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scaling test: Avoid dividing zero by zero

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If all four of the random colours have alpha channel exactly 0.0,
then the computed premultiplied average will also be zero.
Normalize the expected colour to (0,0,0,0) rather than (NaN,NaN,NaN,0).

Resolves: https://gitlab.gnome.org/GNOME/gtk/-/issues/6977
Signed-off-by: Simon McVittie <smcv@debian.org>
This commit is contained in:
Simon McVittie 2024-09-03 00:12:48 +01:00
parent 6e54589d9e
commit 4c4d260199
1 changed files with 16 additions and 4 deletions
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20
testsuite/gsk/scaling.c
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@ -896,10 +896,22 @@ create_stipple_texture (GdkMemoryFormat format,
}
}
average->red /= average->alpha;
average->green /= average->alpha;
average->blue /= average->alpha;
average->alpha /= 4.0f;
if (average->alpha != 0.0f)
{
average->red /= average->alpha;
average->green /= average->alpha;
average->blue /= average->alpha;
average->alpha /= 4.0f;
}
else
{
/* Each component of the average has been multiplied by the alpha
* already, so if the alpha is zero, all components should also
* be zero */
g_assert_cmpfloat (average->red, ==, 0.0f);
g_assert_cmpfloat (average->green, ==, 0.0f);
g_assert_cmpfloat (average->blue, ==, 0.0f);
}
texture_builder_init (&builder, format, width, height);
for (y = 0; y < height; y++)