/* -*-c++-*- OpenSceneGraph - Copyright (C) 1998-2006 Robert Osfield 
 *
 * This library is open source and may be redistributed and/or modified under  
 * the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or 
 * (at your option) any later version.  The full license is in LICENSE file
 * included with this distribution, and on the openscenegraph.org website.
 * 
 * This library 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 
 * OpenSceneGraph Public License for more details.
*/
#include <stdio.h>
#include <math.h>
#include <float.h>

#include <osg/BufferObject>
#include <osg/Notify>
#include <osg/GLExtensions>
#include <osg/Timer>
#include <osg/Image>
#include <osg/State>
#include <osg/PrimitiveSet>
#include <osg/Array>

#include <OpenThreads/ScopedLock>
#include <OpenThreads/Mutex>

using namespace osg;

// static cache of deleted display lists which can only 
// by completely deleted once the appropriate OpenGL context
// is set.  Used osg::BufferObject::deleteDisplayList(..) and flushDeletedBufferObjects(..) below.
typedef std::multimap<unsigned int,GLuint> DisplayListMap;
typedef osg::buffered_object<DisplayListMap> DeletedBufferObjectCache;

static OpenThreads::Mutex s_mutex_deletedBufferObjectCache;
static DeletedBufferObjectCache s_deletedBufferObjectCache;

void BufferObject::deleteBufferObject(unsigned int contextID,GLuint globj)
{
    if (globj!=0)
    {
        OpenThreads::ScopedLock<OpenThreads::Mutex> lock(s_mutex_deletedBufferObjectCache);
        
        // insert the globj into the cache for the appropriate context.
        s_deletedBufferObjectCache[contextID].insert(DisplayListMap::value_type(0,globj));
    }
}

/** flush all the cached display list which need to be deleted
  * in the OpenGL context related to contextID.*/
void BufferObject::flushDeletedBufferObjects(unsigned int contextID,double /*currentTime*/, double& availableTime)
{
    // if no time available don't try to flush objects.
    if (availableTime<=0.0) return;

    const osg::Timer& timer = *osg::Timer::instance();
    osg::Timer_t start_tick = timer.tick();
    double elapsedTime = 0.0;


    {
        OpenThreads::ScopedLock<OpenThreads::Mutex> lock(s_mutex_deletedBufferObjectCache);

        const Extensions* extensions = getExtensions(contextID,true);

        unsigned int noDeleted = 0;

        DisplayListMap& dll = s_deletedBufferObjectCache[contextID];

        DisplayListMap::iterator ditr=dll.begin();
        for(;
            ditr!=dll.end() && elapsedTime<availableTime;
            ++ditr)
        {
            extensions->glDeleteBuffers(1,&(ditr->second));
            elapsedTime = timer.delta_s(start_tick,timer.tick());
            ++noDeleted;
        }
        if (ditr!=dll.begin()) dll.erase(dll.begin(),ditr);

        if (noDeleted!=0) notify(osg::INFO)<<"Number VBOs deleted = "<<noDeleted<<std::endl;
    }    
    
    availableTime -= elapsedTime;
}


BufferObject::BufferObject():
    _target(0),
    _usage(0),
    _totalSize(0)
{
}

BufferObject::BufferObject(const BufferObject& bo,const CopyOp& copyop):
    Object(bo,copyop)
{
}

BufferObject::~BufferObject()
{
    releaseGLObjects(0);
}

void BufferObject::resizeGLObjectBuffers(unsigned int maxSize)
{
    _bufferObjectList.resize(maxSize);
}

void BufferObject::releaseGLObjects(State* state) const
{
    if (state)
    {
        unsigned int contextID = state->getContextID();
        if (_bufferObjectList[contextID])
        {
             deleteBufferObject(contextID,_bufferObjectList[contextID]);
            _bufferObjectList[contextID] = 0;
        }
    }
    else
    {
        for(unsigned int contextID=0;contextID<_bufferObjectList.size();++contextID)
        {
            if (_bufferObjectList[contextID])
            {
                 deleteBufferObject(contextID,_bufferObjectList[contextID]);
                _bufferObjectList[contextID] = 0;
            }
        }
    }
}

