From 360e897ccd53bf863cea1ad6184d35e9b6ffbf40 Mon Sep 17 00:00:00 2001
From: Fernando Sahmkow <fsahmkow27@gmail.com>
Date: Sun, 18 Jul 2021 23:06:12 +0200
Subject: [PATCH] ShaderDecompiler: Add initial support for rescaling.

---
 .../ir_opt/rescaling_pass.cpp                 | 72 +++++++++++++++++++
 src/shader_recompiler/shader_info.h           |  1 +
 2 files changed, 73 insertions(+)
 create mode 100644 src/shader_recompiler/ir_opt/rescaling_pass.cpp

diff --git a/src/shader_recompiler/ir_opt/rescaling_pass.cpp b/src/shader_recompiler/ir_opt/rescaling_pass.cpp
new file mode 100644
index 000000000..d3ae3f159
--- /dev/null
+++ b/src/shader_recompiler/ir_opt/rescaling_pass.cpp
@@ -0,0 +1,72 @@
+// Copyright 2021 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "common/alignment.h"
+#include "shader_recompiler/environment.h"
+#include "shader_recompiler/frontend/ir/modifiers.h"
+#include "shader_recompiler/frontend/ir/program.h"
+#include "shader_recompiler/frontend/ir/value.h"
+#include "shader_recompiler/ir_opt/passes.h"
+#include "shader_recompiler/shader_info.h"
+
+namespace Shader::Optimization {
+namespace {
+
+void PatchFragCoord(IR::Inst& inst) {
+    IR::IREmitter ir{block, IR::Block::InstructionList::s_iterator_to(inst)};
+    const IR::F32 inv_resolution_factor = IR::F32{Settings::values.resolution_info.down_factor};
+    const IR::F32 new_get_attribute = ir.GetAttribute(inst.Arg(0).Attribute());
+    const IR::F32 mul = ir.FMul(new_get_attribute, inv_resolution_factor);
+    const IR::U1 should_rescale = IR::U1{true};
+    const IR::F32 selection = ir.Select(should_rescale, mul, new_get_attribute);
+    inst.ReplaceUsesWith(selection);
+}
+
+void Visit(Info& info, IR::Inst& inst) {
+    info.requires_rescaling_uniform = false;
+    switch (inst.GetOpcode()) {
+    case IR::Opcode::GetAttribute: {
+        conast auto attrib = inst.Arg(0).Attribute();
+        const bool is_frag =
+            attrib == IR::Attribute::PositionX || attrib == IR::Attribute::PositionY;
+        const bool must_path = is_frag && program.stage == Stage::Fragment;
+        if (must_path) {
+            PatchFragCoord(inst);
+            info.requires_rescaling_uniform = true;
+        }
+        break;
+    }
+    case IR::Opcode::ImageQueryDimensions: {
+        info.requires_rescaling_uniform |= true;
+        break;
+    }
+    case IR::Opcode::ImageFetch: {
+        info.requires_rescaling_uniform |= true;
+        break;
+    }
+    case IR::Opcode::ImageRead: {
+        info.requires_rescaling_uniform |= true;
+        break;
+    }
+    case IR::Opcode::ImageWrite: {
+        info.requires_rescaling_uniform |= true;
+        break;
+    }
+    default:
+        break;
+    }
+}
+
+} // namespace
+
+void RescalingPass(Environment& env, IR::Program& program) {
+    Info& info{program.info};
+    for (IR::Block* const block : program.post_order_blocks) {
+        for (IR::Inst& inst : block->Instructions()) {
+            Visit(info, inst);
+        }
+    }
+}
+
+} // namespace Shader::Optimization
diff --git a/src/shader_recompiler/shader_info.h b/src/shader_recompiler/shader_info.h
index 4ef4dbd40..e7981a08c 100644
--- a/src/shader_recompiler/shader_info.h
+++ b/src/shader_recompiler/shader_info.h
@@ -172,6 +172,7 @@ struct Info {
     bool uses_global_memory{};
     bool uses_atomic_image_u32{};
     bool uses_shadow_lod{};
+    bool requires_rescaling_uniform{};
 
     IR::Type used_constant_buffer_types{};
     IR::Type used_storage_buffer_types{};