cocos2dx源码分析：TrianglesCommand的合并渲染

cocos2dx在处理TRIANGLES_COMMAND会进行优化处理，这个优化是指合并相同材质的指令，并且共用顶点缓存和索引缓存。在无法继续合并或者达到合并上限是会调用drawBatchedTriangles一次性输出合并的TRIANGLES_COMMAND 。

    if( RenderCommand::Type::TRIANGLES_COMMAND == commandType)
    {
        // flush other queues
        flush3D();

        auto cmd = static_cast<TrianglesCommand*>(command);

        // flush own queue when buffer is full
        if(_filledVertex + cmd->getVertexCount() > VBO_SIZE || _filledIndex + cmd->getIndexCount() > INDEX_VBO_SIZE)
        {
            CCASSERT(cmd->getVertexCount()>= 0 && cmd->getVertexCount() < VBO_SIZE, "VBO for vertex is not big enough, please break the data down or use customized render command");
            CCASSERT(cmd->getIndexCount()>= 0 && cmd->getIndexCount() < INDEX_VBO_SIZE, "VBO for index is not big enough, please break the data down or use customized render command");
            /*达到合并上限会进行一次渲染输出*/
            drawBatchedTriangles();
        }
        /*进行合并处理*/
        // queue it
        _queuedTriangleCommands.push_back(cmd);
        _filledIndex += cmd->getIndexCount();
        _filledVertex += cmd->getVertexCount();
    }

共享顶点缓存和索引缓存，并且相同材质可以合并到一个渲染批次里，是否相同材质是通过一个哈希值_materialID是否相等判断的。

int glProgram = (int)_glProgram->getProgram();
int intArray[4] = { glProgram, (int)_textureID, (int)_blendType.src, (int)_blendType.dst};
_materialID = XXH32((const void*)intArray, sizeof(intArray), 0);

void Renderer::drawBatchedTriangles()
{
    /*没有渲染指令，直接退出*/
    if(_queuedTriangleCommands.empty())
        return;

    _filledVertex = 0;
    _filledIndex = 0;

    /************** 1: Setup up vertices/indices *************/
    /*数组中每个成员是一个渲染批次*/
    _triBatchesToDraw[0].offset = 0;
    _triBatchesToDraw[0].indicesToDraw = 0;
    _triBatchesToDraw[0].cmd = nullptr;

    int batchesTotal = 0;
    int prevMaterialID = -1;
    bool firstCommand = true;
    /*遍历所有渲染指令，进行合并处理*/
    for(auto it = std::begin(_queuedTriangleCommands); it != std::end(_queuedTriangleCommands); ++it)
    {
        const auto& cmd = *it;
        auto currentMaterialID = cmd->getMaterialID();
        const bool batchable = !cmd->isSkipBatching();
        /*合并顶点缓存和索引缓存*/
        fillVerticesAndIndices(cmd);

        // in the same batch ?
        if (batchable && (prevMaterialID == currentMaterialID || firstCommand))
        {
            /*合并到同一个批次进行渲染*/
            CC_ASSERT(firstCommand || _triBatchesToDraw[batchesTotal].cmd->getMaterialID() == cmd->getMaterialID() && "argh... error in logic");
            _triBatchesToDraw[batchesTotal].indicesToDraw += cmd->getIndexCount();
            _triBatchesToDraw[batchesTotal].cmd = cmd;
        }
        else
        {
            /*无法合并，增加新的批次*/
            // is this the first one?
            if (!firstCommand) {
                batchesTotal++;
                _triBatchesToDraw[batchesTotal].offset = _triBatchesToDraw[batchesTotal-1].offset + _triBatchesToDraw[batchesTotal-1].indicesToDraw;
            }

            _triBatchesToDraw[batchesTotal].cmd = cmd;
            _triBatchesToDraw[batchesTotal].indicesToDraw = (int) cmd->getIndexCount();

            // is this a single batch ? Prevent creating a batch group then
            if (!batchable)
                currentMaterialID = -1;
        }

