Bug 48678

Summary:	gl_PointCoord delivering wrong values
Product:	Mesa	Reporter:	Lucas <lvella>
Component:	Drivers/DRI/i965	Assignee:	Ian Romanick <idr>
Status:	RESOLVED FIXED	QA Contact:
Severity:	normal
Priority:	medium
Version:	git
Hardware:	x86 (IA32)
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:
Attachments:	Program that triggers the problem. Intel rendering (just a black screen). Radeon rendering (correct, a bluish ball)

Description Lucas 2012-04-13 23:07:31 UTC

When rendering point sprites, the value delivered to the gl_PointCoord special variable in the fragment shader is wrong; probably uninitialized data.

Attached there is a small program that triggers the problem, and an screenshot taken on a Intel® GM45 (incorrect rendering) and another taken on a Radeon R700 (correct rendering), both under Mesa.

Compile the program with:
$ cc -o ball ball.c -lglut -lGLEW -lm

Comment 1 Lucas 2012-04-13 23:09:38 UTC

Created attachment 59958 [details]
Program that triggers the problem.

Comment 2 Lucas 2012-04-13 23:11:11 UTC

Created attachment 59959 [details]
Intel rendering (just a black screen).

Comment 3 Lucas 2012-04-13 23:13:49 UTC

Created attachment 59960 [details]
Radeon rendering (correct, a bluish ball)

Comment 4 Lucas 2012-04-13 23:15:47 UTC

Bug #43580 is probably related.

Comment 5 Lucas 2012-04-14 09:47:24 UTC

New info, the problem seems to be restricted to some devices. The problem is present on the following renderer/software:

OpenGL vendor string: Tungsten Graphics, Inc
OpenGL renderer string: Mesa DRI Mobile Intel® GM45 Express Chipset x86/MMX/SSE2
OpenGL version string: 2.1 Mesa 8.1-devel (git-897af1d oneiric-oibaf-ppa)
OpenGL shading language version string: 1.20


While in the following renderer/software, the sample program renders fine:

OpenGL vendor string: Tungsten Graphics, Inc
OpenGL renderer string: Mesa DRI Intel(R) Sandybridge Mobile 
OpenGL version string: 2.1 Mesa 7.11
OpenGL shading language version string: 1.20

Comment 6 Eric Anholt 2012-08-13 05:39:48 UTC

commit 43af02ac731dac7d80f7e47feb0c80e4da156769
Author: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Date:   Mon Feb 27 15:46:32 2012 +0800

    i965: handle gl_PointCoord for Gen4 and Gen5 platforms

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