VertexArray.h

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/* Copyright (C) 2012 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef INCLUDED_VERTEXARRAY
#define INCLUDED_VERTEXARRAY

#include "renderer/VertexBuffer.h"

// Iterator
template<typename T>
class VertexArrayIterator
{
public:
    typedef T Type;

public:
    VertexArrayIterator() :
        m_Data(0), m_Stride(0)
    {
    }
    
    VertexArrayIterator(char* data, size_t stride) :
        m_Data(data), m_Stride(stride)
    {
    }

    VertexArrayIterator(const VertexArrayIterator& rhs) :
        m_Data(rhs.m_Data), m_Stride(rhs.m_Stride)
    {
    }

    VertexArrayIterator& operator=(const VertexArrayIterator& rhs)
    {
        m_Data = rhs.m_Data;
        m_Stride = rhs.m_Stride;
        return *this;
    }

    // Accessors
    T& operator*() const { return *(T*)m_Data; }
    T* operator->() const { return (T*)m_Data; }
    T& operator[](size_t idx) const { return *(T*)(m_Data + idx*m_Stride); }

    // Walking
    VertexArrayIterator& operator++()
    {
        m_Data += m_Stride;
        return *this;
    }
    VertexArrayIterator operator++(int)
    {
        VertexArrayIterator tmp = *this;
        m_Data += m_Stride;
        return tmp;
    }
    VertexArrayIterator& operator--()
    {
        m_Data -= m_Stride;
        return *this;
    }
    VertexArrayIterator operator--(int)
    {
        VertexArrayIterator tmp = *this;
        m_Data -= m_Stride;
        return tmp;
    }

    VertexArrayIterator& operator+=(ssize_t rhs)
    {
        m_Data += rhs*m_Stride;
        return *this;
    }
    VertexArrayIterator& operator-=(ssize_t rhs)
    {
        m_Data -= rhs*m_Stride;
        return *this;
    }

    VertexArrayIterator operator+(ssize_t rhs) const
    {
        VertexArrayIterator tmp = *this;
        tmp.m_Data += rhs*m_Stride;
        return tmp;
    }
    VertexArrayIterator operator-(ssize_t rhs) const
    {
        VertexArrayIterator tmp = *this;
        tmp.m_Data -= rhs*m_Stride;
        return tmp;
    }

    // Accessors for raw buffer data, for performance-critical code
    char* GetData() const
    {
        return m_Data;
    }
    size_t GetStride() const
    {
        return m_Stride;
    }

private:
    char* m_Data;
    size_t m_Stride;
};


// Manage a vertex array with a runtime-determined set of attributes.
//
// Purpose: Different rendering paths sometimes require different sets of
// attributes (e.g. normal vector vs. color data), which is difficult to
// support with hardcoded vertex structures.
// This class chooses the vertex layout at runtime, based on the attributes
// that are actually needed.
//
// Note that this class will not allocate any OpenGL resources until one
// of the Upload functions is called.
class VertexArray
{
public:
    struct Attribute
    {
        // Data type. Currently supported: GL_FLOAT, GL_SHORT, GL_UNSIGNED_SHORT, GL_UNSIGNED_BYTE.
        GLenum type;
        // How many elements per vertex (e.g. 3 for RGB, 2 for UV)
        GLuint elems;
        
        // Offset (in bytes) into a vertex structure (filled in by Layout())
        size_t offset;
        
        VertexArray* vertexArray;

        Attribute() : type(0), elems(0), offset(0), vertexArray(0) { }
    
        // Get an iterator over the backing store for the given attribute that 
        // initially points at the first vertex.
        // Supported types T: CVector3D, CVector4D, float[2], SColor3ub, SColor4ub,
        // u16, u16[2], u8, u8[4], short, short[2].
        // This function verifies at runtime that the requested type T matches
        // the attribute definition passed to AddAttribute().
        template<typename T>
        VertexArrayIterator<T> GetIterator() const;
    };
    
public:
    VertexArray(GLenum usage, GLenum target = GL_ARRAY_BUFFER);
    ~VertexArray();
    
    // Set the number of vertices stored in the array
    void SetNumVertices(size_t num);
    // Add vertex attributes
    void AddAttribute(Attribute* attr);

    size_t GetNumVertices() const { return m_NumVertices; }
    size_t GetStride() const { return m_Stride; }
    
    // Layout the vertex array format and create backing buffer in RAM.
    // You must call Layout() after changing the number of vertices or
    // attributes.
    // All vertex data is lost when a vertex array is re-layouted.
    void Layout();
    // (Re-)Upload the attributes of the vertex array from the backing store to
    // the underlying VBO object.
    void Upload();
    // Bind this array, returns the base address for calls to glVertexPointer etc.
    u8* Bind();

    // If you know for certain that you'll never have to change the data again,
    // call this to free some memory.
    void FreeBackingStore();
    
private:
    void Free();

    template<typename T>
    VertexArrayIterator<T> MakeIterator(const Attribute* attr)
    {
        ENSURE(attr->type && attr->elems);
        return VertexArrayIterator<T>(m_BackingStore + attr->offset, m_Stride);
    }

    GLenum m_Usage;
    GLenum m_Target;
    size_t m_NumVertices;
    std::vector<Attribute*> m_Attributes;

    CVertexBuffer::VBChunk* m_VB;
    size_t m_Stride;
    char* m_BackingStore; // 16-byte aligned, to allow fast SSE access
};

/**
 * A VertexArray that is specialised to handle 16-bit array indices.
 * Call Bind() and pass the return value to the indices parameter of
 * glDrawElements/glDrawRangeElements/glMultiDrawElements.
 * Use CVertexBuffer::Unbind() to unbind the array when done.
 */
class VertexIndexArray : public VertexArray
{
public:
    VertexIndexArray(GLenum usage);

    /// Gets the iterator over the (only) attribute in this array, i.e. a u16.
    VertexArrayIterator<u16> GetIterator() const;

private:
    Attribute m_Attr;
};

#endif // INCLUDED_VERTEXARRAY