draw(renderer, viewport) {
		// empty one !
	}
Draw this renderable (automatically called by melonJS).
All draw operations for renderable are made respectively
to the position or transforms set or applied by the preDraw method.
The main draw loop will first call preDraw() to prepare the context for drawing the renderable,
then draw() to draw the renderable, and finally postDraw() to clear the context.
If you override this method, be mindful about the drawing logic; for example if you draw a shape
from the draw method, you should make sure that your draw it at the 0, 0 coordinates.
@see Renderable#preDraw
@see Renderable#postDraw
@param {CanvasRenderer|WebGLRenderer} renderer - a renderer instance
@param {Camera2d} [viewport] - the viewport to (re)draw