VertexBuffer.cpp

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/* Copyright (C) 2013 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/>.
 */

/*
 * encapsulation of VBOs with sharing
 */

#include "precompiled.h"
#include "ps/Errors.h"
#include "lib/ogl.h"
#include "lib/sysdep/cpu.h"
#include "Renderer.h"
#include "VertexBuffer.h"
#include "VertexBufferManager.h"
#include "ps/CLogger.h"

CVertexBuffer::CVertexBuffer(size_t vertexSize, GLenum usage, GLenum target)
    : m_VertexSize(vertexSize), m_Handle(0), m_SysMem(0), m_Usage(usage), m_Target(target)
{
    size_t size = MAX_VB_SIZE_BYTES;

    if (target == GL_ARRAY_BUFFER) // vertex data buffer
    {
        // We want to store 16-bit indices to any vertex in a buffer, so the
        // buffer must never be bigger than vertexSize*64K bytes since we can 
        // address at most 64K of them with 16-bit indices
        size = std::min(size, vertexSize*65536);
    }

    // allocate raw buffer
    if (g_Renderer.m_Caps.m_VBO)
    {
        pglGenBuffersARB(1, &m_Handle);
        pglBindBufferARB(m_Target, m_Handle);
        pglBufferDataARB(m_Target, size, 0, m_Usage);
        pglBindBufferARB(m_Target, 0);
    }
    else
    {
        m_SysMem = new u8[size];
    }

    // store max/free vertex counts
    m_MaxVertices = m_FreeVertices = size/vertexSize;
    
    // create sole free chunk
    VBChunk* chunk = new VBChunk;
    chunk->m_Owner = this;
    chunk->m_Count = m_FreeVertices;
    chunk->m_Index = 0;
    m_FreeList.push_front(chunk);
}

CVertexBuffer::~CVertexBuffer()
{
    if (m_Handle)
        pglDeleteBuffersARB(1, &m_Handle);

    delete[] m_SysMem;

    typedef std::list<VBChunk*>::iterator Iter;
    for (Iter iter = m_FreeList.begin(); iter != m_FreeList.end(); ++iter)
        delete *iter;
}


bool CVertexBuffer::CompatibleVertexType(size_t vertexSize, GLenum usage, GLenum target)
{
    if (usage != m_Usage || target != m_Target || vertexSize != m_VertexSize)
        return false;

    return true;
}

///////////////////////////////////////////////////////////////////////////////
// Allocate: try to allocate a buffer of given number of vertices (each of 
// given size), with the given type, and using the given texture - return null 
// if no free chunks available
CVertexBuffer::VBChunk* CVertexBuffer::Allocate(size_t vertexSize, size_t numVertices, GLenum usage, GLenum target)
{
    // check this is the right kind of buffer
    if (!CompatibleVertexType(vertexSize, usage, target))
        return 0;

    // quick check there's enough vertices spare to allocate
    if (numVertices > m_FreeVertices)
        return 0;

    // trawl free list looking for first free chunk with enough space
    VBChunk* chunk = 0;
    typedef std::list<VBChunk*>::iterator Iter;
    for (Iter iter = m_FreeList.begin(); iter != m_FreeList.end(); ++iter) {
        if (numVertices <= (*iter)->m_Count) {
            chunk = *iter;
            // remove this chunk from the free list
            m_FreeList.erase(iter);
            m_FreeVertices -= chunk->m_Count;
            // no need to search further ..
            break;
        }
    }

    if (!chunk) {
        // no big enough spare chunk available
        return 0;
    }

    // split chunk into two; - allocate a new chunk using all unused vertices in the 
    // found chunk, and add it to the free list
    if (chunk->m_Count > numVertices)
    {
        VBChunk* newchunk = new VBChunk;
        newchunk->m_Owner = this;
        newchunk->m_Count = chunk->m_Count - numVertices;
        newchunk->m_Index = chunk->m_Index + numVertices;
        m_FreeList.push_front(newchunk);
        m_FreeVertices += newchunk->m_Count;

