How to accept a mouse click for one portion and let click-though the rest of an NSWindow

Question

I have the code below for a subclassed NSWindow, there is an animated view which can be scaled and I want to accept click when it is clicked at the right spot and reject (click through) if it is outside.

The code below works nice except the window does not let clicks through.

- (void)mouseDragged:(NSEvent *)theEvent {
  if (allowDrag) {
    NSRect screenVisibleFrame = [[NSScreen mainScreen] visibleFrame];
    NSRect windowFrame = [self frame];
    NSPoint newOrigin = windowFrame.origin;

    // Get the mouse location in window coordinates.
    NSPoint currentLocation = [theEvent locationInWindow];
    // Update the origin with the difference between the new mouse location and the old mouse location.
    newOrigin.x += (currentLocation.x - initialMouseLocation.x);
    newOrigin.y += (currentLocation.y - initialMouseLocation.y);

    if ((newOrigin.y + windowFrame.size.height) > (screenVisibleFrame.origin.y + screenVisibleFrame.size.height)) {
        newOrigin.y = screenVisibleFrame.origin.y + (screenVisibleFrame.size.height - windowFrame.size.height);
    }

    // Move the window to the new location
    [self setFrameOrigin:newOrigin];
  }
}



- (void)mouseDown:(NSEvent *)theEvent
{
    screenResolution = [[NSScreen mainScreen] frame];

   initialMouseLocation = [theEvent locationInWindow];

    float scale = [[NSUserDefaults standardUserDefaults] floatForKey:@"widgetScale"]/100;

    float pX = initialMouseLocation.x;
    float pY = initialMouseLocation.y;
    float fX = self.frame.size.width;
    float fY = self.frame.size.height;

    if (pX>(fX-fX*scale)/2 && pX<(fX+fX*scale)/2 && pY>(fY+fY*scale)/2) {
        allowDrag = YES;
    } else {
        allowDrag = NO;
    }
}

Answer 1

In Cocoa, you have two basic choices: 1) you can make a whole window pass clicks through with [window setIgnoresMouseEvents:YES], or 2) you can make parts of your window transparent and clicks will pass through by default.

The limitation is that the window server makes the decision about which app to deliver the event to once. After it has delivered the event to your app, there is no way to make it take the event back and deliver it to another app.

One possible solution might be to use Quartz Event Taps. The idea is that you make your window ignore mouse events, but set up an event tap that will see all events for the login session. If you want to make an event that's going through your window actually stop at your window, you process it manually and then discard it. You don't let the event continue on to the app it would otherwise reach. I expect that this would be very tricky to do right. For example, you don't want to intercept events for another app's window that is in front of yours.

If at all possible, I recommend that you use the Cocoa-supported techniques. I would think you would only want clicks to go through your window where it's transparent anyway, since otherwise how would the user know what they are clicking on?

Answer 2

Please invoke an transparent overlay CHILD WINDOW for accepting control and make the main window -setIgnoresMouseEvents:YES as Ken directed.

I used this tricky on my app named "Overlay".