From 6c512f4bffde6bd8e4dbc74ed27cc84cd7fffadb Mon Sep 17 00:00:00 2001
From: ameerj <52414509+ameerj@users.noreply.github.com>
Date: Wed, 14 Apr 2021 00:32:18 -0400
Subject: spirv: Implement alpha test

---
 .../backend/spirv/emit_spirv_special.cpp           | 45 ++++++++++++++++++++++
 1 file changed, 45 insertions(+)

(limited to 'src/shader_recompiler/backend/spirv')

diff --git a/src/shader_recompiler/backend/spirv/emit_spirv_special.cpp b/src/shader_recompiler/backend/spirv/emit_spirv_special.cpp
index 7af29e4dd..8bb94f546 100644
--- a/src/shader_recompiler/backend/spirv/emit_spirv_special.cpp
+++ b/src/shader_recompiler/backend/spirv/emit_spirv_special.cpp
@@ -37,6 +37,48 @@ Id DefaultVarying(EmitContext& ctx, u32 num_components, u32 element, Id zero, Id
     }
     throw InvalidArgument("Bad element");
 }
+
+Id ComparisonFunction(EmitContext& ctx, CompareFunction comparison, Id operand_1, Id operand_2) {
+    switch (comparison) {
+    case CompareFunction::Never:
+        return ctx.false_value;
+    case CompareFunction::Less:
+        return ctx.OpFOrdLessThan(ctx.U1, operand_1, operand_2);
+    case CompareFunction::Equal:
+        return ctx.OpFOrdEqual(ctx.U1, operand_1, operand_2);
+    case CompareFunction::LessThanEqual:
+        return ctx.OpFOrdLessThanEqual(ctx.U1, operand_1, operand_2);
+    case CompareFunction::Greater:
+        return ctx.OpFOrdGreaterThan(ctx.U1, operand_1, operand_2);
+    case CompareFunction::NotEqual:
+        return ctx.OpFOrdNotEqual(ctx.U1, operand_1, operand_2);
+    case CompareFunction::GreaterThanEqual:
+        return ctx.OpFOrdGreaterThanEqual(ctx.U1, operand_1, operand_2);
+    case CompareFunction::Always:
+        return ctx.true_value;
+    }
+    throw InvalidArgument("Comparison function {}", comparison);
+}
+
+void AlphaTest(EmitContext& ctx) {
+    const auto comparison{*ctx.profile.alpha_test_func};
+    if (comparison == CompareFunction::Always) {
+        return;
+    }
+    const Id type{ctx.F32[1]};
+    const Id rt0_color{ctx.OpLoad(ctx.F32[4], ctx.frag_color[0])};
+    const Id alpha{ctx.OpCompositeExtract(type, rt0_color, 3u)};
+
+    const Id true_label{ctx.OpLabel()};
+    const Id discard_label{ctx.OpLabel()};
+    const Id alpha_reference{ctx.Constant(ctx.F32[1], ctx.profile.alpha_test_reference)};
+    const Id condition{ComparisonFunction(ctx, comparison, alpha, alpha_reference)};
+
+    ctx.OpBranchConditional(condition, true_label, discard_label);
+    ctx.AddLabel(discard_label);
+    ctx.OpKill();
+    ctx.AddLabel(true_label);
+}
 } // Anonymous namespace
 
 void EmitPrologue(EmitContext& ctx) {
@@ -68,6 +110,9 @@ void EmitEpilogue(EmitContext& ctx) {
     if (ctx.stage == Stage::VertexB && ctx.profile.convert_depth_mode) {
         ConvertDepthMode(ctx);
     }
+    if (ctx.stage == Stage::Fragment) {
+        AlphaTest(ctx);
+    }
 }
 
 void EmitEmitVertex(EmitContext& ctx, const IR::Value& stream) {
-- 
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