push 429 1000 252 22 abuse_png/tdoor 0 957 245 45





abuse_png/back_cave 696 806 300 120 abuse_png/blowups 696 926 301 96 abuse_png/door_round 0 929 180 82 abuse_png/exp1 730 270 280 192 abuse_png/flyer 400 530 296 234 abuse_png/fore_techno 696 671 300 135 abuse_png/fore_techno4 540 0 420 216 abuse_png/gun2 400 764 296 217 abuse_png/misc 0 270 400 315 abuse_png/rob1 696 530 296 141 abuse_png/rob2 400 270 330 260 abuse_png/sect 0 0 540 270 abuse_png/teleport 0 585 252 344





abuse_png/back_city 351 180 420 150 abuse_png/back_intro 351 464 360 150 abuse_png/back_tech 351 614 360 150 abuse_png/bold 768 0 153 86 abuse_png/fore_cave 378 0 390 165 abuse_png/fore_techno2 0 372 270 120 abuse_png/jug 0 0 378 180 abuse_png/missle 0 180 351 192 abuse_png/platform 351 330 468 134