Bug 15444

Summary: [OGL] Draw polygon has one pixel bias if PolygonMode is GL_LINE
Product: Mesa Reporter: WuNian <nian.wu>
Component: Drivers/DRI/i915Assignee: haihao <haihao.xiang>
Status: RESOLVED NOTABUG QA Contact:
Severity: minor    
Priority: medium CC: dri-devel
Version: unspecified   
Hardware: x86 (IA32)   
OS: Linux (All)   
Whiteboard:
i915 platform: i915 features:
Bug Depends on:    
Bug Blocks: 20277    
Attachments: test case

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).

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