Today the OGL pipeline only "accelerates" antialiased rendering (via the OGLMaskFill
primitive) in the following cases:
  - AlphaComposite.SrcOver
  - AlphaComposite.Src, extra alpha == 1.0, source paint is opaque

The reason we can't support any arbitrary AlphaComposite mode is because of the
way the MaskFill operation is defined:
    dst = ((src <MODE> dst) * maskA) + (dst * (1 - maskA))

This can be simplified as follows for the above modes, which can then be easily
accelerated via OpenGL using its built-in blending functions:
    dst = (src * maskA) <SrcOver> dst

Implementing most of the other AlphaComposite rules would require performing the
compositing step in a shader, which can be tricky given that the framebuffer contents
are not accessible from a fragment shader.  This bug report proposes to make changes
to OGLMaskFill and OGLPaints so that it becomes possible to accelerate these other
AlphaComposite modes when fragment shaders are available in hardware.  This
approach should be much faster than the software-based loops that we fall back on
today in these cases, because it won't be necessary to suffer the cost of reading
back from VRAM into system memory to perform the compositing operation.  In addition,
these changes will pave the way for accelerating the extended compositing modes
that are proposed in 5094232.
Posted Date : 2007-03-06 21:18:01.0

N/A

This will require a fair amount of changes to OGLMaskFill and related code,
but it should be well worth it from the performance standpoint.
Posted Date : 2007-03-06 21:28:25.0

Here are some preliminary results on an Nvidia Quadro FX 1100, Solaris 10:

Options common across all tests:
  testname=graphics.render.tests.shape.fillCubic
  graphics.opts.xormode=false
  graphics.opts.renderhint=Default
  graphics.opts.extraalpha=false
  graphics.render.opts.alphacolor=false
  global.dest=VolatileImg
  graphics.opts.sizes=250
  graphics.opts.clip=false
  graphics.opts.anim=2

graphics.opts.alpharule=SrcAtop,graphics.render.opts.antialias=false,graphics.render.opts.paint=gradient2:
1100.old: 300766.85695 (var=10.66%) (100.0%)
1100.new: 298545.28571 (var=0.75%) (99.26%)
graphics.opts.alpharule=SrcAtop,graphics.render.opts.antialias=false,graphics.render.opts.paint=radial3:
1100.old: 21654.07635 (var=0.03%) (100.0%)
1100.new: 21661.29919 (var=0.03%) (100.03%)
graphics.opts.alpharule=SrcAtop,graphics.render.opts.antialias=false,graphics.render.opts.paint=single:
1100.old: 372773.04715 (var=0.98%) (100.0%)
1100.new: 372629.36198 (var=0.47%) (99.96%)
graphics.opts.alpharule=SrcAtop,graphics.render.opts.antialias=true,graphics.render.opts.paint=gradient2:
1100.old: 697.0569663 (var=0.17%) (100.0%)
1100.new: 11774.60753 (var=0.4%) (1689.19%)
graphics.opts.alpharule=SrcAtop,graphics.render.opts.antialias=true,graphics.render.opts.paint=radial3:
1100.old: 600.9538461 (var=0.44%) (100.0%)
1100.new: 9941.513684 (var=0.5%) (1654.29%)
graphics.opts.alpharule=SrcAtop,graphics.render.opts.antialias=true,graphics.render.opts.paint=single:
1100.old: 701.3525991 (var=1.85%) (100.0%)
1100.new: 14568.63994 (var=0.55%) (2077.22%)
graphics.opts.alpharule=SrcOver,graphics.render.opts.antialias=false,graphics.render.opts.paint=gradient2:
1100.old: 299639.26258 (var=0.8%) (100.0%)
1100.new: 298351.90947 (var=0.67%) (99.57%)
graphics.opts.alpharule=SrcOver,graphics.render.opts.antialias=false,graphics.render.opts.paint=radial3:
1100.old: 21654.78452 (var=0.0%) (100.0%)
1100.new: 21654.78452 (var=3.17%) (100.0%)
graphics.opts.alpharule=SrcOver,graphics.render.opts.antialias=false,graphics.render.opts.paint=single:
1100.old: 371642.69090 (var=4.02%) (100.0%)
1100.new: 374840.04719 (var=3.6%) (100.86%)
graphics.opts.alpharule=SrcOver,graphics.render.opts.antialias=true,graphics.render.opts.paint=gradient2:
1100.old: 16357.54375 (var=0.14%) (100.0%)
1100.new: 16480.93529 (var=0.03%) (100.75%)
graphics.opts.alpharule=SrcOver,graphics.render.opts.antialias=true,graphics.render.opts.paint=radial3:
1100.old: 12316.90647 (var=0.14%) (100.0%)
1100.new: 12299.01802 (var=0.44%) (99.85%)
graphics.opts.alpharule=SrcOver,graphics.render.opts.antialias=true,graphics.render.opts.paint=single:
1100.old: 23127.22672 (var=0.97%) (100.0%)
1100.new: 23204.01414 (var=0.87%) (100.33%)

Summary:
  1100.old: 
    Number of tests:  12
    Overall average:  120160.97990377284
    Best spread:      0.0% variance
    Worst spread:     10.66% variance
    (Basis for results comparison)

  1100.new: 
    Number of tests:  12
    Overall average:  122995.95139373116
    Best spread:      0.03% variance
    Worst spread:     3.6% variance
    Comparison to basis:
      Best result:      2077.22% of basis
      Worst result:     99.26% of basis
      Number of wins:   3
      Number of ties:   9
      Number of losses: 0

