Bug 109451

Summary:	[IVB,SNB] LINE_STRIPs following a TRIANGLE_FAN fail to use primitive restart
Product:	Mesa	Reporter:	Dorian Wouters <perso>
Component:	Drivers/DRI/i965	Assignee:	Intel 3D Bugs Mailing List <intel-3d-bugs>
Status:	RESOLVED FIXED	QA Contact:	Intel 3D Bugs Mailing List <intel-3d-bugs>
Severity:	normal
Priority:	medium
Version:	18.3
Hardware:	x86-64 (AMD64)
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:
Attachments:	apitrace of example program test program source code Mesa patch v1

Description Dorian Wouters 2019-01-24 19:33:51 UTC

Created attachment 143227 [details]
apitrace of example program

Originally reported as a Blender bug: https://developer.blender.org/T60762
(which it is not)

Using desktop GL 3.3+.

Steps to reproduce:
* prepare a vertex and index buffer
* enable GL_PRIMITIVE_RESTART
* draw a GL_TRIANGLE_FAN using those buffers
* draw any number of GL_LINE_STRIPs with those same buffers

Drawing a GL_TRIANGLE_FAN prior to GL_LINE_STRIPs makes the strip draw calls fail to use restart markers (here, 0xFF), resulting in the line strips' supposedly unconnected strips being connected through a point of invalid coordinates (observed to consistently be (0, 0, 0)).
IOW, restart markers seems to be (re-)considered as normal indices.

Interfering with GL calls that read or write to the index buffer makes the problem go away, hinting at a GL state tracking or cache issue.

Comment 1 Dorian Wouters 2019-01-24 19:34:19 UTC

Created attachment 143228 [details]
test program source code

Comment 2 Denis 2019-01-25 08:25:00 UTC

Hi Dorian. Thanks for the report.
I reproduced issue using provided app.
Results:

Ivi bridge - reproduced on 11.0.0, 17.0.0, 18.3.0, 18.3.2, 19.0.0 git latest

But didn't reproduce on KBL with 18.1.5

Investigating

Comment 3 asimiklit 2019-01-25 15:03:07 UTC

I managed to reproduce this issue on SNB using the latest git mesa.
I am going to continue my investigation)

Comment 4 asimiklit 2019-01-28 15:07:45 UTC

I found out the root cause of the issue. Unfortunately the issue is in mesa. I have been working on a mesa patch and a piglit test for this issue.

Comment 5 asimiklit 2019-01-30 10:52:21 UTC

Created attachment 143256 [details] [review]
Mesa patch v1

Could you please check this mesa patch with this issue if it is possible and confirm if it helps you.

Thanks,
Andrii

Comment 6 asimiklit 2019-02-01 09:40:19 UTC

I reproduce this issue on KBL using the following test:
https://gitlab.freedesktop.org/asimiklit/piglit/commit/118f0999918f67230ab79780186a1c15febafb3b

The solution was suggested:
https://gitlab.freedesktop.org/mesa/mesa/merge_requests/176

Comment 7 Lionel Landwerlin 2019-02-20 19:50:13 UTC

Fixed with :

commit f4f4ec941e1427142656e588244f378e469e996e (HEAD -> master, origin/master)
Author: Andrii Simiklit <andrii.simiklit@globallogic.com>
Date:   Fri Jan 25 15:03:07 2019 +0200

    i965: re-emit index buffer state on a reset option change.
    
    Seems like we forget to update the index buffer (ib) status and
    IndexedDrawCutIndexEnable or CutIndexEnable flag is left unchanged it
    leads to ignoring of glEnable/glDisable functions for GL_PRIMITIVE_RESTART
    in some cases. The index buffer (ib) status should be re-emmited after the
    reset option change to avoid some unexpected behavior.
    
    Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109451
    Cc: <mesa-stable@lists.freedesktop.org>
    Signed-off-by: Andrii Simiklit <andrii.simiklit@globallogic.com>
    Signed-off-by: Andrii Simiklit <asimiklit.work@gmail.com>

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