[Pixman] Issue observed with Pixman 0.28.0 series

[vikram fugro]

Hi all,

I have observed few issues with the rendercheck utility (from X) with the
"triangles" use case
for operators src, clear, In , out.

Using a simple usecase: (with "Src" render operator)
./rendercheck -f r8g8b8 (or a8r8g8b8) -t triangles -o Src
--minimalrendering.

I am not an expert here, but what I know is, that this test case basically
composites 2 triangles (red in color)
on a white background and then reads back the value for crosschecking. The
test gets the desired red values
inside the triangles but outside the triangles it gets  black (should be
white, as the background window is white).

Debugging into the pixman library, I noticed the
pixman_composite_trapezoids().
In that, the get_trap_extents() (newly added) is setting the box region
(x1, x2, y1, y2) to the whole "dest" width & height,
as opposed to setting only the region of interest (trapezoids). This is
mainly because of the  zero_src_has_no_effect[] array,
making the function to set these values.
This causes the the background to go black with a red block (trapezoids) on
top. (as observed on display)

Is this a bug with the way rendercheck (or X)  is using the new pixman or
the bug is in pixman itself?
This issue was not observed with the previous versions.

I am not at all sure here. Help appreciated!

Thanks.
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