//////////////////////////////////////////////////////////////////////////////
//
//  Extension support
//

typedef buffered_value< ref_ptr<BufferObject::Extensions> > BufferedExtensions;
static BufferedExtensions s_extensions;

BufferObject::Extensions* BufferObject::getExtensions(unsigned int contextID,bool createIfNotInitalized)
{
    if (!s_extensions[contextID] && createIfNotInitalized) s_extensions[contextID] = new BufferObject::Extensions(contextID);
    return s_extensions[contextID].get();
}

void BufferObject::setExtensions(unsigned int contextID,Extensions* extensions)
{
    s_extensions[contextID] = extensions;
}

BufferObject::Extensions::Extensions(unsigned int contextID)
{
    setupGLExtensions(contextID);
}

BufferObject::Extensions::Extensions(const Extensions& rhs):
    Referenced()
{
    _glGenBuffers = rhs._glGenBuffers;
    _glBindBuffer = rhs._glBindBuffer;
    _glBufferData = rhs._glBufferData;
    _glBufferSubData = rhs._glBufferSubData;
    _glDeleteBuffers = rhs._glDeleteBuffers;
    _glIsBuffer = rhs._glIsBuffer;
    _glGetBufferSubData = rhs._glGetBufferSubData;
    _glMapBuffer = rhs._glMapBuffer;
    _glUnmapBuffer = rhs._glUnmapBuffer;
    _glGetBufferParameteriv = rhs._glGetBufferParameteriv;
    _glGetBufferPointerv = rhs._glGetBufferPointerv;
}


void BufferObject::Extensions::lowestCommonDenominator(const Extensions& rhs)
{
    if (!rhs._glGenBuffers) _glGenBuffers = rhs._glGenBuffers;
    if (!rhs._glBindBuffer) _glBindBuffer = rhs._glBindBuffer;
    if (!rhs._glBufferData) _glBufferData = rhs._glBufferData;
    if (!rhs._glBufferSubData) _glBufferSubData = rhs._glBufferSubData;
    if (!rhs._glDeleteBuffers) _glDeleteBuffers = rhs._glDeleteBuffers;
    if (!rhs._glIsBuffer) _glIsBuffer = rhs._glIsBuffer;
    if (!rhs._glGetBufferSubData) _glGetBufferSubData = rhs._glGetBufferSubData;
    if (!rhs._glMapBuffer) _glMapBuffer = rhs._glMapBuffer;
    if (!rhs._glUnmapBuffer) _glUnmapBuffer = rhs._glUnmapBuffer;
    if (!rhs._glGetBufferParameteriv) _glGetBufferParameteriv = rhs._glGetBufferParameteriv;
    if (!rhs._glGetBufferParameteriv) _glGetBufferPointerv = rhs._glGetBufferPointerv;
}

