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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - dEQP-GLES3: incorrect wide line rasterization after clipping"
href="https://bugs.freedesktop.org/show_bug.cgi?id=89650">89650</a>
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<th>Summary</th>
<td>dEQP-GLES3: incorrect wide line rasterization after clipping
</td>
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<th>Product</th>
<td>Mesa
</td>
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<th>Version</th>
<td>git
</td>
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<th>Hardware</th>
<td>Other
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>medium
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<th>Component</th>
<td>Drivers/DRI/i965
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<th>Assignee</th>
<td>idr@freedesktop.org
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<th>Reporter</th>
<td>itoral@igalia.com
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<th>QA Contact</th>
<td>intel-3d-bugs@lists.freedesktop.org
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<p>
<div>
<pre>Affected tests:
dEQP-GLES3.functional.rasterization.primitives.line_strip_wide
dEQP-GLES3.functional.rasterization.primitives.line_loop_wide
In these cases it looks like one of the edges of a line is outside the viewport
(right end of the viewport). The hardware seems to clip using the rightmost
edge of the line as reference, but this means that the leftmost side is clipped
before it should according to dEQP.
Enabling the guardand test in gen7 fixes this, but a comment in the code
suggests that we should not do this to prevent rendering to the underlying
surface outside the viewport region (gen8 hw fixes this apparently), so if the
guardband is not disabled for this case in gen8 this may be fixed for gen8+.
The OpenGL spec is not clear as to how clipping should work with wide lines,
but it suggests that for xmajor lines, columns of pixels should be rendered,
and that is not what is happening here (but that section does not consider
clipping to any extent). Some texts seem to suggest that OpenGL expects wide
lines to be rendered as multiple width=1 lines. If this is the case, then deqp
is right and intel rendering is bogus (intel renders a paralelogram), but
nothing in the OpenGL spec seems to make this clear. I think clipping with wide
lines is not clearly specified.
So this might be a bogus tests or incorrect. We had some discussion on this
topic in the mailing list:
<a href="http://lists.freedesktop.org/archives/mesa-dev/2015-February/076072.html">http://lists.freedesktop.org/archives/mesa-dev/2015-February/076072.html</a>
Although I don't think there is a clear conclusion I believe that the spirit of
the spec is the one represented by dEQP expectations.</pre>
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