A few weeks ago I contacted Thomas Pfeiffer with the idea to design a new user interface for Klipper in Plasma 5.1. Surprisingly he informed me that a discussion was already started in the KDE Forums. Which is awesome as that means there was already some ideas on how the user interface could look like. Last week the number of new bug reports for KWin get lower so I started to look into Klipper for 5.1.

The old Klipper

The user interface of Klipper is based on a context menu and this restricts the possible interaction patterns. The task of Klipper is to hold a history of clipboard items and allow the user to select an old clipboard item and make it the current clipboard content. For this a context menu is a good solution as it allows the user to just select an item, it gets synced to the clipboard and the menu closes.

But Klipper offers more than just the clipboard history. It can perform various actions on the clipboard content:

Edit the clipboard content

Show a QR-code for the clipboard content

Remove content from history

Invoke actions (e.g. open link in browser) on clipboard content

Due to the nature of the context menu as user interface these actions can only be performed on the current clipboard item. Technically there is no reason for this restriction, but the user interface requires it. This in turn makes the usage interaction cumbersome: to show the QR-code of a previous item one needs to open Klipper, select the item – Klipper closes, open Klipper again and select the action to show the QR-code.

Also a problem with the current Klipper is that it doesn’t integrate with the environment. It sits in the notification area, but opens a QWidget styled menu. This makes Klipper an odd item in the system tray behaving different to all other items.

How Klipper should work in Plasma

A clipboard history is of course an important part of a desktop shell and thus should be a first class citizen. The user interface needs to be integrate and this means the interface needs to be provided by a Plasmoid which needs to be added to the notification area. The interface would still show a list and this is best done by providing the data in the form of a QAbstractItemModel.

As there should only be one clipboard history manager, but at the same time perhaps several user interfaces for it (e.g. one panel per screen) the QAbstractItemModel holding the data needs to be provided by a DataEngine. So overall we need to separate the user interface (Plasmoid) from the data storage (DataEngine) and turn the existing Klipper in just being the data storage.

How Klipper works internally

Internally Klipper consists of a History with HistoryItems in a circular double-linked list with a marked first item in the circle. Whenever the History changes the context menu gets repopulated on next show. Whenever the first item in the History changes Klipper syncs this item into the clipboard. This means the complete logic of Klipper interacts only with the History class. Which makes it a nice and clean interface. In a simplified class diagram Klipper looks like the following:

For creating the DataEngine we need access to the History and all items in it and put it into a QAbstractItemModel. There are two possible solutions: connect the QAbstractItemModel to the existing History or use the QAbstractItemModel as the new storage for the History instead of the own double linked list. As the current use of the History is to just mark everything as dirty and then to re-populate connecting the model to the History doesn’t sound like a good suggestion. Instead I investigated in using the model as the storage end. The design is then modified to look like the following:

To achieve this transition I first created a unit test to ensure that my transition doesn’t break the existing code. Then I created the model from scratch as well covered with unit tests and in a third step I hooked it into the existing History. With this transition both the use cases of the existing code base and the new DataEngine can be satisfied.

DataEngine, Service and co

With the model in place it’s time to make it available to Plasma. The tool of choice is the DataEngine which allows to export a model and can provide a Service allowing us to interact with Klipper. Of course it would be possible to add invokables to the model, but that would kind of destroy the design as the model is only supposed to be the data store. A Service which then interacts with our existing Klipper API is way cleaner. The task of the Service is to start ServiceJobs which will in turn interact with Klipper. Overall this looks now like this:

The Plasmoid

The last and maybe most important part of the rework is the user interface in form of a new Plasmoid. But that’s also the part I’m least interested in (perfer to work on backend) and are hoping for help on it 🙂 Given that the current user interface can and should only be considered as a draft. But it’s fully functional and support text and image elements, a filter (note: klipper supported filtering for quite some time, just start typing) and all the actions. But now the actions are available on each item and not just the latest one. In the current state with a vertical panel it looks like this:

Be aware that this is material for Plasma 5.1 – it won’t be part of the upcoming release. Also I should point out that it’s still possible to run the stand-alone Klipper application and that no features are removed. All global shortcuts and actions are still supported.