Bug 10571

Summary:	[PATCH] Line clipping sometimes produces unexpected results
Product:	Mesa	Reporter:	David Moore <dcm>
Component:	Drivers/DRI/i965	Assignee:	Eric Anholt <eric>
Status:	RESOLVED FIXED	QA Contact:
Severity:	normal
Priority:	medium
Version:	git
Hardware:	x86-64 (AMD64)
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:
Attachments:	Patch to correct line clipping for i965 Test case that demonstrates the missing lines

Description David Moore 2007-04-08 16:24:51 UTC

When drawing long lines that extend well off the edge of the screen, some of these lines disappear completely instead of being clipped in the usual way.

I am using a G965 with the latest git version of Mesa DRI.

The problem seems to lie in the generated clip program.  In the case that _both_ dot products are positive (meaning that the line should not be clipped against that particular plane), an erroneous clip is sometimes generated.

Comment 1 David Moore 2007-04-08 16:28:43 UTC

Created attachment 9518 [details] [review]
Patch to correct line clipping for i965

I see some chatter about a "-ve rhw" workaround in the code that might have something to do with this bug.  Regardless, the attached patch seems to work.

Comment 2 David Moore 2007-08-08 00:03:46 UTC

Created attachment 11044 [details]
Test case that demonstrates the missing lines

Here is a sample program that demonstrates the bug.  This program draws 10 long lines at a slightly askew angle.  However, only 7 lines appear on screen.  If the angle of the glRotatef() command is modified slightly, all 10 lines will appear.  I would be very appreciative if an engineer from Intel could try to reproduce this on their end.  Thanks.

Comment 3 Michael Fu 2007-08-27 17:56:30 UTC

Eric, would you please review the patch?

Comment 4 Eric Anholt 2007-08-30 14:44:59 UTC

Committed.  Thanks!

Comment 5 Adam Jackson 2009-08-24 12:26:23 UTC

Mass version move, cvs -> git

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