i965: Implement ARB_fragment_layer_viewport.
Normally, we could read gl_Layer from bits 26:16 of R0.0. However, the specification requires that bogus out-of-range 32-bit values written by previous stages need to appear in the fragment shader as-written. Instead, we pass in the full 32-bit value from the VUE header as an extra flat-shaded varying. We have the SF override the value to 0 when the previous stage didn't actually write a value (it's actually defined to return 0). Signed-off-by: Kenneth Graunke <email@example.com> Reviewed-by: Chris Forbes <firstname.lastname@example.org>
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