From b90c15919b0334a34c80b7f52d29f060699a54a3 Mon Sep 17 00:00:00 2001
From: offtkp <parisoplop@gmail.com>
Date: Sun, 21 Jul 2024 16:32:45 +0300
Subject: [PATCH] Shadergen fog

---
 include/PICA/pica_frag_config.hpp | 21 ++++++++++++++++++++-
 include/PICA/regs.hpp             |  6 ++++++
 include/PICA/shader_gen.hpp       |  2 ++
 src/core/PICA/shader_gen_glsl.cpp | 25 +++++++++++++++++++++++++
 4 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/include/PICA/pica_frag_config.hpp b/include/PICA/pica_frag_config.hpp
index f4142ef1..32fa7aa6 100644
--- a/include/PICA/pica_frag_config.hpp
+++ b/include/PICA/pica_frag_config.hpp
@@ -29,6 +29,18 @@ namespace PICA {
 		std::array<u32, 4 * 6> tevConfigs;
 	};
 
+	struct FogConfig {
+		union {
+			u32 raw{};
+
+			BitField<0, 3, FogMode> mode;
+			BitField<3, 1, u32> flipDepth;
+			BitField<8, 8, u32> fogColorR;
+			BitField<16, 8, u32> fogColorG;
+			BitField<24, 8, u32> fogColorB;
+		};
+	};
+
 	struct Light {
 		union {
 			u16 raw;
@@ -189,6 +201,7 @@ namespace PICA {
 	struct FragmentConfig {
 		OutputConfig outConfig;
 		TextureConfig texConfig;
+		FogConfig fogConfig;
 		LightingConfig lighting;
 
 		bool operator==(const FragmentConfig& config) const {
@@ -220,12 +233,18 @@ namespace PICA {
 			setupTevStage(4);
 			setupTevStage(5);
 #undef setupTevStage
+
+			fogConfig.mode = (FogMode)Helpers::getBits<0, 3>(regs[InternalRegs::TexEnvUpdateBuffer]);
+			fogConfig.flipDepth = Helpers::getBit<16>(regs[InternalRegs::TexEnvUpdateBuffer]);
+			fogConfig.fogColorR = Helpers::getBits<0, 8>(regs[InternalRegs::FogColor]);
+			fogConfig.fogColorG = Helpers::getBits<8, 8>(regs[InternalRegs::FogColor]);
+			fogConfig.fogColorB = Helpers::getBits<16, 8>(regs[InternalRegs::FogColor]);
 		}
 	};
 
 	static_assert(
 		std::has_unique_object_representations<OutputConfig>() && std::has_unique_object_representations<TextureConfig>() &&
-		std::has_unique_object_representations<Light>()
+		std::has_unique_object_representations<FogConfig>() && std::has_unique_object_representations<Light>()
 	);
 }  // namespace PICA
 
diff --git a/include/PICA/regs.hpp b/include/PICA/regs.hpp
index c66c90ca..636e8f7c 100644
--- a/include/PICA/regs.hpp
+++ b/include/PICA/regs.hpp
@@ -396,6 +396,12 @@ namespace PICA {
 		GreaterOrEqual = 7,
 	};
 
+	enum class FogMode : u32 {
+		Disabled = 0,
+		Fog = 5,
+		Gas = 7,
+	};
+
 	struct TexEnvConfig {
 		enum class Source : u8 {
 			PrimaryColor = 0x0,
diff --git a/include/PICA/shader_gen.hpp b/include/PICA/shader_gen.hpp
index 085d990a..215e5adb 100644
--- a/include/PICA/shader_gen.hpp
+++ b/include/PICA/shader_gen.hpp
@@ -24,6 +24,8 @@ namespace PICA::ShaderGen {
 		void compileLUTLookup(std::string& shader, const PICA::FragmentConfig& config, u32 lightIndex, u32 lutID);
 		bool isSamplerEnabled(u32 environmentID, u32 lutID);
 
+		void compileFog(std::string& shader, const PICA::FragmentConfig& config);
+
 	  public:
 		FragmentGenerator(API api, Language language) : api(api), language(language) {}
 		std::string generate(const PICA::FragmentConfig& config);
diff --git a/src/core/PICA/shader_gen_glsl.cpp b/src/core/PICA/shader_gen_glsl.cpp
index 01210587..9802be90 100644
--- a/src/core/PICA/shader_gen_glsl.cpp
+++ b/src/core/PICA/shader_gen_glsl.cpp
@@ -194,6 +194,8 @@ std::string FragmentGenerator::generate(const FragmentConfig& config) {
 		compileTEV(ret, i, config);
 	}
 
+	compileFog(ret, config);
+
 	applyAlphaTest(ret, config);
 
 	ret += "fragColor = combinerOutput;\n}"; // End of main function
@@ -652,4 +654,27 @@ void FragmentGenerator::compileLUTLookup(std::string& shader, const PICA::Fragme
 			shader += "lut_lookup_result *= " + std::to_string(scales[scale]) + ";\n";
 		}
 	}
+}
+
+void FragmentGenerator::compileFog(std::string& shader, const PICA::FragmentConfig& config) {
+	if (config.fogConfig.mode != FogMode::Fog) {
+		return;
+	}
+
+	float r = config.fogConfig.fogColorR / 255.0f;
+	float g = config.fogConfig.fogColorG / 255.0f;
+	float b = config.fogConfig.fogColorB / 255.0f;
+
+	if (config.fogConfig.flipDepth) {
+		shader += "float fog_index = (1.0 - depth) * 128.0;\n";
+	} else {
+		shader += "float fog_index = depth * 128.0;\n";
+	}
+
+	shader += "float clamped_index = clamp(floor(fog_index), 0.0, 127.0);";
+	shader += "float delta = fog_index - clamped_index;";
+	shader += "vec3 fog_color = vec3(" + std::to_string(r) + ", " + std::to_string(g) + ", " + std::to_string(b) + ");";
+	shader += "vec2 value = texelFetch(u_tex_luts, ivec2(int(clamped_index), 24), 0).rg;"; // fog LUT is past the light LUTs
+	shader += "float fog_factor = clamp(value.r + value.g * delta, 0.0, 1.0);";
+	shader += "combinerOutput.rgb = mix(fog_color, combinerOutput.rgb, fog_factor);";
 }
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