When kLightsMode (aka kInterpRGB) is false, "a" is always 0 (vertice data is
not used in caller in corresponding branches), so taking it into account makes
all triangles transparent.
This is not visible in practice, because putPixelTextureMappingPerspective is
only called when (kInterpST || kInterpSTZ) is true, and kInterpRGB is always
true when that's the case. But unifying color processing allows further code
simplification.
This reverts commit b8bddf64da.
Since 9b7548ccf7, alpha test is enabled
when drawing model faces, fixing transparency issues in GRIM which were
corrected by reverted commit.
It is incorrect to test transparency when caller did not enable it.
Also, this change bypasses increments done at the end of
putPixelTextureMappingPerspective, so transparent textures in 16 bits mode
would be stuck on the transparent pixel for the current line's 8-pixel run
in filTriangle, and would ignore z coordinate.
Increment y inside the loop, not outside.
Set y to the topmost vertex y coordinate, which depends on which half of
the triangle is being drawn.
Should have been part of:
commit 3c2689a65f
TINYGL: Optimise scissorPixel.
This does not (should not) fix any visible regression, as pixel scissor is
only (?) used when dirty rectangle mecanism is enabled (and it is disabled).
Scissor operations happen in a 2d rectangle, but it used to take a buffer
offset as a parameter. As a result, it had to divide that value with its
width, which is an expensive operation, which has to be done for each
pixel candidate for display (even before z-buffer comparison when
applicable, in current implementatoin).
But callers actually generate the buffer offset from rectangular
coordinates, so propagate these instead.
This sadly increases API redundancy, but saves a lot of time in a very
frequent occurrence (especially when enabling dirty rect mechanism,
which is not yet enabled by default).
Because writePixel may decide to not write anything (alpha test), in which
case no z-buffer write should happen.
Factorises code.
Fixes apparent back-face culling in GRIM behind transparent textures, like
the tube (the 3d-shape Manny takes out, not the flat image in foreground)
in set mo.
