[Bug 109451] [IVB] LINE_STRIPs following a TRIANGLE_FAN fail to use primitive restart
bugzilla-daemon at freedesktop.org
bugzilla-daemon at freedesktop.org
Thu Jan 24 19:33:51 UTC 2019
https://bugs.freedesktop.org/show_bug.cgi?id=109451
Bug ID: 109451
Summary: [IVB] LINE_STRIPs following a TRIANGLE_FAN fail to use
primitive restart
Product: Mesa
Version: 18.3
Hardware: x86-64 (AMD64)
OS: Linux (All)
Status: NEW
Severity: normal
Priority: medium
Component: Drivers/DRI/i965
Assignee: intel-3d-bugs at lists.freedesktop.org
Reporter: perso at elementw.net
QA Contact: intel-3d-bugs at lists.freedesktop.org
Created attachment 143227
--> https://bugs.freedesktop.org/attachment.cgi?id=143227&action=edit
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.
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