1227562 - Use -moz-window-dragging on Windows instead of eMouseHitTest events

Status: RESOLVED DUPLICATE of bug 1219215

(Toolkit :: UI Widgets, defect)

Description

[Markus Stange [:mstange]]

It would be nice if we could stop sending eMouseHitTest events for testing window draggability on Windows. Windows already respects the -moz-window-dragging property, so this shouldn't be much work.

To fix this:
 - Remove the code in nsWindow.cpp that sends the eMouseHitTest event.
 - Remove the ifdefs around -moz-window-dragging CSS declarations:
https://dxr.mozilla.org/mozilla-central/search?q=%22-moz-window-dragging%3A%22&redirect=true&case=false
 - Test whether everything that was draggable before is still draggable, and whether everything that was not draggable before is still not draggable.
 - If there are differences, add the right -moz-window-dragging: drag / no-drag CSS rules to the right CSS file. (This is the tricky part.)

Comment 1

[:Felipe Gomes (needinfo for replies!)]

Another thing to test and make sure is that the dragging that happens should be the native Windows dragging (which is done by the OS and provides feedback when snapping near the edges of the screen).

There's fallback code in WindowDraggingUtils.jsm that might perform JS dragging but that's not what we want. Also, in the current setup, the code in WindowDraggingUtils.jsm is used to determine if the native dragging should happen. That part can probably be all removed if that decision is done at the widget level.