GteConstantBuffer.h

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// David Eberly, Geometric Tools, Redmond WA 98052
// Copyright (c) 1998-2017
// Distributed under the Boost Software License, Version 1.0.
// http://www.boost.org/LICENSE_1_0.txt
// http://www.geometrictools.com/License/Boost/LICENSE_1_0.txt
// File Version: 3.0.1 (2016/08/29)

#pragma once

#include <LowLevel/GteLogger.h>
#include <Graphics/GteBuffer.h>
#include <Graphics/GteMemberLayout.h>
#include <algorithm>

namespace gte
{

class GTE_IMPEXP ConstantBuffer : public Buffer
{
public:
    // Construction.
    ConstantBuffer(size_t numBytes, bool allowDynamicUpdate);

    // Access to constant buffer members using the layout of a shader
    // program itself is allowed as long as you have attached the constant
    // buffer to a shader first.
    //   std::shared_ptr<VertexShader> vshader = <some shader>;
    //   std::shared_ptr<ConstantBuffer> cbuffer = <buffer for the shader>;
    //   vshader->Set("MyCBuffer", cbuffer);
    // Now you can use SetMember/GetMember calls successfully.  In these
    // calls, you are required to specify the correct type T for the member.
    // No checking is performed for the size of the input; i.e., too large a
    // 'value' will cause a memory overwrite within the buffer.  The code
    // does test to ensure that no overwrite occurs outside the buffer.

    inline void SetLayout(std::vector<MemberLayout> const& layout);
    inline std::vector<MemberLayout> const& GetLayout() const;

    // Test for existence of a member with the specified name.
    bool HasMember(std::string const& name) const;

    // Set or get a non-array member.
    template <typename T>
    bool SetMember(std::string const& name, T const& value);

    template <typename T>
    bool GetMember(std::string const& name, T& value) const;

    // Set or get an array member.
    template <typename T>
    bool SetMember(std::string const& name, unsigned int index,
        T const& value);

    template <typename T>
    bool GetMember(std::string const& name, unsigned int index,
        T& value) const;

protected:
    // Direct3D 11 requires the storage to be a multiple of 16 bytes.
    // Direct3D 12 requires the storage to be a multiple of 256 bytes.
    // This function rounds to the nearest multiple when allocating
    // buffer memory.
    static size_t GetRoundedNumBytes(size_t numBytes);

    std::vector<MemberLayout> mLayout;

public:
    // For use by the Shader class for storing reflection information.
    static int const shaderDataLookup = 0;
};


inline void ConstantBuffer::SetLayout(std::vector<MemberLayout> const& layout)
{
    mLayout = layout;
}

inline std::vector<MemberLayout> const& ConstantBuffer::GetLayout() const
{
    return mLayout;
}

template <typename T>
bool ConstantBuffer::SetMember(std::string const& name, T const& value)
{
    auto iter = std::find_if(mLayout.begin(), mLayout.end(),
        [&name](MemberLayout const& item){ return name == item.name; });

    if (iter == mLayout.end())
    {
        LogError("Failed to find member name " + name + ".");
        return false;
    }

    if (iter->numElements > 0)
    {
        LogError("Member is an array, use SetMember(name,index,value).");
        return false;
    }

    if (iter->offset + sizeof(T) > mNumBytes)
    {
        LogError("Writing will access memory outside the buffer.");
        return false;
    }

    T* target = reinterpret_cast<T*>(mData + iter->offset);
    *target = value;
    return true;
}

template <typename T>
bool ConstantBuffer::GetMember(std::string const& name, T& value) const
{
    auto iter = std::find_if(mLayout.begin(), mLayout.end(),
        [&name](MemberLayout const& item){ return name == item.name; });

    if (iter == mLayout.end())
    {
        LogError("Failed to find member name " + name + ".");
        return false;
    }

    if (iter->numElements > 0)
    {
        LogError("Member is an array, use GetMember(name,index,value).");
        return false;
    }

    if (iter->offset + sizeof(T) > mNumBytes)
    {
        LogError("Reading will access memory outside the buffer.");
        return false;
    }

    T* target = reinterpret_cast<T*>(mData + iter->offset);
    value = *target;
    return true;
}

template <typename T>
bool ConstantBuffer::SetMember(std::string const& name, unsigned int index,
    T const& value)
{
    auto iter = std::find_if(mLayout.begin(), mLayout.end(),
        [&name](MemberLayout const& item){ return name == item.name; });

    if (iter == mLayout.end())
    {
        LogError("Failed to find member name " + name + ".");
        return false;
    }

    if (iter->numElements == 0)
    {
        LogError("Member is a singleton, use SetMember(name,value).");
        return false;
    }

    if (index >= iter->numElements)
    {
        LogError("Index is out of range for the member array.");
        return false;
    }

    if (iter->offset + (index + 1)*sizeof(T) > mNumBytes)
    {
        LogError("Writing will access memory outside the buffer.");
        return false;
    }

    T* target = reinterpret_cast<T*>(mData + iter->offset + index*sizeof(T));
    *target = value;
    return true;
}

template <typename T>
bool ConstantBuffer::GetMember(std::string const& name, unsigned int index,
    T& value) const
{
    auto iter = std::find_if(mLayout.begin(), mLayout.end(),
        [&name](MemberLayout const& item){ return name == item.name; });

    if (iter == mLayout.end())
    {
        LogError("Failed to find member name " + name + ".");
        return false;
    }

    if (iter->numElements == 0)
    {
        LogError("Member is a singleton, use GetMember(name,value).");
        return false;
    }

    if (index >= iter->numElements)
    {
        LogError("Index is out of range for the member array.");
        return false;
    }

    if (iter->offset + (index + 1)*sizeof(T) > mNumBytes)
    {
        LogError("Reading will access memory outside the buffer.");
        return false;
    }

    T* target = reinterpret_cast<T*>(mData + iter->offset + index*sizeof(T));
    value = *target;
    return true;
}


}