bjhomer · July 14, 2021 18:51 · bjhomer · Jul 29, 2014 · orta · Aug 21, 2014
diff --git a/movewindow.m b/movewindow.m
 // You might think that a view could trigger window movement by overriding -[NSView mouseDownCanMoveWindow]

 @interface DraggyView : NSView
 @end

 @implementation DraggyView
 - (BOOL)mouseDownCanMoveWindow {
    return YES;
 }
 @end

 // This probably doesn't do what you think it does, though. Specifically, it does not cause
 // a mouseDragged: event to be turned into a window drag. The real API for allowing events to
 // drag the window is this one:

 @interface NSWindow : NSReponder
 @property (getter=isMovableByWindowBackground) BOOL movableByWindowBackground;
 @end

 // This allows mouse events that propagate all the way up to the window (because they are
 // not intercepted by some other view) to initiate a window drag. By default, opaque windows
 // block mouse events from propagating up, and non-opaque views allow them to propagate.
 //
 // This is the behavior that is controlled by -mouseDownCanMoveWindow. If that returns YES
 // (as it does by default from non-opaque views), then the mouse event will move up to the
 // next view under the mouse. If NONE of the views that were under the mouse blocked it (by
 // returning NO from -mouseDownCanMoveWindow), then the mouse event will reach the window
 // background, and that can trigger dragging the window.
 //
 // However, note that this depends on every view in the view hierarchy cooperating to allow
 // the event to propagate. If any view in the way handles those events for itself, then the
 // event will not reach the window background, and the window drag will not be initiated.
 //
 // This is difficult in the Yosemite world where developers are allowed to create their own
 // titlebar-like views (using NSVisualEffectMaterialTitlebar), because even though the view
 // *looks* like a titlebar, it still propagates its events up the view hierarchy. There is
 // no way for a view to say "I don't care what other views are under the mouse right now --
 // I just want this event to initiate a window drag."
 //
 // Or, at least, if such an API exists, I haven't found it.
	// You might think that a view could trigger window movement by overriding -[NSView mouseDownCanMoveWindow]

	@interface DraggyView : NSView
	@end

	@implementation DraggyView
	- (BOOL)mouseDownCanMoveWindow {
	return YES;
	}
	@end

	// This probably doesn't do what you think it does, though. Specifically, it does not cause
	// a mouseDragged: event to be turned into a window drag. The real API for allowing events to
	// drag the window is this one:

	@interface NSWindow : NSReponder
	@property (getter=isMovableByWindowBackground) BOOL movableByWindowBackground;
	@end

	// This allows mouse events that propagate all the way up to the window (because they are
	// not intercepted by some other view) to initiate a window drag. By default, opaque windows
	// block mouse events from propagating up, and non-opaque views allow them to propagate.
	//
	// This is the behavior that is controlled by -mouseDownCanMoveWindow. If that returns YES
	// (as it does by default from non-opaque views), then the mouse event will move up to the
	// next view under the mouse. If NONE of the views that were under the mouse blocked it (by
	// returning NO from -mouseDownCanMoveWindow), then the mouse event will reach the window
	// background, and that can trigger dragging the window.
	//
	// However, note that this depends on every view in the view hierarchy cooperating to allow
	// the event to propagate. If any view in the way handles those events for itself, then the
	// event will not reach the window background, and the window drag will not be initiated.
	//
	// This is difficult in the Yosemite world where developers are allowed to create their own
	// titlebar-like views (using NSVisualEffectMaterialTitlebar), because even though the view
	// looks like a titlebar, it still propagates its events up the view hierarchy. There is
	// no way for a view to say "I don't care what other views are under the mouse right now --
	// I just want this event to initiate a window drag."
	//
	// Or, at least, if such an API exists, I haven't found it.