void BufferObject::Extensions::setupGLExtensions(unsigned int contextID)
{
    _glGenBuffers = ((GenBuffersProc)osg::getGLExtensionFuncPtr("glGenBuffers","glGenBuffersARB"));
    _glBindBuffer = ((BindBufferProc)osg::getGLExtensionFuncPtr("glBindBuffer","glBindBufferARB"));
    _glBufferData = ((BufferDataProc)osg::getGLExtensionFuncPtr("glBufferData","glBufferDataARB"));
    _glBufferSubData = ((BufferSubDataProc)osg::getGLExtensionFuncPtr("glBufferSubData","glBufferSubDataARB"));
    _glDeleteBuffers = ((DeleteBuffersProc)osg::getGLExtensionFuncPtr("glDeleteBuffers","glDeleteBuffersARB"));
    _glIsBuffer = ((IsBufferProc)osg::getGLExtensionFuncPtr("glIsBuffer","glIsBufferARB"));
    _glGetBufferSubData = ((GetBufferSubDataProc)osg::getGLExtensionFuncPtr("glGetBufferSubData","glGetBufferSubDataARB"));
    _glMapBuffer = ((MapBufferProc)osg::getGLExtensionFuncPtr("glMapBuffer","glMapBufferARB"));
    _glUnmapBuffer = ((UnmapBufferProc)osg::getGLExtensionFuncPtr("glUnmapBuffer","glUnmapBufferARB"));
    _glGetBufferParameteriv = ((GetBufferParameterivProc)osg::getGLExtensionFuncPtr("glGetBufferParameteriv","glGetBufferParameterivARB"));
    _glGetBufferPointerv = ((GetBufferPointervProc)osg::getGLExtensionFuncPtr("glGetBufferPointerv","glGetBufferPointervARB"));
    _isPBOSupported = osg::isGLExtensionSupported(contextID,"GL_ARB_pixel_buffer_object");
}

void BufferObject::Extensions::glGenBuffers(GLsizei n, GLuint *buffers) const
{
    if (_glGenBuffers) _glGenBuffers(n, buffers); 
    else notify(WARN)<<"Error: glGenBuffers not supported by OpenGL driver"<<std::endl;
}

void BufferObject::Extensions::glBindBuffer(GLenum target, GLuint buffer) const
{
    if (_glBindBuffer) _glBindBuffer(target, buffer); 
    else notify(WARN)<<"Error: glBindBuffer not supported by OpenGL driver"<<std::endl;
}

void BufferObject::Extensions::glBufferData(GLenum target, GLsizeiptrARB size, const GLvoid *data, GLenum usage) const
{
    if (_glBufferData) _glBufferData(target, size, data, usage); 
    else notify(WARN)<<"Error: glBufferData not supported by OpenGL driver"<<std::endl;
}

void BufferObject::Extensions::glBufferSubData(GLenum target, GLintptrARB offset, GLsizeiptrARB size, const GLvoid *data) const
{
    if (_glBufferSubData) _glBufferSubData(target, offset, size, data); 
    else notify(WARN)<<"Error: glBufferData not supported by OpenGL driver"<<std::endl;
}

void BufferObject::Extensions::glDeleteBuffers(GLsizei n, const GLuint *buffers) const
{
    if (_glDeleteBuffers) _glDeleteBuffers(n, buffers); 
    else notify(WARN)<<"Error: glBufferData not supported by OpenGL driver"<<std::endl;
}

GLboolean BufferObject::Extensions::glIsBuffer (GLuint buffer) const
{
    if (_glIsBuffer) return _glIsBuffer(buffer);
    else 
    {
        notify(WARN)<<"Error: glIsBuffer not supported by OpenGL driver"<<std::endl;
        return GL_FALSE;
    }
}

void BufferObject::Extensions::glGetBufferSubData (GLenum target, GLintptrARB offset, GLsizeiptrARB size, GLvoid *data) const
{
    if (_glGetBufferSubData) _glGetBufferSubData(target,offset,size,data);
    else notify(WARN)<<"Error: glGetBufferSubData not supported by OpenGL driver"<<std::endl;
}

GLvoid* BufferObject::Extensions::glMapBuffer (GLenum target, GLenum access) const
{
    if (_glMapBuffer) return _glMapBuffer(target,access);
    else 
    {
        notify(WARN)<<"Error: glMapBuffer not supported by OpenGL driver"<<std::endl;
        return 0;
    }
}

