Bug 48678 - gl_PointCoord delivering wrong values
gl_PointCoord delivering wrong values
Status: RESOLVED FIXED
Product: Mesa
Classification: Unclassified
Component: Drivers/DRI/i965
git
x86 (IA32) Linux (All)
: medium normal
Assigned To: Ian Romanick
:
Depends on:
Blocks:
  Show dependency treegraph
 
Reported: 2012-04-13 23:07 UTC by Lucas
Modified: 2012-08-13 05:39 UTC (History)
0 users

See Also:


Attachments
Program that triggers the problem. (2.66 KB, text/x-csrc)
2012-04-13 23:09 UTC, Lucas
Details
Intel rendering (just a black screen). (9.93 KB, image/png)
2012-04-13 23:11 UTC, Lucas
Details
Radeon rendering (correct, a bluish ball) (13.71 KB, image/png)
2012-04-13 23:13 UTC, Lucas
Details

Note You need to log in before you can comment on or make changes to this bug.
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