BansheeEngine/BansheeGLRenderSystem/Source/GLSL/include/BsGLSLProgramPipelineManager.h

#pragma once

#include "BsGLPrerequisites.h"

namespace BansheeEngine
{
	/**
	 * @brief	Wrapper around OpenGL pipeline object.
	 */
	struct GLSLProgramPipeline
	{
		GLuint glHandle;
	};

	/**
	 * @brief	Managed OpenGL pipeline objects that are used for binding a certain combination
	 *			of GPU programs to the render system.
	 *
	 * @note	In OpenGL you cannot bind GPU programs to the pipeline manually. Instead as a preprocessing step
	 *			you create a pipeline object containing the programs you plan on using, and then later you bind the
	 *			previously created pipeline object. 
	 */
	class GLSLProgramPipelineManager
	{
	public:
		/**
		 * @brief	Creates or returns an existing pipeline that uses the provided combination of GPU programs. Provide
		 *			null for unused programs.
		 */
		const GLSLProgramPipeline* getPipeline(GLSLGpuProgram* vertexProgram, GLSLGpuProgram* fragmentProgram, 
			GLSLGpuProgram* geometryProgram, GLSLGpuProgram* hullProgram, GLSLGpuProgram* domainProgram);

	private:
		/**
		 * @brief	Key that uniquely identifies a pipeline object.
		 */
		struct ProgramPipelineKey
		{
			UINT32 vertexProgKey;
			UINT32 fragmentProgKey;
			UINT32 geometryProgKey;
			UINT32 hullProgKey;
			UINT32 domainProgKey;
		};

		/**
		 * @brief	Used for calculating a hash code from pipeline object key.
		 */
		class ProgramPipelineKeyHashFunction 
		{
		public:
			::std::size_t operator()(const ProgramPipelineKey &key) const;
		};

		/**
		 * @brief	Used for comparing two pipeline objects for equality.
		 */
		class ProgramPipelineKeyEqual 
		{
		public:
			bool operator()(const ProgramPipelineKey &a, const ProgramPipelineKey &b) const;
		};

		typedef UnorderedMap<ProgramPipelineKey, GLSLProgramPipeline, ProgramPipelineKeyHashFunction, ProgramPipelineKeyEqual> ProgramPipelineMap;
		ProgramPipelineMap mPipelines;
	};
}