GLboolean BufferObject::Extensions::glUnmapBuffer (GLenum target) const
{
    if (_glUnmapBuffer) return _glUnmapBuffer(target);
    else 
    {
        notify(WARN)<<"Error: glUnmapBuffer not supported by OpenGL driver"<<std::endl;
        return GL_FALSE;
    }
}

void BufferObject::Extensions::glGetBufferParameteriv (GLenum target, GLenum pname, GLint *params) const
{
    if (_glGetBufferParameteriv) _glGetBufferParameteriv(target,pname,params);
    else notify(WARN)<<"Error: glGetBufferParameteriv not supported by OpenGL driver"<<std::endl;
}

void BufferObject::Extensions::glGetBufferPointerv (GLenum target, GLenum pname, GLvoid* *params) const
{
    if (_glGetBufferPointerv) _glGetBufferPointerv(target,pname,params);
    else notify(WARN)<<"Error: glGetBufferPointerv not supported by OpenGL driver"<<std::endl;
}

//////////////////////////////////////////////////////////////////////////////////
//
//  VertexBufferObject
//
VertexBufferObject::VertexBufferObject()
{
    _target = GL_ARRAY_BUFFER_ARB;
    _usage = GL_STATIC_DRAW_ARB;
//    _usage = GL_DYNAMIC_DRAW_ARB;
//    _usage = GL_STREAM_DRAW_ARB;
}

VertexBufferObject::VertexBufferObject(const VertexBufferObject& vbo,const CopyOp& copyop):
    BufferObject(vbo,copyop)
{
}

VertexBufferObject::~VertexBufferObject()
{
}

unsigned int VertexBufferObject::addArray(osg::Array* array)
{
    unsigned int i = _bufferEntryArrayPairs.size();

    _bufferEntryArrayPairs.resize(i+1);
    _bufferEntryArrayPairs[i].second = array;
    _bufferEntryArrayPairs[i].first.modifiedCount.setAllElementsTo(0xffffffff);
    _bufferEntryArrayPairs[i].first.offset = 0;
    
    dirty();
    
    return i;
}

void VertexBufferObject::removeArray(osg::Array* array)
{
    BufferEntryArrayPairs::iterator itr;
    for(itr = _bufferEntryArrayPairs.begin();
        itr != _bufferEntryArrayPairs.end();
        ++itr)
    {
        if (itr->second == array) break;
    }
    if (itr != _bufferEntryArrayPairs.end()) _bufferEntryArrayPairs.erase(itr);
}

void VertexBufferObject::setArray(unsigned int i, Array* array)
{
    if (i+1>=_bufferEntryArrayPairs.size()) _bufferEntryArrayPairs.resize(i+1); 
    
    _bufferEntryArrayPairs[i].second = array;
    _bufferEntryArrayPairs[i].first.modifiedCount.setAllElementsTo(0xffffffff);
    _bufferEntryArrayPairs[i].first.offset = 0;

    dirty();
} 
void VertexBufferObject::compileBuffer(State& state) const
{
    unsigned int contextID = state.getContextID();

    _compiledList[contextID] = 1;
    
    Extensions* extensions = getExtensions(contextID,true);

    // osg::notify(osg::NOTICE)<<"VertexBufferObject::compileBuffer frameNumber="<<state.getFrameStamp()->getFrameNumber()<<std::endl;

    unsigned int totalSizeRequired = 0;
    unsigned int numModified = 0;
    unsigned int numNotModified = 0;
    for(BufferEntryArrayPairs::const_iterator itr = _bufferEntryArrayPairs.begin();
        itr != _bufferEntryArrayPairs.end();
        ++itr)
    {
        const BufferEntryArrayPair& bep = *itr;
        if (bep.second)
        {
            totalSizeRequired += bep.second->getTotalDataSize();
        }
    }

    bool copyAll = false;
    GLuint& vbo = buffer(contextID);
    if (vbo==0)
    {
        // building for the first time.

