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<body><span class="vcard"><a class="email" href="mailto:danylo.piliaiev@gmail.com" title="Danylo <danylo.piliaiev@gmail.com>"> <span class="fn">Danylo</span></a>
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<a class="bz_bug_link
bz_status_NEW "
title="NEW - Fractional viewport coordinates shift viewport corner by a whole integer"
href="https://bugs.freedesktop.org/show_bug.cgi?id=106526">bug 106526</a>
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<td>danylo.piliaiev@gmail.com
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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - Fractional viewport coordinates shift viewport corner by a whole integer"
href="https://bugs.freedesktop.org/show_bug.cgi?id=106526#c1">Comment # 1</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - Fractional viewport coordinates shift viewport corner by a whole integer"
href="https://bugs.freedesktop.org/show_bug.cgi?id=106526">bug 106526</a>
from <span class="vcard"><a class="email" href="mailto:danylo.piliaiev@gmail.com" title="Danylo <danylo.piliaiev@gmail.com>"> <span class="fn">Danylo</span></a>
</span></b>
<pre>There is a similar bug filed for Nvidia driver
<a href="https://devtalk.nvidia.com/default/topic/971005/linux/glviewportindexedf-wrongly-rounding-down-x-and-y-parameters/">https://devtalk.nvidia.com/default/topic/971005/linux/glviewportindexedf-wrongly-rounding-down-x-and-y-parameters/</a>
.
I wasn't able to find the exact specification for such case but e.g. Wine
expects coordinates not to be shifted (see
wined3d_caps_gl_ctx_test_viewport_subpixel_bits function in Wine).
The closest line in specs is in the specification of ARB_viewport_array
extension:
<span class="quote">> Direct3D 11 specifies that rasterization along the one-pixel edges of</span >
fractional viewports to be undefined. If implementations want defined
behavior with fractional viewports, they can program a slightly wider viewport
and scissor away the pixels along the edge of the expanded viewport.
Viewport's width and height is already ceiled on radeon driver and i965 behaves
the same before gen8.
I've made and sent the patch to fix the issue.</pre>
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