[RQt-devel] opengl2 paint engine in qt 4.6

[Michael Lawrence]

I realized this week that Qt 4.6 gained an entirely new OpenGL paint engine
designed around OpenGL ES 2.0. While requiring 2.0 means cleaner code, the
'ES' stands for Embedded Systems, i.e. mobile phones. Thus, everything is
shader-based, where paths are built up and rendered with shaders. This is
probably very efficient on mobile hardware, but it completely misses the
obvious hardware fast paths for our simple cases. Tests show that drawing
lines and polygons are about 30X slower.

Ironically, Qt, wrt our use case, is moving backwards, while cairo is moving
forward with its new GL backend. The two approaches are now pretty similar
in design and potentially comparable in performance. My bet is that Qt has
the edge now, but cairo is progressing quickly. One could imagine a cairo
backend for whatever abstraction we develop over qtpaint.

Anyway, for now we're using the old 1.x backend. Let's hope it remains
supported and that Nokia does not steer Qt toward a mobile-oriented
framework.

Michael
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