cocos源码分析--SpriteBatchNode绘图原理

SpriteBatchNode继承Node，并实现了TextureProtocol接口，重写了Node的addChild()方法，visit()方法以及draw()方法。

addChild()方法限制其子元素只能是Sprite，

并且子元素与SpriteBatchNode必须使用同一个Texture2D对象。

visit()用于阻止元素向下遍历，将所有子元素的绘制工作交给自己处理。

draw()方法使用BatchNodeCommand将绘制命令发送到RenderQueue，从而对所有子元素进行批绘制。

SpriteBatchNode使用TextureAtlas存储所有子精灵的顶点信息。TextureAtlas包含一个V3F_C4B_T2F_Quad数组和一个Texture2D对象，提供对quads数组的添加，删除，修改，排序等功能。这样，SpriteBatchNode所做的主要事情就是将与子元素相关的顶点信息存储到TextureAtlas中。最后，TextureAtlas提供了绘制quads的方法，

BatchCommand就是通过drawQuads()方法绘制的

代码流程：

1 调用

 auto spBatchNode = SpriteBatchNode::create("bbb.png");
        spBatchNode->setPosition(Point::ZERO);
        scene->addChild(spBatchNode);
        spBatchNode->setPosition(200,200);
       // spBatchNode->setScale(0.1);

      auto sp = Sprite::createWithTexture(spBatchNode->getTexture());
           sp->setPosition(0,0);
           spBatchNode->addChild(sp,1);

          sp = Sprite::createWithTexture(spBatchNode->getTexture());
          sp->setPosition(10,10);
          spBatchNode->addChild(sp,-1);

2 看一下SpriteBatchNode内部方法

初始化方法

bool SpriteBatchNode::initWithTexture(Texture2D *tex, ssize_t capacity)
{
    CCASSERT(capacity>=0, "Capacity must be >= 0");
    
    _blendFunc = BlendFunc::ALPHA_PREMULTIPLIED;
   
    if(tex->hasPremultipliedAlpha())//alpha预乘，忽略
    {
        _blendFunc = BlendFunc::ALPHA_NON_PREMULTIPLIED;
    }
    
    //使用textureAtlas存储所有子精灵的顶点信息，通过对quads数组的添加，删除，修改排序等
    _textureAtlas = new TextureAtlas();

    if (capacity == 0)
    {
        capacity = DEFAULT_CAPACITY;
    }
    
    _textureAtlas->initWithTexture(tex, capacity);

    updateBlendFunc();

    _children.reserve(capacity);
     //分配空间大小
    _descendants.reserve(capacity);
      //定义属于自己的着色器
  setGLProgramState(GLProgramState::getOrCreateWithGLProgramName(GLProgram::SHADER_NAME_POSITION_TEXTURE_COLOR));
    return true;
}

添加子元素方法：

void SpriteBatchNode::addChild(Node * child, int zOrder, const std::string &name)
{
    CCASSERT(child != nullptr, "child should not be null");
    CCASSERT(dynamic_cast<Sprite*>(child) != nullptr, "CCSpriteBatchNode only supports Sprites as children");
    Sprite *sprite = static_cast<Sprite*>(child);
    // check Sprite is using the same texture id
    CCASSERT(sprite->getTexture()->getName() == _textureAtlas->getTexture()->getName(), "CCSprite is not using the same texture id");
    
    Node::addChild(child, zOrder, name);
    
    appendChild(sprite);
}
// addChild helper, faster than insertChild
void SpriteBatchNode::appendChild(Sprite* sprite)
{
    _reorderChildDirty=true;
    sprite->setBatchNode(this);
    sprite->setDirty(true);

    if(_textureAtlas->getTotalQuads() == _textureAtlas->getCapacity()) {
        increaseAtlasCapacity();//重新调整容器大小，
    }

    _descendants.push_back(sprite);//所有的子节点。
    int index = static_cast<int>(_descendants.size()-1);

    sprite->setAtlasIndex(index);//设置sprite的渲染节点为TextureAtlas的第index个数据

    V3F_C4B_T2F_Quad quad = sprite->getQuad();
    //把新sprite的顶点信息放到textureAtlas，供绘制使用，此时的顶点坐标还是在父亲中的坐标，不是世界坐标
    _textureAtlas->insertQuad(&quad, index);//将sprite的顶点数据传入到TextureAtlas的index位置。

