Should pointer event bubble up when only a tap is enabled? about taach

[axelpale]

It is possible that the temptation of making every item touchable is the most robust way. Tapping items when multiple users are interacting with the space could otherwise become problematic. Also, finding the topmost item given a coordinate in space is not a trivial task, but it would be needed if only the container captured everything.

[axelpale]

A simple approach is to provide a new mode property: propagate. This boolean, when true, would disable ev.stopPropagation() calls, causing the events to bubble up. The programmer could then control when to bubble. Changing the propagation behaviour would be as simple as updating the mode.

On the other hand, the approach opens a possibility for a non-trivial error. If a node and its ancestor can both be transformed, bubbling the events would cause the node to be double transformed.

Another approach would be to always propagate when the mode enables only tap. This probably leads to even more weird bugs because the behaviour is hidden inside taach. Also, tapping with a little pinch could activate the native pinch zoom, and that is not something to expect.

Therefore it seems that the propagate property is our best choice. It is probably simple to implement, only adds to current API, and is explicit for the programmer.