Cache and don't re-create transformed hull points

[adroitwhiz]

Resolves

One Two of the concerns in #365

Proposed Changes

• Create Rectangles per-Drawable for holding get(Fast)Bounds results
• Store transformed convex hull points in an array initialized when un-transformed convex hull points are initialized
• Add "transformed convex hull dirty" flag

Reason for Changes

• Create Rectangles per-Drawable for holding get(Fast)Bounds results

Drawable.getBounds, Drawable.getBoundsForBubble, Drawable.getFastBounds, and Drawable.getAABB take an optional result parameter (a Rectangle). If given, it will be set to the drawable's bounds.

If a result parameter was not passed, however, those functions would create an entirely new Rectangle on each call. To make things worse, they're called from several places in the codebase without a result being passed.

Now, each Drawable instantiates its own Rectangles to hold the bounds results only once: when the Drawable itself is created. This should prevent unnecessary creation of Rectangles.

• Store transformed convex hull points in an array initialized when un-transformed convex hull points are initialized

Previously, calling _getTransformedHullPoints would result in an entirely new array being created and filled up with twgl.v3 objects each time.

Now, the array is created and filled with twgl.v3 objects only when the convex hull itself changes. _getTransformedHullPoints now modifies these twgl.v3 objects in-place. This change should greatly reduce the number of unnecessary objects created.

• Add "transformed convex hull dirty" flag

Previously, calling _getTransformedHullPoints meant always recalculating the positions of transformed convex hull points. Now, they are only recalculated when the transform has actually changed.

These changes greatly reduce the allocations made by convex-hull functions:

"Vector scaling performance test 2" (makes heavy use of "if on edge, bounce")

Before	After

[cwillisf]

Have you verified that callers never modify the contents of the array returned by this function?

[adroitwhiz]

_getTransformedHullPoints is called by getBounds and getBoundsForBubble.

getBounds passes it to Rectangle.initFromPointsAABB which does not modify the array.

getBoundsForBubble calls map and filter on the array, both of which create new arrays instead of modifying in-place.

[cwillisf]

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