2 files changed, 78 insertions, 0 deletions

diff --git a/src/shader_recompiler/ir_opt/passes.h b/src/shader_recompiler/ir_opt/passes.h
index 6ff8e4266..24f609d69 100644
--- a/src/shader_recompiler/ir_opt/passes.h
+++ b/src/shader_recompiler/ir_opt/passes.h
@@ -17,6 +17,7 @@ void LowerFp16ToFp32(IR::Program& program);
 void LowerInt64ToInt32(IR::Program& program);
 void RescalingPass(IR::Program& program);
 void SsaRewritePass(IR::Program& program);
+void PositionPass(Environment& env, IR::Program& program);
 void TexturePass(Environment& env, IR::Program& program);
 void VerificationPass(const IR::Program& program);
 
diff --git a/src/shader_recompiler/ir_opt/position_pass.cpp b/src/shader_recompiler/ir_opt/position_pass.cpp
new file mode 100644
index 000000000..3c20b7189
--- /dev/null
+++ b/src/shader_recompiler/ir_opt/position_pass.cpp
@@ -0,0 +1,77 @@
+// SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <boost/container/small_vector.hpp>
+
+#include "shader_recompiler/frontend/ir/basic_block.h"
+#include "shader_recompiler/frontend/ir/ir_emitter.h"
+#include "shader_recompiler/frontend/ir/value.h"
+#include "shader_recompiler/ir_opt/passes.h"
+
+namespace Shader::Optimization {
+
+namespace {
+struct PositionInst {
+    IR::Inst* inst;
+    IR::Block* block;
+    IR::Attribute attr;
+};
+using PositionInstVector = boost::container::small_vector<PositionInst, 24>;
+} // Anonymous namespace
+
+void PositionPass(Environment& env, IR::Program& program) {
+    if (env.ShaderStage() != Stage::VertexB || env.ReadViewportTransformState()) {
+        return;
+    }
+
+    Info& info{program.info};
+    info.uses_render_area = true;
+
+    PositionInstVector to_replace;
+    for (IR::Block* const block : program.post_order_blocks) {
+        for (IR::Inst& inst : block->Instructions()) {
+            switch (inst.GetOpcode()) {
+            case IR::Opcode::SetAttribute: {
+                const IR::Attribute attr{inst.Arg(0).Attribute()};
+                switch (attr) {
+                case IR::Attribute::PositionX:
+                case IR::Attribute::PositionY: {
+                    to_replace.push_back(PositionInst{.inst = &inst, .block = block, .attr = attr});
+                    break;
+                }
+                default:
+                    break;
+                }
+                break;
+            }
+            default:
+                break;
+            }
+        }
+    }
+
+    for (PositionInst& position_inst : to_replace) {
+        IR::IREmitter ir{*position_inst.block,
+                         IR::Block::InstructionList::s_iterator_to(*position_inst.inst)};
+        const IR::F32 value(position_inst.inst->Arg(1));
+        const IR::F32F64 scale(ir.Imm32(2.f));
+        const IR::F32 negative_one{ir.Imm32(-1.f)};
+        switch (position_inst.attr) {
+        case IR::Attribute::PositionX: {
+            position_inst.inst->SetArg(
+                1,
+                ir.FPFma(value, ir.FPMul(ir.FPRecip(ir.RenderAreaWidth()), scale), negative_one));
+            break;
+        }
+        case IR::Attribute::PositionY: {
+            position_inst.inst->SetArg(
+                1,
+                ir.FPFma(value, ir.FPMul(ir.FPRecip(ir.RenderAreaHeight()), scale), negative_one));
+            break;
+        }
+        default:
+            break;
+        }
+    }
+}
+} // namespace Shader::Optimization