[css-async-style] CompositorWorker use cases

[ianvollick]

To complement the list of scrolling use cases that's been started, it would be nice to build a list of non-scrolling effects that might be enabled via something like CompositorWorker.

Here are some examples to get the ball rolling:

• Simple side-drawers which can be dragged out from the side, sticking to the finger
• Simple custom panning that sticks to the finger and can fling in arbitrary directions (eg. google maps)
• Drag-and-drop interfaces where elements “skootch” out of the way to make room for the dragged element (or other animations to illustrate potential drop targets).
• Animating force-directed, springy/physical application layout. For example, drawers with inertia/friction or even more exotic, physics-based interfaces like BumpTop.
• Animating constraint based application layout transitions (eg, responding to the addition of new views to a Cassowary layout).
• Applications where the compositor thread is the control thread.
• If access to input is available, input filtering.

[flackr]

In addition to custom panning and drag and drop that sticks to the finger there are also pinch and rotate cases:

• Simple custom panning, pinching, rotation that sticks to the finger and can fling in arbitrary direction (e.g. google maps on mobile supports all of these).
• Sticky custom panning, pinching, rotation: e.g. in addition to the above, stick slightly at 0 degree rotation to prevent accidental rotation when zooming.
• Drag and drop and resize and rotate. E.g. a publisher like application where you can not only reposition items but resize and rotate them.