bug#28620: Interact directly on Emacs bug#28620: mouse drag event records wrong release window

[Robert Weiner]

On Tue, Oct 3, 2017 at 6:40 PM, Alan Third <alan@idiocy.org> wrote:

On Tue, Oct 03, 2017 at 02:21:43PM -0400, Robert Weiner wrote:
> This happens consistently in testing.  This must be a bug in mouse-position
> for macOS, right?  Why would (mouse-position) still report f1 when f2 is
> the selected frame?  Maybe this is why I am seeing the wrong frame on drag
> releases too.

As far as I can tell ns_mouse_position returns the frame stored in
dpyinfo->last_mouse_frame, which is set by EmacsView::mouseDown, however:

    If the user clicks a view that isn’t in the key window, by default
    the window is brought forward and made key, but the mouse event is
    not dispatched.

​What does "the mouse event is not dispatched mean"?  Does it mean Emacs never sees the event?  Maybe Emacs sees only that the window has been selected by the window manager and based on that switches to the selected window of the frame?

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        https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/EventOverview/HandlingMouseEvents/HandlingMouseEvents.html

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My guess is that ns_mouse_position needs to get a list of NSWindows,

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iterate over them to find out which one the mouse pointer is over,

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convert that NSWindow back to an Emacs frame, and set *fp to it before

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returning.

​The mouse wheel code manages to scroll the proper window that the mouse is over, even across overlapping frames where the window the mouse is over is in a frame that is partially behind another frame.  And this happens without without any click events.  This could be utilized in the click event code to get this right somehow.

It looks like the EV_TRAILER macro call at the end of the nsterm.c mouseDown function (which is also called by mouseUp) sets the frame used for mouse button down, up and scroll wheel events from the variable emacsframe.  Somehow the value of emacsframe must be set differently for mouse up events than it is for mouse wheel events since they end up with different frames for the same mouse positions.

Bob