nir: Move vc4's alpha test lowering to core NIR.

I've been doing this inside of vc4, but vc5 wants it as well and it may be
useful for other drivers (Intel has a related path for pre-gen6 with MRT,
and freedreno had a TGSI path for it at one point).

This required defining a common enum for the standard comparison
functions, but other lowering passes are likely to also want that enum.

v2: Add to meson.build as well.

Acked-by: Rob Clark <[email protected]>

1 files changed, 11 insertions, 4 deletions

diff --git a/src/gallium/drivers/vc4/vc4_program.c b/src/gallium/drivers/vc4/vc4_program.c
index e93333d35e7..bf7424bf28a 100644
--- a/src/gallium/drivers/vc4/vc4_program.c
+++ b/src/gallium/drivers/vc4/vc4_program.c
@@ -2250,8 +2250,15 @@ vc4_shader_ntq(struct vc4_context *vc4, enum qstage stage,
 
         c->s = nir_shader_clone(c, key->shader_state->base.ir.nir);
 
-        if (stage == QSTAGE_FRAG)
+        if (stage == QSTAGE_FRAG) {
+                if (c->fs_key->alpha_test_func != COMPARE_FUNC_ALWAYS) {
+                        NIR_PASS_V(c->s, nir_lower_alpha_test,
+                                   c->fs_key->alpha_test_func,
+                                   c->fs_key->sample_alpha_to_one &&
+                                   c->fs_key->msaa);
+                }
                 NIR_PASS_V(c->s, vc4_nir_lower_blend, c);
+        }
 
         struct nir_lower_tex_options tex_options = {
                 /* We would need to implement txs, but we don't want the
@@ -2748,10 +2755,10 @@ vc4_update_compiled_fs(struct vc4_context *vc4, uint8_t prim_mode)
         key->stencil_full_writemasks = vc4->zsa->stencil_uniforms[2] != 0;
         key->depth_enabled = (vc4->zsa->base.depth.enabled ||
                               key->stencil_enabled);
-        if (vc4->zsa->base.alpha.enabled) {
-                key->alpha_test = true;
+        if (vc4->zsa->base.alpha.enabled)
                 key->alpha_test_func = vc4->zsa->base.alpha.func;
-        }
+        else
+                key->alpha_test_func = COMPARE_FUNC_ALWAYS;
 
         if (key->is_points) {
                 key->point_sprite_mask =