        _totalSize = totalSizeRequired;

        // don't generate buffer if size is zero.        
        if (_totalSize==0) return;

        extensions->glGenBuffers(1, &vbo);
        extensions->glBindBuffer(_target, vbo);
        extensions->glBufferData(_target, _totalSize, NULL, _usage);
        
        copyAll = true;           
    }
    else
    {
        extensions->glBindBuffer(_target, vbo);

        if (_totalSize != totalSizeRequired)
        {
            // resize vbo.
            _totalSize = totalSizeRequired;
            extensions->glBufferData(_target, _totalSize, NULL, _usage);
            
            copyAll = true;           
        }
    }

//    osg::Timer_t start_tick = osg::Timer::instance()->tick();


    void* vboMemory = 0; 

#if 0
    vboMemory = extensions->glMapBuffer(_target, GL_WRITE_ONLY_ARB);
#endif

    unsigned int offset = 0;
    for(BufferEntryArrayPairs::const_iterator itr = _bufferEntryArrayPairs.begin();
        itr != _bufferEntryArrayPairs.end();
        ++itr)
    {
        const BufferEntryArrayPair& bep = *itr;
        const Array* de = bep.second;
        if (de)
        {
            if (copyAll || 
                bep.first.modifiedCount[contextID] != bep.second->getModifiedCount() ||
                bep.first.dataSize != bep.second->getTotalDataSize())
            {
                // copy data across
                bep.first.dataSize = bep.second->getTotalDataSize();
                bep.first.modifiedCount[contextID] = de->getModifiedCount();
                if (copyAll) 
                {
                    bep.first.offset = offset;
                    de->setVertexBufferObjectOffset((GLvoid*)offset);
                    offset += bep.first.dataSize;
                }
                
                // osg::notify(osg::NOTICE)<<"   copying vertex buffer data "<<bep.first.dataSize<<" bytes"<<std::endl;
                
                if (vboMemory)
                    memcpy((char*)vboMemory + bep.first.offset, de->getDataPointer(), bep.first.dataSize);
                else
                    extensions->glBufferSubData(_target, bep.first.offset, bep.first.dataSize, de->getDataPointer());

            }
        }
    }

        
    // Unmap the texture image buffer
    if (vboMemory) extensions->glUnmapBuffer(_target);
    
//    osg::notify(osg::NOTICE)<<"pbo _totalSize="<<_totalSize<<std::endl;
//    osg::notify(osg::NOTICE)<<"pbo "<<osg::Timer::instance()->delta_m(start_tick,osg::Timer::instance()->tick())<<"ms"<<std::endl;
}

void VertexBufferObject::resizeGLObjectBuffers(unsigned int maxSize)
{
    BufferObject::resizeGLObjectBuffers(maxSize);
    
    for(BufferEntryArrayPairs::iterator itr = _bufferEntryArrayPairs.begin();
        itr != _bufferEntryArrayPairs.end();
        ++itr)
    {
        itr->first.modifiedCount.resize(maxSize);
    }
}

//////////////////////////////////////////////////////////////////////////////////
//
//  ElementBufferObject
//
ElementBufferObject::ElementBufferObject()
{
    _target = GL_ELEMENT_ARRAY_BUFFER_ARB;
    _usage = GL_STATIC_DRAW_ARB;
}

ElementBufferObject::ElementBufferObject(const ElementBufferObject& vbo,const CopyOp& copyop):
    BufferObject(vbo,copyop)
{
}

ElementBufferObject::~ElementBufferObject()
{
}

unsigned int ElementBufferObject::addDrawElements(osg::DrawElements* drawElements)
{
    unsigned int i = _bufferEntryDrawElementsPairs.size();
    _bufferEntryDrawElementsPairs.resize(i+1);
    _bufferEntryDrawElementsPairs[i].second = drawElements;
    _bufferEntryDrawElementsPairs[i].first.modifiedCount.setAllElementsTo(0xffffffff);
    _bufferEntryDrawElementsPairs[i].first.dataSize = 0;
 