        // resize given chunk
        chunk->m_Count = numVertices;
    }
    
    // return found chunk
    return chunk;
}

///////////////////////////////////////////////////////////////////////////////
// Release: return given chunk to this buffer
void CVertexBuffer::Release(VBChunk* chunk)
{
    // Update total free count before potentially modifying this chunk's count
    m_FreeVertices += chunk->m_Count;

    typedef std::list<VBChunk*>::iterator Iter;

    // Coalesce with any free-list items that are adjacent to this chunk;
    // merge the found chunk with the new one, and remove the old one
    // from the list, and repeat until no more are found
    bool coalesced;
    do
    {
        coalesced = false;
        for (Iter iter = m_FreeList.begin(); iter != m_FreeList.end(); ++iter)
        {
            if ((*iter)->m_Index == chunk->m_Index + chunk->m_Count
             || (*iter)->m_Index + (*iter)->m_Count == chunk->m_Index)
            {
                chunk->m_Index = std::min(chunk->m_Index, (*iter)->m_Index);
                chunk->m_Count += (*iter)->m_Count;
                delete *iter;
                m_FreeList.erase(iter);
                coalesced = true;
                break;
            }
        }
    }
    while (coalesced);

    m_FreeList.push_front(chunk);
}

///////////////////////////////////////////////////////////////////////////////
// UpdateChunkVertices: update vertex data for given chunk
void CVertexBuffer::UpdateChunkVertices(VBChunk* chunk, void* data)
{
    if (g_Renderer.m_Caps.m_VBO)
    {
        ENSURE(m_Handle);
        pglBindBufferARB(m_Target, m_Handle);
        pglBufferSubDataARB(m_Target, chunk->m_Index * m_VertexSize, chunk->m_Count * m_VertexSize, data);
        pglBindBufferARB(m_Target, 0);
    }
    else
    {
        ENSURE(m_SysMem);
        memcpy(m_SysMem + chunk->m_Index * m_VertexSize, data, chunk->m_Count * m_VertexSize);
    }
}

///////////////////////////////////////////////////////////////////////////////
// Bind: bind to this buffer; return pointer to address required as parameter
// to glVertexPointer ( + etc) calls
u8* CVertexBuffer::Bind()
{
    if (g_Renderer.m_Caps.m_VBO)
    {
        pglBindBufferARB(m_Target, m_Handle);
        return (u8*)0;
    }
    else
    {
        return m_SysMem;
    }
}

u8* CVertexBuffer::GetBindAddress()
{
    if (g_Renderer.m_Caps.m_VBO)
        return (u8*)0;
    else
        return m_SysMem;
}

void CVertexBuffer::Unbind()
{
    if (g_Renderer.m_Caps.m_VBO)
    {
        pglBindBufferARB(GL_ARRAY_BUFFER, 0);
        pglBindBufferARB(GL_ELEMENT_ARRAY_BUFFER, 0);
    }
}

size_t CVertexBuffer::GetBytesReserved() const
{
    return MAX_VB_SIZE_BYTES;
}

size_t CVertexBuffer::GetBytesAllocated() const
{
    return (m_MaxVertices - m_FreeVertices) * m_VertexSize;
}

void CVertexBuffer::DumpStatus()
{
    debug_printf(L"freeverts = %d\n", (int)m_FreeVertices);

    size_t maxSize = 0;
    typedef std::list<VBChunk*>::iterator Iter;
    for (Iter iter = m_FreeList.begin(); iter != m_FreeList.end(); ++iter)
    {
        debug_printf(L"free chunk %p: size=%d\n", *iter, (int)((*iter)->m_Count));
        maxSize = std::max((*iter)->m_Count, maxSize);
    }
    debug_printf(L"max size = %d\n", (int)maxSize);
}