video_core: Rewrite to backend system

* Still doesn't build this is just a massive code dump from all the recent progress

src/video_core/common/framebuffer.h

@@ -0,0 +1,69 @@
+// Copyright 2022 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include "video_core/common/texture.h"
+
+namespace VideoCore {
+
+enum class MSAASamples : u32 {
+    x1,
+    x2,
+    x4,
+    x8
+};
+
+/**
+ * Information about a framebuffer
+ */
+struct FramebufferInfo {
+    TextureHandle color;
+    TextureHandle depth_stencil;
+    MSAASamples samples = MSAASamples::x1;
+    Rect2D draw_rect{};
+
+    /// Hashes the framebuffer object and returns a unique identifier
+    const u64 Hash() const {
+        // The only member IntrusivePtr has is a pointer to the
+        // handle so it's fine hash it
+        return Common::ComputeStructHash64(*this);
+    }
+};
+
+/**
+ * A framebuffer is a collection of render targets and their configuration
+ */
+class FramebufferBase : public IntrusivePtrEnabled<FramebufferBase> {
+public:
+    FramebufferBase(const FramebufferInfo& info) : info(info) {}
+    virtual ~FramebufferBase() = default;
+
+    /// Returns an immutable reference to the color attachment
+    const TextureHandle& GetColorAttachment() const {
+        return info.color;
+    }
+
+    /// Returns an immutable reference to the depth/stencil attachment
+    const TextureHandle& GetDepthStencilAttachment() const {
+        return info.depth_stencil;
+    }
+
+    /// Returns how many samples the framebuffer takes
+    MSAASamples GetMSAASamples() const {
+        return info.samples;
+    }
+
+    /// Returns the rendering area
+    Rect2D GetDrawRectangle() const {
+        return info.draw_rect;
+    }
+
+protected:
+    FramebufferInfo info;
+};
+
+using FramebufferHandle = IntrusivePtr<FramebufferBase>;
+
+} // namespace VideoCore