st/mesa: add a fallback for clear_with_quad when no vs_layer

Not all drivers can set gl_Layer from VS. Add a fallback that passes the
instance id from VS to GS, and then uses the GS to set the layer.

Tested by adding

  quad_buffers |= clear_buffers;
  clear_buffers = 0;

to the st_Clear logic, and forcing set_vertex_shader_layered in all
cases. No piglit regressions (on piglits with 'clear' in the name).

Signed-off-by: Ilia Mirkin <[email protected]>
Reviewed-by: Marek Olšák <[email protected]>
Cc: "10.4 10.3" <[email protected]>

0 files changed, 0 insertions, 0 deletions