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reftest-compare: Treat colour channels as undefined if alpha is zero

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If the alpha channel is zero, it doesn't matter what the values of the
red, green and blue channels are: the pixel is still fully transparent.
On most architectures, fully transparent pixels end up all-zeroes
(fully transparent black), matching what's in the reference PNG file;
but on mips*el the blend-difference and blend-normal tests get all-ones
(fully transparent white) and a test failure.

Resolves: https://gitlab.gnome.org/GNOME/gtk/-/issues/4227
Signed-off-by: Simon McVittie <smcv@debian.org>
This commit is contained in:
Simon McVittie 2021-09-02 22:34:14 +01:00
parent 82a184a7b7
commit 16b9a30655
1 changed files with 6 additions and 1 deletions
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7
testsuite/reftests/reftest-compare.c
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@ -104,7 +104,12 @@ buffer_diff_core (const guchar *buf_a,
/* check if the pixels are the same */
if (row_a[x] == row_b[x])
continue;
/* even if they're not literally the same, fully-transparent
* pixels are effectively the same regardless of colour */
if ((row_a[x] & 0xff000000) == 0 && (row_b[x] & 0xff000000) == 0)
continue;
if (diff == NULL)
{
diff = cairo_image_surface_create (CAIRO_FORMAT_RGB24,