        // capacity full ?
        if (batchesTotal + 1 >= _triBatchesToDrawCapacity) {
            _triBatchesToDrawCapacity *= 1.4;
            _triBatchesToDraw = (TriBatchToDraw*) realloc(_triBatchesToDraw, sizeof(_triBatchesToDraw[0]) * _triBatchesToDrawCapacity);
        }

        prevMaterialID = currentMaterialID;
        firstCommand = false;
    }
    batchesTotal++;

    /************** 2: Copy vertices/indices to GL objects *************/
    /*opengl es2.0不支持vao，3.0支持vao，这里根据是否支持vao分两种情况处理*/
    if (Configuration::getInstance()->supportsShareableVAO()) { /*支持vao，修改vao里顶点数据和索引数据*/ //Bind VAO GL::bindVAO(_buffersVAO); //Set VBO data glBindBuffer(GL_ARRAY_BUFFER, _buffersVBO[0]); // option 1: subdata // glBufferSubData(GL_ARRAY_BUFFER, sizeof(_quads[0])*start, sizeof(_quads[0]) * n , &_quads[start] ); // option 2: data // glBufferData(GL_ARRAY_BUFFER, sizeof(_verts[0]) * _filledVertex, _verts, GL_STATIC_DRAW); // option 3: orphaning + glMapBuffer // FIXME: in order to work as fast as possible, it must "and the exact same size and usage hints it had before." // source: https://www.opengl.org/wiki/Buffer_Object_Streaming#Explicit_multiple_buffering // so most probably we won't have any benefit of using it glBufferData(GL_ARRAY_BUFFER, sizeof(_verts[0]) * _filledVertex, nullptr, GL_STATIC_DRAW); void *buf = glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY); memcpy(buf, _verts, sizeof(_verts[0]) * _filledVertex); glUnmapBuffer(GL_ARRAY_BUFFER); glBindBuffer(GL_ARRAY_BUFFER, 0); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _buffersVBO[1]); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(_indices[0]) * _filledIndex, _indices, GL_STATIC_DRAW); } else { /*不支持vao，直接修改顶点缓存对象和索引缓存对象的数据*/ // Client Side Arrays #define kQuadSize sizeof(_verts[0]) glBindBuffer(GL_ARRAY_BUFFER, _buffersVBO[0]); glBufferData(GL_ARRAY_BUFFER, sizeof(_verts[0]) * _filledVertex , _verts, GL_DYNAMIC_DRAW); GL::enableVertexAttribs(GL::VERTEX_ATTRIB_FLAG_POS_COLOR_TEX); // vertices glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_POSITION, 3, GL_FLOAT, GL_FALSE, kQuadSize, (GLvoid*) offsetof(V3F_C4B_T2F, vertices)); // colors glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_COLOR, 4, GL_UNSIGNED_BYTE, GL_TRUE, kQuadSize, (GLvoid*) offsetof(V3F_C4B_T2F, colors)); // tex coords glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_TEX_COORD, 2, GL_FLOAT, GL_FALSE, kQuadSize, (GLvoid*) offsetof(V3F_C4B_T2F, texCoords)); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _buffersVBO[1]); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(_indices[0]) * _filledIndex, _indices, GL_STATIC_DRAW); } /*渲染输出，循环的每一次都是一个渲染批次*/ /************** 3: Draw *************/ for (int i=0; i<batchesTotal; ++i) { CC_ASSERT(_triBatchesToDraw[i].cmd && "Invalid batch"); _triBatchesToDraw[i].cmd->useMaterial();
        glDrawElements(GL_TRIANGLES, (GLsizei) _triBatchesToDraw[i].indicesToDraw, GL_UNSIGNED_SHORT, (GLvoid*) (_triBatchesToDraw[i].offset*sizeof(_indices[0])) );
        _drawnBatches++;
        _drawnVertices += _triBatchesToDraw[i].indicesToDraw;
    }
    /*渲染结束，清理数据*/
    /************** 4: Cleanup *************/
    if (Configuration::getInstance()->supportsShareableVAO()) { //Unbind VAO GL::bindVAO(0); } else { glBindBuffer(GL_ARRAY_BUFFER, 0); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0); } _queuedTriangleCommands.clear(); _filledVertex = 0; _filledIndex = 0; }