    return i;
}

void ElementBufferObject::removeDrawElements(osg::DrawElements* drawElements)
{
    BufferEntryDrawElementsPairs::iterator itr;
    for(itr = _bufferEntryDrawElementsPairs.begin();
        itr != _bufferEntryDrawElementsPairs.end();
        ++itr)
    {
        if (itr->second == drawElements) break;
    }
    if (itr != _bufferEntryDrawElementsPairs.end()) _bufferEntryDrawElementsPairs.erase(itr);
}

void ElementBufferObject::setDrawElements(unsigned int i, DrawElements* drawElements)
{
    if (i+1>=_bufferEntryDrawElementsPairs.size()) _bufferEntryDrawElementsPairs.resize(i+1); 
    
    _bufferEntryDrawElementsPairs[i].second = drawElements;
    _bufferEntryDrawElementsPairs[i].first.modifiedCount.setAllElementsTo(0xffffffff);
    _bufferEntryDrawElementsPairs[i].first.dataSize = 0;
}

void ElementBufferObject::compileBuffer(State& state) const
{
    unsigned int contextID = state.getContextID();

    _compiledList[contextID] = 1;

    // osg::notify(osg::NOTICE)<<"ElementBufferObject::compile"<<std::endl;
    
    Extensions* extensions = getExtensions(contextID,true);

    unsigned int totalSizeRequired = 0;
    unsigned int numModified = 0;
    unsigned int numNotModified = 0;
    for(BufferEntryDrawElementsPairs::const_iterator itr = _bufferEntryDrawElementsPairs.begin();
        itr != _bufferEntryDrawElementsPairs.end();
        ++itr)
    {
        const BufferEntryDrawElementsPair& bep = *itr;
        if (bep.second)
        {
            totalSizeRequired += bep.second->getTotalDataSize();
        }
    }

    bool copyAll = false;
    GLuint& ebo = buffer(contextID);
    if (ebo==0)
    {
        // building for the first time.

        _totalSize = totalSizeRequired;

        // don't generate buffer if size is zero.        
        if (_totalSize==0) return;

        extensions->glGenBuffers(1, &ebo);
        extensions->glBindBuffer(_target, ebo);
        extensions->glBufferData(_target, _totalSize, NULL, _usage);
        
        copyAll = true;           
    }
    else
    {
        extensions->glBindBuffer(_target, ebo);

        if (_totalSize != totalSizeRequired)
        {
            // resize EBO.
            _totalSize = totalSizeRequired;
            extensions->glBufferData(_target, _totalSize, NULL, _usage);
            
            copyAll = true;           
        }
    }

//    osg::Timer_t start_tick = osg::Timer::instance()->tick();


    void* eboMemory = 0; 

#if 0
    eboMemory = extensions->glMapBuffer(_target, GL_WRITE_ONLY_ARB);
#endif

    unsigned int offset = 0;
    for(BufferEntryDrawElementsPairs::const_iterator itr = _bufferEntryDrawElementsPairs.begin();
        itr != _bufferEntryDrawElementsPairs.end();
        ++itr)
    {
        const BufferEntryDrawElementsPair& bep = *itr;
        const DrawElements* de = bep.second;
        if (de)
        {
            if (copyAll || 
                bep.first.modifiedCount[contextID] != bep.second->getModifiedCount() ||
                bep.first.dataSize != bep.second->getTotalDataSize())
            {
                // copy data across
                bep.first.dataSize = bep.second->getTotalDataSize();
                bep.first.modifiedCount[contextID] = de->getModifiedCount();
                if (copyAll) 
                {
                    bep.first.offset = offset;
                    de->setElementBufferObjectOffset((GLvoid*)offset);
                    offset += bep.first.dataSize;
                }
                
                if (eboMemory)
                    memcpy((char*)eboMemory + bep.first.offset, de->getDataPointer(), bep.first.dataSize);
                else
                    extensions->glBufferSubData(_target, bep.first.offset, bep.first.dataSize, de->getDataPointer());

