https://github.com/w3c/pointerevents/issues/194 A user agent must fire a pointer event pointercancel immediately before drag operation starts.

(In reply to Ming-Chou Shih [:stone] from comment #0) > https://github.com/w3c/pointerevents/issues/194 > > A user agent must fire a pointer event pointercancel immediately before drag > operation starts. We should fire pointercancel, implicitly release pointer capture, and stop firing subsequent pointer events when starting a dnd session.

(In reply to Ming-Chou Shih [:stone] from comment #1) > (In reply to Ming-Chou Shih [:stone] from comment #0) > > https://github.com/w3c/pointerevents/issues/194 > > > > A user agent must fire a pointer event pointercancel immediately before drag > > operation starts. > > We should fire pointercancel, implicitly release pointer capture, and stop > firing subsequent pointer events when starting a dnd session. Spec doesn't clearly describe when to continue firing pointer events. Fired https://github.com/w3c/pointerevents/issues/222 to discuss it.

We should have this for shipping Pointer events, so setting P1

Spec [1] defines that input events must be suppressed when starting a dnd operation until it is finished. Now we fire mousemove / pointermove because they are queued in the content process when starting a dnd operation, which is separated to bug 1414204. This bug only covers the behaviour to fire pointercancel when starting a dnd operation. [1] http://w3c.github.io/html/editing.html#drag-and-drop-processing-model

Comment on attachment 8925040 [details] [diff] [review] Fire pointercancel when starting a dnd operation. > if (status != nsEventStatus_eConsumeNoDefault) { > bool dragStarted = DoDefaultDragStart(aPresContext, event, dataTransfer, > targetContent, selection); > if (dragStarted) { > sActiveESM = nullptr; >+ MaybeFirePointerCancel(aEvent); > aEvent->StopPropagation(); > } > } Aha, this was a tad surprising but I see the event is dispatched only if dragstart wasn't cancelled.

Pushed by sshih@mozilla.com: https://hg.mozilla.org/integration/mozilla-inbound/rev/f763151e6c59 Fire pointercancel when starting a dnd operation. r=smaug.