Clean up the 3D renderer for enhanced flexibility (#1895)

* Give `GPU2D::Unit` a virtual destructor

- Undefined behavior avoided!

* Add an `array2d` alias

* Move various parts of `GPU2D::SoftRenderer` to `constexpr`

- `SoftRenderer::MosaicTable` is now initialized at compile-time
- Most of the `SoftRenderer::Color*` functions are now `constexpr`
- The aforementioned functions are used with a constant value in at least one place, so they'll be at least partially computed at compile-time

* Generalize `GLRenderer::PrepareCaptureFrame`

- Declare it in the base `Renderer3D` class, but make it empty

* Remove unneeded `virtual` specifiers

* Store `Framebuffer`'s memory in `unique_ptr`s

- Reduce the risk of leaks this way

* Clean up how `GLCompositor` is initialized

- Return it as an `std::optional` instead of a `std::unique_ptr`
- Make `GLCompositor` movable
- Replace `GLCompositor`'s plain arrays with `std::array` to simplify moving

* Pass `GPU` to `GLCompositor`'s important functions instead of passing it to the constructor

* Move `GLCompositor` to be a field within `GLRenderer`

- Some methods were moved up and made `virtual`

* Fix some linker errors

* Set the renderer in the frontend

* Remove unneeded `virtual` specifiers

* Remove `RenderSettings` in favor of just exposing the relevant member variables

* Update the frontend to accommodate the core changes

* Add `constexpr` and `const` to places in the interpolator

* Qualify references to `size_t`

* Construct the `optional` directly instead of using `make_optional`

- It makes the Linux build choke
- I think it's because `GLCompositor`'s constructor is `private`

src/GPU_OpenGL.h

@@ -21,51 +21,51 @@
 #include "OpenGLSupport.h"
 
 #include <array>
-#include <memory>
+#include <optional>
 
 namespace melonDS
 {
 class GPU;
 struct RenderSettings;
-
+class GLRenderer;
 class GLCompositor
 {
 public:
-    static std::unique_ptr<GLCompositor> New(melonDS::GPU& gpu) noexcept;
+    static std::optional<GLCompositor> New() noexcept;
     GLCompositor(const GLCompositor&) = delete;
     GLCompositor& operator=(const GLCompositor&) = delete;
+    GLCompositor(GLCompositor&&) noexcept;
+    GLCompositor& operator=(GLCompositor&&) noexcept;
     ~GLCompositor();
 
-    void Reset();
+    void SetScaleFactor(int scale) noexcept;
+    [[nodiscard]] int GetScaleFactor() const noexcept { return Scale; }
 
-    void SetRenderSettings(const RenderSettings& settings) noexcept;
-
-    void Stop();
-    void RenderFrame();
+    void Stop(const GPU& gpu) noexcept;
+    void RenderFrame(const GPU& gpu, GLRenderer& renderer) noexcept;
     void BindOutputTexture(int buf);
 private:
-    GLCompositor(std::array<GLuint, 3> CompShader, melonDS::GPU& gpu) noexcept;
-    melonDS::GPU& GPU;
-    int Scale;
-    int ScreenH, ScreenW;
+    GLCompositor(std::array<GLuint, 3> CompShader) noexcept;
+    int Scale = 0;
+    int ScreenH = 0, ScreenW = 0;
 
-    std::array<GLuint, 3> CompShader;
-    GLuint CompScaleLoc;
-    GLuint Comp3DXPosLoc;
+    std::array<GLuint, 3> CompShader {};
+    GLuint CompScaleLoc = 0;
+    GLuint Comp3DXPosLoc = 0;
 
-    GLuint CompVertexBufferID;
-    GLuint CompVertexArrayID;
+    GLuint CompVertexBufferID = 0;
+    GLuint CompVertexArrayID = 0;
 
     struct CompVertex
     {
-        float Position[2];
-        float Texcoord[2];
+        std::array<float, 2> Position {};
+        std::array<float, 2> Texcoord {};
     };
-    CompVertex CompVertices[2 * 3*2];
+    std::array<CompVertex, 2*3*2> CompVertices {};
 
-    GLuint CompScreenInputTex;
-    GLuint CompScreenOutputTex[2];
-    GLuint CompScreenOutputFB[2];
+    GLuint CompScreenInputTex = 0;
+    std::array<GLuint, 2> CompScreenOutputTex {};
+    std::array<GLuint, 2> CompScreenOutputFB {};
 };
 
 }