KWin May Drop Support For Catalyst, Vintage GPUs
The KWin compositing window manager for KDE may drop its older OpenGL renderer, which would remove support for vintage GPUs/drivers, but this would also include eliminating -- at least temporarily -- support for the AMD Catalyst graphics driver.
Martin Gräßlin has written a blog post this afternoon entitled The Costs of Supporting Legacy Hardware. In this blog post Martin talks about the cost of supporting older graphics cards / drivers with the KWin compositing window manager for KDE users. In particular, he shares the troubles he has in supporting the older OpenGL 1.x renderer back-end for KWin. The OpenGL 2.x back-end, which is shared with the OpenGL ES 2.0 support too, is completely different from the old GL1 renderer.
He ends up saying that he may likely drop the OpenGL 1.x renderer from KWin as it's a support burden. A majority of hardware supports OpenGL 2.0+ (basically anything in more than the past half-decade), the GL2 code-paths are superior, and it's really just not worth maintaining the GL1 back-end any longer. Martin also mentions the XRender back-end for Kwin as being a cost with it being considered a "legacy support system" for those without proper OpenGL support.
To sum it up: we have increased complexity, increased maintenance costs and lots of code just for OpenGL 1.x related hardware which we cannot really test. So a rather bad situation. Additionally it is nothing which we can continue to support in the future. Neither Wayland nor Qt 5 will make sense on such hardware (XRender based compositing might still make sense with Qt 5, but as the name says not with Wayland).
So aside from those running deathly-slow hardware, Catalyst driver users at least temporarily would get shafted by this move. However, this may leave AMD no choice but to improve their GL code-paths that are stressed by KWin. The only other portion of users potentially affected in size would be those with Intel i945-based netbooks, which don't have full GL2 driver support in Mesa. All other worthwhile hardware and drivers out there are capable of handling OpenGL 2.0+ with KWin.
Martin does also mention the possibility of using LLVMpipe with KWin, which is something he is going to explore as a means of software acceleration. LLVMpipe already works quite well with the GNOME Shell, even in virtual machines, thanks to Gallium3D and LLVM. "If I am satisfied with the performance, I will be tempted to remove the OpenGL 1.x based legacy code..."
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