    // add children recursively
    auto& children = sprite->getChildren();
    for(const auto &child: children) { //递归调用
        appendChild(static_cast<Sprite*>(child)); //将sprite的所有数据加入到descendants。
    }
}

遍历方法visit

// override visit
// don't call visit on it's children
void SpriteBatchNode::visit(Renderer *renderer, const Mat4 &parentTransform, uint32_t parentFlags)
{
    CC_PROFILER_START_CATEGORY(kProfilerCategoryBatchSprite, "CCSpriteBatchNode - visit");

    // CAREFUL:
    // This visit is almost identical to CocosNode#visit
    // with the exception that it doesn't call visit on it's children
    //
    // The alternative is to have a void Sprite#visit, but
    // although this is less maintainable, is faster
    //
    if (! _visible)
    {
        return;
    }
    //排序,写的挺不错
    sortAllChildren();
    //得到本地坐标转换世界坐标的矩阵
    uint32_t flags = processParentFlags(parentTransform, parentFlags);

    // IMPORTANT:
    // To ease the migration to v3.0, we still support the Mat4 stack,
    // but it is deprecated and your code should not rely on it
    Director* director = Director::getInstance();
    director->pushMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
    director->loadMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW, _modelViewTransform);
    
    draw(renderer, _modelViewTransform, flags);

    director->popMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
    // FIX ME: Why need to set _orderOfArrival to 0??
    // Please refer to https://github.com/cocos2d/cocos2d-x/pull/6920
//    setOrderOfArrival(0);

    CC_PROFILER_STOP_CATEGORY(kProfilerCategoryBatchSprite, "CCSpriteBatchNode - visit");
}

//override sortAllChildren
//排序功能
void SpriteBatchNode::sortAllChildren()
{
    if (_reorderChildDirty)
    {
        std::sort(std::begin(_children), std::end(_children), nodeComparisonLess);

        //sorted now check all children
        if (!_children.empty())
        {
            //first sort all children recursively based on zOrder
            for(const auto &child: _children) {
                child->sortAllChildren();
            }

            ssize_t index=0;

            //fast dispatch, give every child a new atlasIndex based on their relative zOrder (keep parent -> child relations intact)
            // and at the same time reorder descendants and the quads to the right index
            /*
             //快速发送，根据每个孩子的相对zOrder给每个孩子一个新的atlasIndex（保持父母 - >孩子的关系不变）
                    //同时重新排序descendants数组和四边形到正确的索引
             */
            //此时的childern为根据localZ从小到大排序之后的数组
            for(const auto &child: _children) {
                Sprite* sp = static_cast<Sprite*>(child);
                updateAtlasIndex(sp, &index);
            }
        }

        _reorderChildDirty=false;
    }
}
//更新sprite和sprite子节点的atlas数据的index。
void SpriteBatchNode::updateAtlasIndex(Sprite* sprite, ssize_t* curIndex)
{
    auto& array = sprite->getChildren();
    auto count = array.size();
    
    ssize_t oldIndex = 0;
    /*
       在sortAllChildren，根据localZ对children进行了排序，从小到大排序，因为之前的AtlasIndex为顺序赋值的，所以要重新设置AtlasIndex
     */
    //如果没有子节点，那么sprite就是curIndex位置了
    if( count == 0 )
    {
        oldIndex = sprite->getAtlasIndex();
        sprite->setAtlasIndex(*curIndex);//重新递增赋值
        sprite->setOrderOfArrival(0);
        
        if (oldIndex != *curIndex){
            //更新在_textureAtlas等中的位置
            swap(oldIndex, *curIndex);
        }
        (*curIndex)++;
    }
    else
    {
        bool needNewIndex=true;//是否需要赋值新的索引
        //先localZ<0的，然后sprite,最后localZ>0
        //因为先对所有的子节点排序过。先localZ<0，然后localZ>0
      
        //如果第一个localZ>=0那么先设置sprite的index
        if (array.at(0)->getLocalZOrder() >= 0)
        {
            //sprite的第一个孩子local都大于0，剩下的孩子都大于0，所以孩子绘制都在自己上面
            //all children are in front of the parent
            oldIndex = sprite->getAtlasIndex();
            sprite->setAtlasIndex(*curIndex);
            sprite->setOrderOfArrival(0);
            if (oldIndex != *curIndex)
            {
                swap(oldIndex, *curIndex);
            }
            (*curIndex)++;

            needNewIndex = false;//不需要新的索引，后面的按照顺序遍历就行
        }

        for(const auto &child: array) {
            Sprite* sp = static_cast<Sprite*>(child);
             //找到了第一个localZorder>0的，设置sprite。
            if (needNewIndex && sp->getLocalZOrder() >= 0)
            {
                oldIndex = sprite->getAtlasIndex();
                sprite->setAtlasIndex(*curIndex);
                sprite->setOrderOfArrival(0);
                if (oldIndex != *curIndex) {
                    this->swap(oldIndex, *curIndex);
                }
                (*curIndex)++;
                needNewIndex = false;
            }
            //递归调用
            updateAtlasIndex(sp, curIndex);
        }
        
        //这种情况是：所有的子节点都是localZ<0。
        //all children have a zOrder < 0)
        /*
           sprite的children已经遍历完成，最后轮到sprite自己
         */
        if (needNewIndex)
        {
            oldIndex = sprite->getAtlasIndex();
            sprite->setAtlasIndex(*curIndex);
            sprite->setOrderOfArrival(0);
            if (oldIndex != *curIndex) {
                swap(oldIndex, *curIndex);
            }
            (*curIndex)++;
        }
    }
}

swap把新排序的顶点数据更新到 quads中，用于为opengl提供基础数据

void SpriteBatchNode::swap(ssize_t oldIndex, ssize_t newIndex)
{
    CCASSERT(oldIndex>=0 && oldIndex < (int)_descendants.size() && newIndex >=0 && newIndex < (int)_descendants.size(), "Invalid index");

    V3F_C4B_T2F_Quad* quads = _textureAtlas->getQuads();
    std::swap( quads[oldIndex], quads[newIndex] );

    //update the index of other swapped item

    auto oldIt = std::next( _descendants.begin(), oldIndex );
    auto newIt = std::next( _descendants.begin(), newIndex );

    (*newIt)->setAtlasIndex(oldIndex);
//    (*oldIt)->setAtlasIndex(newIndex);

    std::swap( *oldIt, *newIt );
}

重新的元素draw方法，并不是真的绘制，而是把绘制命令放到了_batchCommand中

void SpriteBatchNode::draw(Renderer *renderer, const Mat4 &transform, uint32_t flags)
{
    // Optimization: Fast Dispatch
    if( _textureAtlas->getTotalQuads() == 0 )
    {
        return;
    }

    for(const auto &child: _children)
    {   //更新孩子的坐标，递归
        child->updateTransform();
    }

   
    _batchCommand.init(
                       _globalZOrder,
                       getGLProgram(),
                       _blendFunc,
                       _textureAtlas,
                       transform);
    renderer->addCommand(&_batchCommand);
}

void Sprite::updateTransform(void)
{
    CCASSERT(_batchNode, "updateTransform is only valid when Sprite is being rendered using an SpriteBatchNode");

    // recalculate matrix only if it is dirty
    if( isDirty() ) {

        // If it is not visible, or one of its ancestors is not visible, then do nothing:
        if( !_visible || ( _parent && _parent != _batchNode && static_cast<Sprite*>(_parent)->_shouldBeHidden) )
        {
            _quad.br.vertices = _quad.tl.vertices = _quad.tr.vertices = _quad.bl.vertices = Vec3(0,0,0);
            _shouldBeHidden = true;
        }
        else
        {
            _shouldBeHidden = false;
            //如果直接事batchNode的第一子元素，那么直接getNodeToParentTransform
            if( ! _parent || _parent == _batchNode )
            {
                 //得到子坐标转换父亲坐标的矩阵
                _transformToBatch = getNodeToParentTransform();
            }
            else //如果是batchNode的孙子或者往后，那么要下面这么做，孙子乘以transformToBatch得到在batch中的坐标
            {
                CCASSERT( dynamic_cast<Sprite*>(_parent), "Logic error in Sprite. Parent must be a Sprite");
                const Mat4 &nodeToParent = getNodeToParentTransform();
               
                Mat4 &parentTransform = static_cast<Sprite*>(_parent)->_transformToBatch;
                _transformToBatch = parentTransform * nodeToParent;
            }

            //
            // calculate the Quad based on the Affine Matrix
            //

            Size &size = _rect.size;

            float x1 = _offsetPosition.x;
            float y1 = _offsetPosition.y;

            float x2 = x1 + size.width;
            float y2 = y1 + size.height;
           
            /*
             _transformToBatch 为 本地坐标转父亲坐标的旋转矩阵。这个矩阵乘以sprite的
             [x,y,z,1],得到sprite在Batch中的的坐标
             
             */
            float x = _transformToBatch.m[12];
            float y = _transformToBatch.m[13];

            float cr = _transformToBatch.m[0];
            float sr = _transformToBatch.m[1];
            float cr2 = _transformToBatch.m[5];
            float sr2 = -_transformToBatch.m[4];
            
            float ax = x1 * cr - y1 * sr2 + x;
            float ay = x1 * sr + y1 * cr2 + y;

            float bx = x2 * cr - y1 * sr2 + x;
            float by = x2 * sr + y1 * cr2 + y;

            float cx = x2 * cr - y2 * sr2 + x;
            float cy = x2 * sr + y2 * cr2 + y;

            float dx = x1 * cr - y2 * sr2 + x;
            float dy = x1 * sr + y2 * cr2 + y;

            _quad.bl.vertices = Vec3( RENDER_IN_SUBPIXEL(ax), RENDER_IN_SUBPIXEL(ay), _positionZ );
            _quad.br.vertices = Vec3( RENDER_IN_SUBPIXEL(bx), RENDER_IN_SUBPIXEL(by), _positionZ );
            _quad.tl.vertices = Vec3( RENDER_IN_SUBPIXEL(dx), RENDER_IN_SUBPIXEL(dy), _positionZ );
            _quad.tr.vertices = Vec3( RENDER_IN_SUBPIXEL(cx), RENDER_IN_SUBPIXEL(cy), _positionZ );
        }

        // MARMALADE CHANGE: ADDED CHECK FOR nullptr, TO PERMIT SPRITES WITH NO BATCH NODE / TEXTURE ATLAS
        //把更新的四边形保存到 内存中,此时四边形的四个顶点坐标为在Batch中的坐标，不是世界坐标
        if (_textureAtlas)
        {
            _textureAtlas->updateQuad(&_quad, _atlasIndex);
        }

        _recursiveDirty = false;
        setDirty(false);
    }

    // MARMALADE CHANGED
    // recursively iterate over children
/*    if( _hasChildren )
    {
        // MARMALADE: CHANGED TO USE Node*
        // NOTE THAT WE HAVE ALSO DEFINED virtual Node::updateTransform()
        arrayMakeObjectsPerformSelector(_children, updateTransform, Sprite*);
    }*/
    //递归更新
    Node::updateTransform();
}

3 render中执行command

void Renderer::visitRenderQueue(const RenderQueue& queue)
{
    ssize_t size = queue.size();
    
    for (ssize_t index = 0; index < size; ++index)
    {
        auto command = queue[index];
        auto commandType = command->getType();
         if(RenderCommand::Type::BATCH_COMMAND == commandType)
        {
            flush();
            auto cmd = static_cast<BatchCommand*>(command);
            cmd->execute();
        }
       else
        {
            CCLOGERROR("Unknown commands in renderQueue");
        }
    }
}

4  RenderCommand 内执行execute

void BatchCommand::execute()
{
    // Set material
    _shader->use();
    
    _shader->setUniformsForBuiltins(_mv);//_mv为模型矩阵，本地坐标乘以mv，得到世界坐标
   
    glActiveTexture(GL_TEXTURE0 + 0);//0号纹理单元
    //将一个纹理对象设置为当前纹理对象，同时她会指派给当前激活了的纹理单元
    GL::bindTexture2D(_textureID);
    GL::blendFunc(_blendType.src, _blendType.dst);//颜色混合

    
    if ( _textureAtlas->getTexture()->getHasAlphaTexture()) {
        auto loc =glGetUniformLocation(_shader->getProgram(), "CC_Texture1");
        glUniform1i(loc,1);
        auto alpha=Director::getInstance()->getTextureCache()->addImage(_textureAtlas->getTexture()->getAlphaTexture());
        glActiveTexture(GL_TEXTURE0 + 1);
        glBindTexture(GL_TEXTURE_2D, alpha->getName());
    }
    
    auto locHasAlpha=glGetUniformLocation(_shader->getProgram(),"u_hasAlpha");
    glUniform1f(locHasAlpha,  _textureAtlas->getTexture()->getHasAlphaTexture()?1.0f:0.0f);
    
    // Draw，开始opengl画
    _textureAtlas->drawQuads();
}

5 textureAtlas执行drawQuads方法

void TextureAtlas::drawQuads()
{
    this->drawNumberOfQuads(_totalQuads, 0);
}

void TextureAtlas::drawNumberOfQuads(ssize_t numberOfQuads)
{
    CCASSERT(numberOfQuads>=0, "numberOfQuads must be >= 0");
    this->drawNumberOfQuads(numberOfQuads, 0);
}
//渲染start位置的numberOfQuads的数据
void TextureAtlas::drawNumberOfQuads(ssize_t numberOfQuads, ssize_t start)
{
    CCASSERT(numberOfQuads>=0 && start>=0, "numberOfQuads and start must be >= 0");

    if(!numberOfQuads)
        return;

    GL::bindTexture2D(_texture->getName());

    if (Configuration::getInstance()->supportsShareableVAO())
    {
        //
        // Using VBO and VAO
        //

        // XXX: update is done in draw... perhaps it should be done in a timer
        if (_dirty) 
        {
            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(quads_[0]) * (n-start), &quads_[start], GL_DYNAMIC_DRAW);

            // option 3: orphaning + glMapBuffer
           
            /****************************
             _quads中的顶点坐标为所有sprite在batch中的坐标，再顶点着色器中在转换为世界坐标
             ****************************/
            glBufferData(GL_ARRAY_BUFFER, sizeof(_quads[0]) * (numberOfQuads-start), nullptr, GL_DYNAMIC_DRAW);
            void *buf = glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY);
            memcpy(buf, _quads, sizeof(_quads[0])* (numberOfQuads-start));
            glUnmapBuffer(GL_ARRAY_BUFFER);
            
            glBindBuffer(GL_ARRAY_BUFFER, 0);

            _dirty = false;
        }

        GL::bindVAO(_VAOname);

#if CC_REBIND_INDICES_BUFFER
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _buffersVBO[1]);
#endif

        glDrawElements(GL_TRIANGLES, (GLsizei) numberOfQuads*6, GL_UNSIGNED_SHORT, (GLvoid*) (start*6*sizeof(_indices[0])) );

#if CC_REBIND_INDICES_BUFFER
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
#endif

//    glBindVertexArray(0);
    }
    else
    {
        //
        // Using VBO without VAO
        //

#define kQuadSize sizeof(_quads[0].bl)
        glBindBuffer(GL_ARRAY_BUFFER, _buffersVBO[0]);

        // XXX: update is done in draw... perhaps it should be done in a timer
        if (_dirty) 
        {
            glBufferSubData(GL_ARRAY_BUFFER, sizeof(_quads[0])*start, sizeof(_quads[0]) * numberOfQuads , &_quads[start] );
            _dirty = false;
        }

        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]);

        glDrawElements(GL_TRIANGLES, (GLsizei)numberOfQuads*6, GL_UNSIGNED_SHORT, (GLvoid*) (start*6*sizeof(_indices[0])));

        glBindBuffer(GL_ARRAY_BUFFER, 0);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    }

    CC_INCREMENT_GL_DRAWN_BATCHES_AND_VERTICES(1,numberOfQuads*6);

    CHECK_GL_ERROR_DEBUG();
}

以上主要步骤完成了SpriteBatchNode中sprite的绘制