class OpenGLBackend : public ZeroedMemoryAllocator, SpriteEncoder {

private:

	static OpenGLBackend *instance; ///< Singleton instance pointer.

	GLuint vid_pbo;     ///< Pixel buffer object storing the memory used for the video driver to draw to.

	GLuint vid_texture; ///< Texture handle for the video buffer texture.

	GLuint vid_program; ///< Shader program for rendering a RGBA video buffer.

	GLuint pal_program; ///< Shader program for rendering a paletted video buffer.

	GLuint vao_quad;    ///< Vertex array object storing the rendering state for the fullscreen quad.

	GLuint vbo_quad;    ///< Vertex buffer with a fullscreen quad.

	GLuint pal_texture; ///< Palette lookup texture.

	GLuint remap_program;    ///< Shader program for blending and rendering a RGBA + remap texture.

	GLint  remap_sprite_loc; ///< Uniform location for sprite parameters.

	GLint  remap_screen_loc; ///< Uniform location for screen size;

	GLint  remap_zoom_loc;   ///< Uniform location for sprite zoom;

	GLint  remap_rgb_loc;    ///< Uniform location for RGB mode flag;

	LRUCache<SpriteID, Sprite> cursor_cache; ///< Cache of encoded cursor sprites.

	OpenGLBackend();

	~OpenGLBackend();

	const char *Init();

	}

	static const char *Create(GetOGLProcAddressProc get_proc);

	static void Destroy();

	void UpdatePalette(const Colour *pal, uint first, uint length);

	bool Resize(int w, int h, bool force = false);

	void Paint();

	void DrawMouseCursor();

	void ClearCursorCache();

	void *GetVideoBuffer();

	void ReleaseVideoBuffer(const Rect &update_rect);

	/* SpriteEncoder */

	bool Is32BppSupported() override { return true; }

	uint GetSpriteAlignment() override { return 1u << (ZOOM_LVL_COUNT - 1); }

	Sprite *Encode(const SpriteLoader::Sprite *sprite, AllocatorProc *allocator) override;

};

/** Class that encapsulates a RGBA texture together with a paletted remap texture. */

class OpenGLSprite {

private: