Starling handbook Preview

Pivot Points
The code also introduces the concept of pivot points. Per default, the root of an
image is at the top left (just as the stage’s root is at the top left). Via the pivotX and
pivotY properties, you can move that root (the pivot point) to a different location.
Above, we are moving the pivot point to the center of the bird’s body, which has
two advantages:
1. Should we want to rotate the bird later, it will rotate around its center.
2. It will simplify the collision detection code we need to write a little later.
Run the project now to see the bird airborne!
Figure 7. The bird is in the air.
Something seems to be wrong, though: there is no flapping animation, just a static image!
That’s because the MovieClip doesn’t have any information about the passage of time yet; and
without that information, it will simply stick to the very first frame.
In this case, we want to have full control over the bird’s animation, so we update it manually once
per frame. Let’s do this by adding the following method to the World class:
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