[Bug 109451] [IVB] LINE_STRIPs following a TRIANGLE_FAN fail to use primitive restart

[bugzilla-daemon at freedesktop.org]

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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