VAOCache.h

/*     Copyright 2015-2018 Egor Yusov
 *  
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF ANY PROPRIETARY RIGHTS.
 *
 *  In no event and under no legal theory, whether in tort (including negligence), 
 *  contract, or otherwise, unless required by applicable law (such as deliberate 
 *  and grossly negligent acts) or agreed to in writing, shall any Contributor be
 *  liable for any damages, including any direct, indirect, special, incidental, 
 *  or consequential damages of any character arising as a result of this License or 
 *  out of the use or inability to use the software (including but not limited to damages 
 *  for loss of goodwill, work stoppage, computer failure or malfunction, or any and 
 *  all other commercial damages or losses), even if such Contributor has been advised 
 *  of the possibility of such damages.
 */

#pragma once

#include <cstring>
#include "GraphicsTypes.h"
#include "Buffer.h"
#include "InputLayout.h"
#include "LockHelper.h"
#include "HashUtils.h"
#include "DeviceContextBase.h"
#include "BaseInterfacesGL.h"

namespace Diligent
{

class VAOCache
{
public:
    VAOCache();
    ~VAOCache();

    VAOCache(const VAOCache&)  = delete;
    VAOCache(      VAOCache&&) = delete;
    VAOCache& operator = (const VAOCache&)  = delete;
    VAOCache& operator = (      VAOCache&&) = delete;
    
    

    const GLObjectWrappers::GLVertexArrayObj& GetVAO( IPipelineState *pPSO,
                                                      IBuffer *pIndexBuffer,
                                                      VertexStreamInfo VertexStreams[],
                                                      Uint32 NumVertexStreams,
                                                      class GLContextState &GLContextState);
    const GLObjectWrappers::GLVertexArrayObj& GetEmptyVAO();

    void OnDestroyBuffer(IBuffer *pBuffer);
    void OnDestroyPSO(IPipelineState *pPSO);

private:
    // This structure is used as the key to find VAO
    struct VAOCacheKey
    {
        VAOCacheKey(const IPipelineState* pso, const IBuffer* indBuffer) : 
            pPSO(pso),
            pIndexBuffer(indBuffer),
            NumUsedSlots(0)
        {}

        // Note that the the pointers are used for ordering only
        // They are not used to access the objects

        // VAO encapsulates both input layout and all bound buffers
        // PSO uniqly defines the layout (attrib pointers, divisors, etc.),
        // so we do not need to add individual layout elements to the key
        // The keey needs to contain all bound buffers
        const IPipelineState* const pPSO;
        const IBuffer* const pIndexBuffer;
        Uint32 NumUsedSlots;
        struct StreamAttribs
        {
            const IBuffer* pBuffer;
            Uint32 Stride;
            Uint32 Offset;
        }Streams[MaxBufferSlots];
        
        mutable size_t Hash = 0;

        bool operator == (const VAOCacheKey &Key)const
        {
            return pPSO            == Key.pPSO            &&
                   pIndexBuffer    == Key.pIndexBuffer    &&
                   NumUsedSlots    == Key.NumUsedSlots    &&
                   std::memcmp(Streams, Key.Streams, sizeof(StreamAttribs) * NumUsedSlots) == 0;
        }
    };

    struct VAOCacheKeyHashFunc
    {
        std::size_t operator() ( const VAOCacheKey& Key )const
        {
            if (Key.Hash == 0)
            {
                std::size_t Seed = 0;
                HashCombine(Seed, Key.pPSO, Key.NumUsedSlots);
                if (Key.pIndexBuffer)
                    HashCombine(Seed, Key.pIndexBuffer);
                for (Uint32 slot = 0; slot < Key.NumUsedSlots; ++slot)
                {
                    auto &CurrStream = Key.Streams[slot];
                    if (CurrStream.pBuffer)
                    {
                        HashCombine(Seed, CurrStream.pBuffer);
                        HashCombine(Seed, CurrStream.Offset);
                        HashCombine(Seed, CurrStream.Stride);
                    }
                }
                Key.Hash = Seed;
            }
            return Key.Hash;
        }
    };


    friend class RenderDeviceGLImpl;
    ThreadingTools::LockFlag m_CacheLockFlag;
    std::unordered_map<VAOCacheKey, GLObjectWrappers::GLVertexArrayObj, VAOCacheKeyHashFunc> m_Cache;
    std::unordered_multimap<const IPipelineState*, VAOCacheKey> m_PSOToKey;
    std::unordered_multimap<const IBuffer*, VAOCacheKey> m_BuffToKey;

    // Any draw command fails if no VAO is bound. We will use this empty
    // VAO for draw commands with null input layout, such as these that
    // only use VertexID as input.
    GLObjectWrappers::GLVertexArrayObj m_EmptyVAO;
};

}