cocos2d-x-3.0 draw vs onDraw

Question

I'm using cocos2d-x v3.0 and in some test project I'm doing some custom drawing by overriding Node's draw method, but in the DrawPrimitives example provided they do something like this:

void DrawPrimitivesTest::draw()
{
    _customCommand.init(_globalZOrder);
    _customCommand.func = CC_CALLBACK_0(DrawPrimitivesTest::onDraw, this);
    Director::getInstance()->getRenderer()->addCommand(&_customCommand);
}

void DrawPrimitivesTest::onDraw()
{
    // drawing code here, why?
}

From reading the header and source files it seems like this may be some way of sending render commands straight to the renderer, is that correct?

Should I be using this method to do custom drawing? What's the difference between draw an onDraw?

EDIT:

As @Pedro Soares mentioned, since Cocos2D-X 3.0 you can't override draw() anymore. you have to use draw(Renderer *renderer, const kmMat4 &transform, bool transformUpdated) instead.

Answer 1

There is sample on cocos2d-x RC0 package that shows how to use the DrawPrimitives on top of other layers.

On your Layer .h add the following:

private:
    void onDrawPrimitives(const kmMat4 &transform, bool transformUpdated);
    CustomCommand _customCommand;

Now in the cpp of the Layer, override the layer draw method and include the onDrawPrimitives method:

void MyLayer::onDrawPrimitives(const kmMat4 &transform, bool transformUpdated)
{
    kmGLPushMatrix();
    kmGLLoadMatrix(&transform);

    //add your primitive drawing code here
    DrawPrimitives::drawLine(ccp(0,0), ccp(100, 100));
}

void MyLayer::draw(Renderer *renderer, const kmMat4& transform, bool transformUpdated)
{
    _customCommand.init(_globalZOrder);
    _customCommand.func = CC_CALLBACK_0(MyLayer::onDrawPrimitives, this, transform, transformUpdated);
    renderer->addCommand(&_customCommand);
}