Bug 15444 - [OGL] Draw polygon has one pixel bias if PolygonMode is GL_LINE
[OGL] Draw polygon has one pixel bias if PolygonMode is GL_LINE
Status: RESOLVED NOTABUG
Product: Mesa
Classification: Unclassified
Component: Drivers/DRI/i915
unspecified
x86 (IA32) Linux (All)
: medium minor
Assigned To: haihao
:
Depends on:
Blocks: intel-3d-release
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Reported: 2008-04-11 00:20 UTC by WuNian
Modified: 2009-05-20 20:54 UTC (History)
1 user (show)

See Also:


Attachments
test case (1.65 KB, text/plain)
2008-04-13 22:44 UTC, WuNian
Details

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Description WuNian 2008-04-11 00:20:38 UTC
If draw a polygon with depth value, then read it back, there is one pixel bias.

Please see bug #15194 comment6.
http://bugs.freedesktop.org/show_bug.cgi?id=15194#c6

The bug exists on both i915 and i965.
Comment 1 WuNian 2008-04-13 22:42:53 UTC
The bug results from the PolygonMode is set as GL_LINE.
If set the PolygonMode as GL_LINE, then polygon will be drawn with one pixel bias(only the left line).
Comment 2 WuNian 2008-04-13 22:44:47 UTC
Created attachment 15888 [details]
test case
Comment 3 Eric Anholt 2009-05-20 20:54:48 UTC
The spec allows the line rasterization to be off by a pixel in X or Y.  But in the case of this test, the lines are being drawn exactly on the pixel boundaries, so if the test was fixed to draw the lines along the middle of the pixels, it would work fine on our hardware (and probably everyone else's, too).