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<base href="https://bugs.freedesktop.org/" />
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<th>Priority</th>
<td>medium
</td>
</tr>
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - test/cairo-test-suite reports wrong max diff comparing different opaque images"
href="https://bugs.freedesktop.org/show_bug.cgi?id=84044">84044</a>
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<th>Assignee</th>
<td>chris@chris-wilson.co.uk
</td>
</tr>
<tr>
<th>Summary</th>
<td>test/cairo-test-suite reports wrong max diff comparing different opaque images
</td>
</tr>
<tr>
<th>QA Contact</th>
<td>cairo-bugs@cairographics.org
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
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<th>Reporter</th>
<td>sixtysix@inwind.it
</td>
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<tr>
<th>Hardware</th>
<td>Other
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
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<th>Component</th>
<td>general
</td>
</tr>
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<th>Product</th>
<td>cairo
</td>
</tr></table>
<p>
<div>
<pre>In test/buffer-diff.c (line 80), when two pixels differ, all channels
are considered to compute result.max_diff, this means in the case of
rgb24 images also the meaningless alpha channel.
Similarly pdiff_compare in test/pdiff/pdiff.c uses the (non)alpha
channel to unpremultiply the not premultiplied rgb channels, hardly
giving the expected results.
Probably there should be a test-suite for pdiff to check for false
positive/negative.
This results in many image.rgb24 failures that would be accepted
using the same criterion used for image.argb32 target making the
cairo test-suite output quite confusing.
BTW to slightly speed up the test-suite you could write and use a
'pdiff_compare_fast' that returns 1 the first time pixels_failed is
incremented.
The best way to speed up the test-suite is to have all tests PASS though.</pre>
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