Handling Mouse Events
Categories: Adventure Game
In this series of posts I describe the process I've followed, as an amateur game designer, for developing an adventure game written in Swift using the SpriteKit framework for iOS.
Introduction
Last week, I implemented the callbacks for handling touch events on iOS and tvOS. This week, I’m implementing a callback for handling mouse events on macOS.
Moving the Cursor (on macOS)
The only method I need to override for now is mouseMoved, which informs the receiver that the mouse has moved. Each function call updates the position of the cursor node with the relative position of the mouse in the game scene:
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#if os(OSX)
// Mouse-based event handling
extension GameScene {
override func mouseMoved(with event: NSEvent) {
cursor.position = event.location(in: self)
}
}
#endif
The code is straightforward, but as soon as I build the app for the macOS target, I receive this compilation error:
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GameScene.swift: Use of unresolved identifier 'nextPosition'
This error occurs because in the touchHandler method, I’ve defined nextPosition only if either os(iOS) or os(tvOS) is true, but it’s still being used even when the target is macOS. To fix this issue, I can wrap the entire method definition in a #if os(iOS) || os(tvOS) block to conditionally compile that portion of the code only when the target is either iOS or tvOS:
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#if os(iOS) || os(tvOS)
private func touchHandler(_ location: CGPoint) {
// ...
}
#endif
Once this error is fixed, the app builds successfully. The app starts, a window appears on the screen, I move the mouse, and… nothing happens. :(
The cursor remains at the center of the game scene.
After a brief search, I found the solution: I’m missing a tracking area!
A tracking area is:
A region of a view that generates mouse-tracking and cursor-update events when the pointer is over that region.
The game’s tracking area covers the entire game scene and has the scene as its owner.
I added this code in setUpScene and wrapped it in a conditional compilation block that checks if os(macOS) is true:
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#if os(OSX)
// Create a tracking area object with self as the owner
// (i.e., the recipient of mouse-tracking messages)
if let frame = view?.frame {
let trackingArea = NSTrackingArea(
rect: frame,
options: [.activeInKeyWindow, .mouseMoved],
owner: self,
userInfo: nil
)
// Add the tracking area to the view
view?.addTrackingArea(trackingArea)
}
#endif
This is the final result:
Hiding the Default Cursor
In the video above, you’ll notice that both cursors—the default macOS cursor and the game cursor—are visible when the mouse is in the game window.
I would like to hide the default cursor as soon as the mouse enters the game’s tracking area and reveal it when the mouse exits the tracking area.
To hide/unhide the cursor, one can call NSCursor.hide()/NSCursor.unhide(), so I first attempted to implement two more NSResponder event callbacks: mouseEntered/mouseExited:
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override func mouseEntered(with event: NSEvent) {
// Hide the default cursor
NSCursor.hide()
}
override func mouseExited(with event: NSEvent) {
// Show the default cursor
NSCursor.unhide()
}
For some reason, these callbacks never run.
I searched for a solution, but I couldn’t find anything that doesn’t involve subclassing the main game view (SKView), so I’ve decided to leave it as is for now. I plan to revisit and fix this issue later. :)
Conclusion
Now the app can react to mouse events by moving the cursor on the screen. However, there remains the issue that both the default cursor and the game cursor are visible within the game tracking area. I intend to address this later.
In the next post, I’ll create the first sprite node for displaying the scene background.