lunedì 15 settembre 2014

What's coming to Green Island: part 1


I want to share with you some of the progress I recently made.
This is not all, more will come in another post.

Multi output support: part 1

Green Island now supports multiple outputs.

QtCompositor only support one output so in order to do this I did a little abstraction to enumarate outputs and played with QML to show them in the compositor window.

How does it work?

It's pretty simple: it has a ScreenModel that provides data such as name, primary boolean flag and geometry. The main QML file has a repeater using this model to create an OutputView for each output.

Every OutputView has layers to stack different kind of windows (panels, lock screen, workspaces), one of the layers is HotCorners which contains 8 hot corners.

During test and development one often need to fake outputs to test several different configurations without having real monitors, but this requires a dedicated backend and a configuration format.

So ScreenModel has its own backend code, one of the backends is based on QScreen and the other is for fake outputs.

Studying the problem and doing some prototype made me realize that QScreen has a very limited API (for example it doesn't detect when the primary output changes) and that this matter was already implemented with libkscreen.

It happens to be a framework that doesn't pull in undesired dependencies, so now Green Island is using it and I have to say it saved me a lot of work.

In the video below you can see a Green Island window with two 1024x768 outputs side by side, at some point the first one (which is also primary) is removed and all the windows are migrated to the other output that is now the new primary output.


Multi output support: part 2

A single big fat window for all the outputs is not such a great idea, it was good enough to continue the development keeping multiple outputs in mind but it's not the solution in the long run.

Such a solution may hit hardware limits pretty, plus outputs can have a different refresh rate so they really should not be done this way.

QtCompositor handles only one window so I patched it to be aware of multiple outputs with one window for each of them.
The patch targets the dev branch and at the time of this writing is in the review queue.

All the QML code was reused except for the Repeater and the logic to move windows when an output goes away was moved to C++.
This means that almost none of the code previously wrote was removed.

The hard part came when I needed to figure out how to show the same surface on multiple output windows.

Considering that QQuickItems cannot be shared between multiple windows I had to create a view for each output.

When a shell surface is created for a surface, the compositor creates a view that inherits from QQuickItem, the output is assigned based on the mouse pointer coordinates. No other view is created at this time because the position is calculated to be within output bounds considering the surface size.

More views are created on demand when the surface is mapped.

As windows are moved all views are moved accordingly, global coordinates are mapped to the output coordinates so that windows are shown only where they are meant to be.

Unresponsive applications

Wayland offers a ping/pong API that compositors use to know whether a surface is responsive or not, even with CSD (in the past there was some concern about this).

When a window is clicked, Green Island ping the surface and if it doesn't reply with a pong within 200ms it marks it as unresponsive and apply a colorize effect, draw some explanatory text, and intercepts mouse input. It also adds a couple of push buttons, one to wait for the application to become available again and the other to brutally murder the application.



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