As you can see, no change in performance for operations that were already
accelerated, and a 16x to 20x improvement for non-SrcOver antialiased
operations.  Comparing to the software loops (X11 pipeline enabled), it
appears that we still have some work to do for AA performance (but a
bug has recently been filed for that issue, see 6529101):

Options common across all tests:
  testname=graphics.render.tests.shape.fillCubic
  graphics.opts.xormode=false
  graphics.opts.renderhint=Default
  graphics.opts.extraalpha=false
  graphics.render.opts.alphacolor=false
  global.dest=VolatileImg
  graphics.opts.sizes=250
  graphics.opts.clip=false
  graphics.opts.anim=2

graphics.opts.alpharule=SrcAtop,graphics.render.opts.antialias=false,graphics.render.opts.paint=gradient2:
1100.x11: 7747.997644 (var=0.07%) (100.0%)
1100.old: 300766.85695 (var=10.66%) (3881.87%)
1100.new: 298545.28571 (var=0.75%) (3853.19%)
graphics.opts.alpharule=SrcAtop,graphics.render.opts.antialias=false,graphics.render.opts.paint=radial3:
1100.x11: 3929.818273 (var=0.34%) (100.0%)
1100.old: 21654.07635 (var=0.03%) (551.02%)
1100.new: 21661.29919 (var=0.03%) (551.2%)
graphics.opts.alpharule=SrcAtop,graphics.render.opts.antialias=false,graphics.render.opts.paint=single:
1100.x11: 8515.886255 (var=0.81%) (100.0%)
1100.old: 372773.04715 (var=0.98%) (4377.38%)
1100.new: 372629.36198 (var=0.47%) (4375.7%)
graphics.opts.alpharule=SrcAtop,graphics.render.opts.antialias=true,graphics.render.opts.paint=gradient2:
1100.x11: 15937.13917 (var=0.27%) (100.0%)
1100.old: 697.0569663 (var=0.17%) (4.37%)
1100.new: 11774.60753 (var=0.4%) (73.88%)
graphics.opts.alpharule=SrcAtop,graphics.render.opts.antialias=true,graphics.render.opts.paint=radial3:
1100.x11: 3548.736074 (var=0.07%) (100.0%)
1100.old: 600.9538461 (var=0.44%) (16.93%)
1100.new: 9941.513684 (var=0.5%) (280.14%)
graphics.opts.alpharule=SrcAtop,graphics.render.opts.antialias=true,graphics.render.opts.paint=single:
1100.x11: 22568.86582 (var=0.07%) (100.0%)
1100.old: 701.3525991 (var=1.85%) (3.11%)
1100.new: 14568.63994 (var=0.55%) (64.55%)
graphics.opts.alpharule=SrcOver,graphics.render.opts.antialias=false,graphics.render.opts.paint=gradient2:
1100.x11: 5737.476861 (var=2.68%) (100.0%)
1100.old: 299639.26258 (var=0.8%) (5222.49%)
1100.new: 298351.90947 (var=0.67%) (5200.05%)
graphics.opts.alpharule=SrcOver,graphics.render.opts.antialias=false,graphics.render.opts.paint=radial3:
1100.x11: 4271.989063 (var=29.16%) (100.0%)
1100.old: 21654.78452 (var=0.0%) (506.9%)
1100.new: 21654.78452 (var=3.17%) (506.9%)
graphics.opts.alpharule=SrcOver,graphics.render.opts.antialias=false,graphics.render.opts.paint=single:
1100.x11: 441439.77005 (var=2.15%) (100.0%)
1100.old: 371642.69090 (var=4.02%) (84.19%)
1100.new: 374840.04719 (var=3.6%) (84.91%)
graphics.opts.alpharule=SrcOver,graphics.render.opts.antialias=true,graphics.render.opts.paint=gradient2:
1100.x11: 17496.38276 (var=0.55%) (100.0%)
1100.old: 16357.54375 (var=0.14%) (93.49%)
1100.new: 16480.93529 (var=0.03%) (94.2%)
graphics.opts.alpharule=SrcOver,graphics.render.opts.antialias=true,graphics.render.opts.paint=radial3:
1100.x11: 3621.170480 (var=0.7%) (100.0%)
1100.old: 12316.90647 (var=0.14%) (340.14%)
1100.new: 12299.01802 (var=0.44%) (339.64%)
graphics.opts.alpharule=SrcOver,graphics.render.opts.antialias=true,graphics.render.opts.paint=single:
1100.x11: 26587.40460 (var=0.34%) (100.0%)
1100.old: 23127.22672 (var=0.97%) (86.99%)
1100.new: 23204.01414 (var=0.87%) (87.27%)

Summary:
  1100.x11: 
    Number of tests:  12
    Overall average:  46783.55308965824
    Best spread:      0.07% variance
    Worst spread:     29.16% variance
    (Basis for results comparison)

  1100.old: 
    Number of tests:  12
    Overall average:  120160.97990377284
    Best spread:      0.0% variance
    Worst spread:     10.66% variance
    Comparison to basis:
      Best result:      5222.49% of basis
      Worst result:     3.11% of basis
      Number of wins:   6
      Number of ties:   0
      Number of losses: 6

  1100.new: 
    Number of tests:  12
    Overall average:  122995.95139373116
    Best spread:      0.03% variance
    Worst spread:     3.6% variance
    Comparison to basis:
      Best result:      5200.05% of basis
      Worst result:     64.55% of basis
      Number of wins:   7
      Number of ties:   0
      Number of losses: 5
Posted Date : 2007-03-07 04:51:49.0