With KWin GLES shortly before the merge into workspace master (after git transition), it’s time to look back what I promised to deliver half a year ago, when I first talked about the idea of porting KWin to OpenGL ES at Akademy.
At the time of Akademy I had not yet started to write any code as I considered 4.5 more important and waited for the git transition. Obviously I stopped waiting for git or there would not be any code written 😉 My schedule presented at Akademy looked like that:
- Remove deprecated OpenGL code
- Remove unused code in Scene and Eﬀects Lib
- Drop XGL support
- Port to OpenGL ES 1.1 till 4.6
- Port to OpenGL 3 and ES 2.0 till 4.7
Removal of deprecated OpenGL code is mostly done. With GLES KWin has a forward compatible code path, though we still have OpenGL 1.x code for legacy systems and that won’t be dropped in the near future. Considering deprecated OpenGL 1.x code it’s looking quite good, e.g. glBegin/glEnd is removed in the GLES branch. Rendering of geometries is abstracted and the backend performs a runtime check whether legacy or modern rendering is invoked.
For 4.6 I started to port some effects to newer functionality which allowed to drop some then unused code. The remaining functions have been marked as deprecated, but are not yet removed in the GLES branch as they are still used by the Shadow effect (though unavailable in OpenGL ES and broken with OpenGL 2 backend). Given that Shadow is difficult to port, in general broken and unmaintained I consider to just drop it. I am already gathering ideas for a new replacement effect.
The XGL code (XGL was needed to run Compiz before AIGLX was integrated) is still in KWin and should really be dropped. It has been removed from X git tree for quite some time and I doubt anybody has ever run KWin with XGL. There are more things we can now consider to remove: shared memory and "fallback" compositing. Together this will mean a requirement to Texture from Pixmap. That’s pretty well supported nowadays on all drivers and anything else cannot be recommended.
The next bullet point is OpenGL ES 1.1. Well I noticed that it would really clutter the code, so I stopped working on it and switched to going to ES 2.0 directly. My initial plan was to provide 1.1 support at the time of the 4.6 release. Instead we now have ES 2.0 support at the time of 4.6 😀
In 4.7 we will not only have an OpenGL ES 2.0 backend available, it will be integrated into the release. As a side effect it gives us a complete OpenGL 2.x backend which should benefit all users having decent drivers. I’ll soon integrate an option to the advanced settings tab to choose between OpenGL 1.x, 2.x and 3.x. With the 2.x code there, it’s really easy to go to 3.x. We won’t default to it, we will hardly use it (I want to experiment with Geometry Shaders in MagicLamp effect), but I hope that the drivers supporting OpenGL 3 (that’s for us only the NVIDIA blob at the moment, fglrx is only usable with OpenGL 1.x in the composited case) are more efficient if run in a forward compatible profile.
There is still lots to do and I want to concentrate on improving the rendering stack throughout the 4.7 release cycle. It’s quite fortunate that the new rendering stack can be integrated directly after the git transition. So I hope that lots of developers will be using it and can provide feedback for various hardware.
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