[Piglit] pixelzoom: New test for glPixelZoom()/glDrawPixels() validation

[Daniel J Sebald]

Hello Piglit,

Attached is a proposed test for glPixelZoom() that has a number of 
individual tests.  The test came about because of some vertical line 
artifacts appearing in the legacy swrast_dri.so driver on my system and 
apparently a couple others' systems I inquired with.

The tests consist of a gradient test to suss any problems with large 
input images spanning GL_MAX_TEXTURE_SIZE, a stringent endpoint value 
test to see if the driver is agreeing with the OpenGL formula 
definitions, and an alternating color residue test of successively 
smaller boxes to see if the scaling is being done correctly.

All tests are open for debate--point being that working out the 
correctness of the tests should in the long run make all drivers for 
various platforms more consistent.

For a good summary of the tests, browse through the PNG files showing 
the output image for each test for legacy, patched legacy, Gallium and 
simple-mod Gallium drivers here:

https://bugs.freedesktop.org/show_bug.cgi?id=89586

Regards,

Dan Sebald
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