opengl: restructure code for computing format support.

src/modules/graphics/opengl/Graphics.h

@@ -155,6 +155,8 @@ private:
 
 	void setDebug(bool enable);
 
+	uint32 computePixelFormatUsage(PixelFormat format, bool readable);
+
 	std::unordered_map<RenderTargets, GLuint, CachedFBOHasher> framebufferObjects;
 	bool windowHasStencil;
 	GLuint mainVAO;
@@ -170,8 +172,8 @@ private:
 	// Only needed for buffer types that can be bound to shaders.
 	StrongRef<love::graphics::Buffer> defaultBuffers[BUFFERUSAGE_MAX_ENUM];
 
-	// [rendertarget][readable][computewrite][srgb]
-	OptionalBool supportedFormats[PIXELFORMAT_MAX_ENUM][2][2][2][2];
+	// [non-readable, readable]
+	uint32 pixelFormatUsage[PIXELFORMAT_MAX_ENUM][2];
 
 }; // Graphics