So, I was playing 'foobillard' today and noticed that the table was drawn differently on my 965gm laptop compared with the i830 laptop sitting next to it.
The difference is generated from a texture:
glGenTextures(1,&tabletexbind);
load_png("tabletex_fB_256x256.png",&tabletexw,&tabletexh,&depth,&tabletexdata);
glBindTexture(GL_TEXTURE_2D,tabletexbind);
gluBuild2DMipmaps(GL_TEXTURE_2D, 1, tabletexw, tabletexh, GL_LUMINANCE,
GL_UNSIGNED_BYTE, tabletexdata);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
options_tex_min_filter);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
options_tex_mag_filter);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
It seems unlikely to me that GL_CLAMP was really desired, I think that's
supposed to blend the edge pixel with the border color, and the program
doesn't bother to set a border color. Setting it to GL_CLAMP_TO_EDGE
'fixes' the problem, making the program look identical on 965gm and
i830.
Neither the i830 nor 965gm actually support GL_CLAMP natively (yay for
d3d-only hardware). The different appearance is caused by the 965 driver
mapping GL_CLAMP to GL_CLAMP_TO_BORDER while the i830 maps it to
GL_CLAMP_TO_EDGE. The 965 driver has a comment saying that glconform
prefers GL_CLAMP_TO_BORDER, while the i830 has a comment saying that the
Windows GL driver uses GL_CLAMP_TO_EDGE.
Several other drivers (savage, sis, unichrome) map GL_CLAMP to
GL_CLAMP_TO_EDGE.
What should I do now?
1) Fix the 965 driver to make GL_CLAMP work correctly (icky, and will
be slower).
2) Use GL_CLAMP_TO_EDGE in the 965 driver.
3) Use GL_CLAMP_TO_BORDER in the i830 driver.
4) Nothing.
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