Introduce "Renderer" abstraction layer

Adds a `renderer` class for which a rendering backend must implement and
will conditionally use OpenGL in the case that `ENABLE_GL` is enabled.

include/renderer.hpp

@@ -0,0 +1,37 @@
+#pragma once
+#include <array>
+#include <span>
+
+#include "PICA/pica_vertex.hpp"
+#include "PICA/regs.hpp"
+#include "helpers.hpp"
+
+class GPU;
+
+class Renderer {
+  protected:
+	GPU& gpu;
+	static constexpr u32 regNum = 0x300;  // Number of internal PICA registers
+	const std::array<u32, regNum>& regs;
+
+  public:
+	Renderer(GPU& gpu, const std::array<u32, regNum>& internalRegs);
+	virtual ~Renderer();
+
+	static constexpr u32 vertexBufferSize = 0x10000;
+
+	virtual void reset() = 0;
+	virtual void display() = 0;                                                              // Display the 3DS screen contents to the window
+	virtual void initGraphicsContext() = 0;                                                  // Initialize graphics context
+	virtual void clearBuffer(u32 startAddress, u32 endAddress, u32 value, u32 control) = 0;  // Clear a GPU buffer in VRAM
+	virtual void displayTransfer(u32 inputAddr, u32 outputAddr, u32 inputSize, u32 outputSize, u32 flags) = 0;  // Perform display transfer
+	virtual void drawVertices(PICA::PrimType primType, std::span<const PICA::Vertex> vertices) = 0;             // Draw the given vertices
+
+	virtual void setFBSize(u32 width, u32 height) = 0;
+
+	virtual void setColourFormat(PICA::ColorFmt format) = 0;
+	virtual void setDepthFormat(PICA::DepthFmt format) = 0;
+
+	virtual void setColourBufferLoc(u32 loc) = 0;
+	virtual void setDepthBufferLoc(u32 loc) = 0;
+};