            }
        }
    }

        
    // Unmap the texture image buffer
    if (eboMemory) extensions->glUnmapBuffer(_target);

//    osg::notify(osg::NOTICE)<<"pbo _totalSize="<<_totalSize<<std::endl;
//    osg::notify(osg::NOTICE)<<"pbo "<<osg::Timer::instance()->delta_m(start_tick,osg::Timer::instance()->tick())<<"ms"<<std::endl;
}

void ElementBufferObject::resizeGLObjectBuffers(unsigned int maxSize)
{
    BufferObject::resizeGLObjectBuffers(maxSize);
    
    for(BufferEntryDrawElementsPairs::iterator itr = _bufferEntryDrawElementsPairs.begin();
        itr != _bufferEntryDrawElementsPairs.end();
        ++itr)
    {
        itr->first.modifiedCount.resize(maxSize);
    }
}

//////////////////////////////////////////////////////////////////////////////////
//
//  PixelBufferObject
//
PixelBufferObject::PixelBufferObject(osg::Image* image):
    BufferObject()
{
    _target = GL_PIXEL_UNPACK_BUFFER_ARB;
    _usage = GL_STREAM_DRAW_ARB;
    _bufferEntryImagePair.second = image;
}

/** Copy constructor using CopyOp to manage deep vs shallow copy.*/
PixelBufferObject::PixelBufferObject(const PixelBufferObject& buffer,const CopyOp& copyop):
    BufferObject(buffer,copyop),
    _bufferEntryImagePair(buffer._bufferEntryImagePair)
{
}

PixelBufferObject::~PixelBufferObject()
{
}

void PixelBufferObject::setImage(osg::Image* image)
{
    if (_bufferEntryImagePair.second == image) return;
    
    _bufferEntryImagePair.second = image;
    
    dirty();
}
void PixelBufferObject::compileBuffer(State& state) const
{
    unsigned int contextID = state.getContextID();
    
    _compiledList[contextID] = 1;

    osg::Image* image = _bufferEntryImagePair.second;

    _bufferEntryImagePair.first.modifiedCount[contextID] = image->getModifiedCount();
    if (!image->valid()) return;

    Extensions* extensions = getExtensions(contextID,true);

    GLuint& pbo = buffer(contextID);
    if (pbo==0)
    {
        // building for the first time.

        _totalSize = image->getTotalSizeInBytes();

        // don't generate buffer if size is zero.        
        if (_totalSize==0) return;

        extensions->glGenBuffers(1, &pbo);
        extensions->glBindBuffer(_target, pbo);
        extensions->glBufferData(_target, _totalSize, NULL, _usage);
                    
    }
    else
    {
        extensions->glBindBuffer(_target, pbo);

        if (_totalSize != image->getTotalSizeInBytes())
        {
            // resize PBO.
            _totalSize = image->getTotalSizeInBytes();
            extensions->glBufferData(_target, _totalSize, NULL, _usage);
        }
    }

//    osg::Timer_t start_tick = osg::Timer::instance()->tick();

    void* pboMemory = extensions->glMapBuffer(_target,
                 GL_WRITE_ONLY_ARB);

    // copy data across
    memcpy(pboMemory, image->data(), _totalSize);
        
    // Unmap the texture image buffer
    extensions->glUnmapBuffer(_target);

    _bufferEntryImagePair.first.modifiedCount[contextID] = image->getModifiedCount();

//    osg::notify(osg::NOTICE)<<"pbo _totalSize="<<_totalSize<<std::endl;
//    osg::notify(osg::NOTICE)<<"pbo "<<osg::Timer::instance()->delta_m(start_tick,osg::Timer::instance()->tick())<<"ms"<<std::endl;
}

void PixelBufferObject::resizeGLObjectBuffers(unsigned int maxSize)
{
    BufferObject::resizeGLObjectBuffers(maxSize);
    
    _bufferEntryImagePair.first.modifiedCount.resize(maxSize);
}