[Bug 102678] gl_BaseVertex should always be zero when the draw command has no <basevertex> parameter

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=102678

            Bug ID: 102678
           Summary: gl_BaseVertex should always be zero when the draw
                    command has no <basevertex> parameter
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: intel-3d-bugs at lists.freedesktop.org
          Reporter: apuentes at igalia.com
        QA Contact: intel-3d-bugs at lists.freedesktop.org

Hardware: Broadwell or Skylake
Mesa commit: f940b1665a7f17ad2ae7ae2e951d90d151482875
vk-gl-cts commit: dfcb8e870438f6f2bfe71d4bb63d43120debb3a3

The following ARB_shader_draw_parameters tests fail: 

* KHR-GL45.shader_draw_parameters_tests.ShaderDrawArraysParameters
* KHR-GL45.shader_draw_parameters_tests.ShaderDrawArraysInstancedParameters
* KHR-GL45.shader_draw_parameters_tests.ShaderMultiDrawArraysParameters
* KHR-GL45.shader_draw_parameters_tests.ShaderMultiDrawArraysIndirectParameters

- Expected outcome:

The tests expect gl_BaseVertex to be zero when the draw command does not accept
a <basevertex> parameter. 

>From the ARB_shader_draw_parameters specification:
 "<gl_BaseVertexARB> holds the integer value passed to the <baseVertex>
 parameter to the command that resulted in the current shader invocation.
 In the case where the command has no <baseVertex> parameter, the value
 of <gl_BaseVertexARB> is zero."

- Actual outcome:

Although non-indexed draw commands like gl*DrawArrays* do not accept
<basevertex> parameters, Mesa sets the value of gl_BaseVertex to the value
passed to the <first> parameter of the gl*DrawArrays* command instead of
setting it to zero.

Indexed draw calls like glDrawElements which do not accept a <basevertex>
parameter work as expected, gl_BaseVertex is zero in that case.

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