Re: [glean-dev] blendFunc test

[Brian P. <br...@va...>]

Gareth Hughes wrote:
> 
> Here's a good one.  I'm running the blendFunc test with the Radeon
> driver, it's passing just fine at 16bpp, and failing at 32bpp.  All of
> the errors are on the alpha channel, but the pixels being read back
> contain the expected values.  I'm suspecting the problem lies somewhere
> after the driver reads the pixels from the framebuffer in the span
> functions, and before glean gets the pixel values back.
> 
> Here's the (0,0) pixel data being read back, obviously containing alpha
> values (in ARGB8888 format):
> 
>    x=1 y=1 p=0x6fb39c21
>    x=1 y=1 p=0x00000000
>    x=1 y=1 p=0x6fb39c21
>    x=1 y=1 p=0x6fb39c21
>    x=1 y=1 p=0x6fb39c21
>    x=1 y=1 p=0x18974e06
>    x=1 y=1 p=0x6fb39c21
>    x=1 y=1 p=0x561b4e1a
>    x=1 y=1 p=0x6fb39c21
>    x=1 y=1 p=0x18272207
>    x=1 y=1 p=0x6fb39c21
>    x=1 y=1 p=0x568b7919
>    x=1 y=1 p=0x6fb39c21
>    x=1 y=1 p=0x304e440e
> 
> And here's the test failure message:
> 
> blendFunc:  FAIL rgba8, db, z24, win+pmap, id 0
>         source factor = GL_ZERO, dest factor = GL_ZERO
>         Readback had 8 bits in error; blending had 0 bits in error.
> 
> First failing pixel is at row 0 column 0
> Actual values are (0.698039, 0.678431, 0.678431, 0)
> Expected values are (0.698039, 0.678431, 0.678431, 0.239216)
> Errors are (0, 0, 0, 0.239216)
> Source values are (0.176471, 0.886275, 0.988235, 0.252338)
> Destination values are (0.698039, 0.678431, 0.678431, 0.239216)
> 
> Any ideas?  This doesn't appear to be a driver error, and I haven't seen
> anything like this before.

Check the call to Mesa's gl_create_framebuffer() function and make sure
you're not telling Mesa to maintain a software alpha channel.

That could cause trouble.

-Brian