Handle matrix + silhouette updates better

[adroitwhiz]

Resolves

Resolves (part of) #545
Resolves #546
Resolves scratchfoundation/scratch-gui#5647

Proposed Changes

This PR makes the following changes:

• Add updateCPURenderAttributes method to Drawable
• Move CPU render attribute update from RenderWebGL._touchingBounds to RenderWebGL.isTouchingColor and RenderWebGL.isTouchingDrawables
• Add documentation notes to Drawable.isTouching, Skin.isTouchingNearest, and Skin.isTouchingLinear explaining that those functions' callers are responsible for updating the silhouette + matrix
• Update CPU render attributes in RenderWebGL._getConvexHullPointsForDrawable

Reason for Changes

• Add updateCPURenderAttributes method to Drawable

  • There were many places in RenderWebGL that called both Drawable.updateMatrix and Drawable.skin.updateSilhouette, and none that called just one or the other. Some checked whether the drawable's skin existed, others did not. I've consolidated calls to Drawable.updateMatrix and Drawable.skin.updateSilhouette into a single utility method, for conciseness and consistency.
  • This new consolidated method allows for future optimizations like this one not included in this PR, which in my testing improves "touching sprite" performance by 40-70%.
  • updateCPURenderAttributes does not multiply the drawable's scale by the screen-space scaling ratio, since CPU rendering always occurs at the "native" stage size.

• Move CPU render attribute update from RenderWebGL._touchingBounds to RenderWebGL.isTouchingColor and RenderWebGL.isTouchingDrawables

  • _touchingBounds doesn't actually require the passed drawable's matrix or silhouette to be up-to-date. However, isTouchingColor and isTouchingDrawables relied on it updating those. For clarity (and to prevent things from breaking if a future coder decided to "optimize" _touchingBounds), these calls have been moved (in the form of calls to the new updateCPURenderAttributes function) to the places that actually require the drawable's matrix and silhouette to be updated. Moved to another PR

• Add documentation notes to Drawable.isTouching, Skin.isTouchingNearest, and Skin.isTouchingLinear explaining that those functions' callers are responsible for updating the silhouette + matrix

  • This should make it clearer to future coders that they cannot use a drawable's silhouette without updating it.

• Update CPU render attributes in RenderWebGL._getConvexHullPointsForDrawable

  • This appears to be what was causing the issue in Revert "Merge pull request #394 from paulkaplan/defer-silhouette-upda… #398. _getConvexHullPointsForDrawable calls methods which require the drawable's matrix + silhouette to be up-to-date, but previously did not update them. Done in a previous PR

I have tested this manually and confirmed that it does not regress #543.

[adroitwhiz]

😳

(fortunately, this didn't break anything--all call sites specified a scale explicitly)

[cwillisf]

👍

[fsih]

LGTM, thanks!