From 8f016b10957e7765182cb9e7b2bce0f145548e43 Mon Sep 17 00:00:00 2001
From: Riyyi <riyyi3@gmail.com>
Date: Fri, 14 Oct 2022 23:24:16 +0200
Subject: [PATCH] Emulator: Add function to fetch pixel color from palette

---
 src/emu.h   |  7 ++++++
 src/ppu.cpp | 63 ++++++++++++++++++++++++++++++-----------------------
 src/ppu.h   | 12 ++++++++--
 3 files changed, 53 insertions(+), 29 deletions(-)

diff --git a/src/emu.h b/src/emu.h
index 27603dd..0b1dfca 100644
--- a/src/emu.h
+++ b/src/emu.h
@@ -30,6 +30,11 @@ class Emu final : public ruc::Singleton<Emu> {
 public:
 	Emu(s) {}
 
+	enum Mode : uint8_t {
+		DMG, // Game Boy
+		CGB, // Game Boy Color
+	};
+
 	void init(uint32_t frequency);
 
 	void update();
@@ -43,10 +48,12 @@ public:
 
 	// -------------------------------------
 
+	Mode mode() const { return m_mode; }
 	std::shared_ptr<ProcessingUnit> processingUnit(std::string_view name) const { return m_processing_units.at(name); }
 	MemorySpace memorySpace(std::string_view name) { return m_memory_spaces[name]; }
 
 private:
+	Mode m_mode { Mode::DMG };
 	uint32_t m_frequency { 0 };
 	double m_timestep { 0 };
 	uint32_t m_cycle { 0 };
diff --git a/src/ppu.cpp b/src/ppu.cpp
index 943e4c7..a7fb1ad 100644
--- a/src/ppu.cpp
+++ b/src/ppu.cpp
@@ -120,12 +120,9 @@ void PPU::render()
 		bool tile_data_mode = lcd_control & LCDC::BGandWindowTileDataArea;
 		uint32_t tile_data_address = (tile_data_mode) ? 0x8000 : 0x8800;
 
-		// Pallete
-		uint8_t bg_palette = Emu::the().readMemory(0xff47) & 0xff;
-
 		for (uint32_t i = 0; i < tile_map_size; ++i) {
 			uint8_t tile_index = Emu::the().readMemory(bg_tile_map_address + i);
-			drawTile((i % 32) * TILE_WIDTH, (i / 32) * TILE_HEIGHT, tile_data_address + (tile_index * TILE_SIZE), bg_palette);
+			drawTile((i % 32) * TILE_WIDTH, (i / 32) * TILE_HEIGHT, tile_data_address + (tile_index * TILE_SIZE));
 		}
 	}
 
@@ -135,7 +132,7 @@ void PPU::render()
 	scene.addComponent<Inferno::SpriteComponent>(m_entity, glm::vec4 { 1.0f }, texture);
 }
 
-void PPU::drawTile(uint32_t x, uint32_t y, uint32_t tile_address, uint8_t bg_palette)
+void PPU::drawTile(uint32_t x, uint32_t y, uint32_t tile_address)
 {
 	uint32_t viewport_x = Emu::the().readMemory(0xff43);
 	uint32_t viewport_y = Emu::the().readMemory(0xff42);
@@ -160,28 +157,10 @@ void PPU::drawTile(uint32_t x, uint32_t y, uint32_t tile_address, uint8_t bg_pal
 			}
 
 			uint8_t pixel_index = (pixels_lsb >> (7 - tile_x) | ((pixels_msb >> (7 - tile_x)) << 1)) & 0x3;
-			uint8_t pixel_color = (bg_palette >> (pixel_index * 2)) & 0x3;
-
-			if (pixel_color == 0) {
-				m_screen[index + 0] = 255;
-				m_screen[index + 1] = 255;
-				m_screen[index + 2] = 255;
-			}
-			else if (pixel_color == 1) {
-				m_screen[index + 0] = 168;
-				m_screen[index + 1] = 168;
-				m_screen[index + 2] = 168;
-			}
-			else if (pixel_color == 2) {
-				m_screen[index + 0] = 84;
-				m_screen[index + 1] = 84;
-				m_screen[index + 2] = 84;
-			}
-			else if (pixel_color == 3) {
-				m_screen[index + 0] = 0;
-				m_screen[index + 1] = 0;
-				m_screen[index + 2] = 0;
-			}
+			uint8_t pixel_color = getPixelColor(pixel_index, Palette::BGP);
+			m_screen[index + 0] = pixel_color;
+			m_screen[index + 1] = pixel_color;
+			m_screen[index + 2] = pixel_color;
 		}
 
 		// Move to next line
@@ -189,6 +168,36 @@ void PPU::drawTile(uint32_t x, uint32_t y, uint32_t tile_address, uint8_t bg_pal
 	}
 }
 
+uint8_t PPU::getPixelColor(uint8_t color_index, Palette palette)
+{
+	VERIFY(color_index < 4, "trying to fetch invalid color index '{}'", color_index);
+
+	switch (Emu::the().mode()) {
+	case Emu::Mode::DMG: {
+		uint8_t palette_data = Emu::the().readMemory(palette) & 0xff;
+		uint8_t palette_value = palette_data >> (color_index * 2) & 0x3;
+		switch (palette_value) {
+		case 0:
+			return 255;
+		case 1:
+			return 168;
+		case 2:
+			return 84;
+		case 3:
+			return 0;
+		default:
+			VERIFY_NOT_REACHED();
+		};
+	}
+	case Emu::Mode::CGB:
+		VERIFY_NOT_REACHED();
+	default:
+		VERIFY_NOT_REACHED();
+	}
+
+	return 0;
+}
+
 void PPU::resetFrame()
 {
 	m_state = State::OAMSearch;
diff --git a/src/ppu.h b/src/ppu.h
index 88458d3..b0043c8 100644
--- a/src/ppu.h
+++ b/src/ppu.h
@@ -8,7 +8,7 @@
 #pragma once
 
 #include <array>
-#include <cstdint> // uint8_t, uint32_t
+#include <cstdint> // uint8_t, uint16_t, uint32_t
 
 #include "ruc/meta/core.h"
 
@@ -45,10 +45,18 @@ public:
 		VBlank,
 	};
 
+	enum Palette : uint16_t {
+		BGP = 0xff47,  // BG and Window palette
+		OBP0 = 0xff48, // OBJ palette 0
+		OBP1 = 0xff49, // OBJ palette 1
+	};
+
 	void update() override;
 	void render();
 
-	void drawTile(uint32_t screen_x, uint32_t screen_y, uint32_t tile_address, uint8_t bg_palette);
+	void drawTile(uint32_t screen_x, uint32_t screen_y, uint32_t tile_address);
+	uint8_t getPixelColor(uint8_t color_index, Palette palette);
+
 	void resetFrame();
 
 private: