DrawPrimitive真是一个好类！！cocos的开发组干了好事。(一)

如果每次在商业项目中使用opengl命令去绘制特效，工作效率真心低，所以官方包装了这个接口，真实好东西。

draw函数的接口以及改了，新接口不允许重载原先的void draw(void)。

命令模式已是过去，显示列表模式则是将命令放入缓冲池中，在opengl状态机执行绘制命令时从中读取才去绘制，不再是每次绘制就调用opengl状态机立即绘制。

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这就要求引擎全局组织绘制命令，即openglcocos2d::CustomCommand

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class CustomCommand : public RenderCommand
{
public:
    CustomCommand();
    ~CustomCommand();
    
public:

    void init(float depth);

    void execute();

    inline bool isTranslucent() { return true; }
    std::function
  
    func;

protected:
};
  

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render执行单个RenderCommand时就是调用execute函数，最后访问额func成员，从而执行下面的onDraw。

最后产生一堆绘制命令。等待真正opengl去执行，实际上每条绘制函数的命令都会去flush一次。

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代码是演示效果：VisibleRect来自testCpp，或者说下面整段来自testCpp。

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void HelloWorld::draw(Renderer *renderer, const Mat4 &transform, uint32_t flags)
{
    m_customCommand.init(_globalZOrder);
    m_customCommand.func = CC_CALLBACK_0(HelloWorld::onDraw, this, transform, flags);
    renderer->addCommand(&m_customCommand);
}


void HelloWorld::onDraw(const Mat4 &transform, uint32_t flags)
{
    Director* director = Director::getInstance();
    director->pushMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
    director->loadMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW, transform);
    
    //draw
    CHECK_GL_ERROR_DEBUG();
    
    // draw a simple line
    // The default state is:
    // Line Width: 1
    // color: 255,255,255,255 (white, non-transparent)
    // Anti-Aliased
    //  glEnable(GL_LINE_SMOOTH);
    DrawPrimitives::drawLine( VisibleRect::leftBottom(), VisibleRect::rightTop() );
    
    CHECK_GL_ERROR_DEBUG();
    
    // line: color, width, aliased
    // glLineWidth > 1 and GL_LINE_SMOOTH are not compatible
    // GL_SMOOTH_LINE_WIDTH_RANGE = (1,1) on iPhone
    //  glDisable(GL_LINE_SMOOTH);
    glLineWidth( 5.0f );
    DrawPrimitives::setDrawColor4B(255,0,0,255);
    DrawPrimitives::drawLine( VisibleRect::leftTop(), VisibleRect::rightBottom() );
    
    CHECK_GL_ERROR_DEBUG();
    
    // TIP:
    // If you are going to use always thde same color or width, you don't
    // need to call it before every draw
    //
    // Remember: OpenGL is a state-machine.
    
    // draw big point in the center
    DrawPrimitives::setPointSize(64);
    DrawPrimitives::setDrawColor4B(0,0,255,128);
    DrawPrimitives::drawPoint( VisibleRect::center() );//中心的圆点，蓝色正方向
    
    CHECK_GL_ERROR_DEBUG();
    
    // draw 4 small points
    Vec2 points[] = { Vec2(60,60), Vec2(70,70), Vec2(60,70), Vec2(70,60) };
    DrawPrimitives::setPointSize(4);
    DrawPrimitives::setDrawColor4B(0,255,255,255);
    DrawPrimitives::drawPoints( points, 4);//四个青色点
    
    CHECK_GL_ERROR_DEBUG();
    
    // draw a green circle with 10 segments
    glLineWidth(16);
    DrawPrimitives::setDrawColor4B(0, 255, 0, 255);
	DrawPrimitives::drawCircle( VisibleRect::center(), 100, 2, 10, false);
    
    CHECK_GL_ERROR_DEBUG();
    
    // draw a green circle with 50 segments with line to center
    glLineWidth(2);
    DrawPrimitives::setDrawColor4B(0, 255, 255, 255);
    DrawPrimitives::drawCircle( VisibleRect::center(), 200, CC_DEGREES_TO_RADIANS(90), 50, true);
    
    CHECK_GL_ERROR_DEBUG();
    
    // draw a pink solid circle with 50 segments
    glLineWidth(2);
    DrawPrimitives::setDrawColor4B(255, 0, 255, 255);
    DrawPrimitives::drawSolidCircle( VisibleRect::center() + Vec2(140,0), 40, CC_DEGREES_TO_RADIANS(90), 50, 1.0f, 1.0f);
    
    CHECK_GL_ERROR_DEBUG();
    
    // open yellow poly
    DrawPrimitives::setDrawColor4B(255, 255, 0, 255);
    glLineWidth(10);
    Vec2 vertices[] = { Vec2(0,0), Vec2(