[haiku-appserver] Quite some room for improvement

Hi all,

The good news is that I've found a way to accelerate the alpha blending 
inside the drawing modes that Painter uses by a factor of 4.6. For writing 
to graphics memory, the access pattern doesn't seem to matter much. There 
is virtually no difference if you write 8 bits, 32 bits or 64 bits at once. 
But when you need to read from the frame buffer, the difference is quite 
noticable: It is 3.6 times faster to read 32 bits into a temporary 
variable, alpha blend into that, and write it back. 4.6 times faster to do 
them same, but with 64 bits. I always thought that this stuff mattered for 
just writing to graphics mem as well, but it seems that this is not the 
case.

I've also noticed an awesome possibility for speed improvement in my bitmap 
rendring code for clipped bitmaps. This should speed up WonderBrush on 
Haiku quite a bit. Maybe this applies to more stuff as well. If I 
understand AGG correctly, it will clip stuff you draw at a very late stage, 
mostly at the time it tries to write a generated scanline to the frame 
buffer. When you manually apply a bit of clipping before that, you can 
possibly skip the generation of much of the scanline as well. For bitmaps, 
this is especially easy to accomplish. And even more effective, since AGG 
would generate a color scanline, since the "fill" is not a solid color.

Best regards,
-Stephan

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