Use Constraints to Limit Movement
At the moment, the player node moves to the tap location instead of staying on the platform. There’s a way to fix this problem using constraints and the SKConstraint class.
With constraints, you can restrict a node’s movement to a specific area. In this case, you need to limit the player.position.y value to keep Blob firmly on the platform.
Open the Player.swift file and add a new method above the walk() method:
| | func setupConstraints(floor: CGFloat) { |
| | let range = SKRange(lowerLimit: floor, upperLimit: floor) |
| | let lockToPlatform = SKConstraint.positionY(range) |
| | |
| | constraints = [ lockToPlatform ] |
| | } |
This new method sets up a range with an upper and lower limit using the values you pass in for the lowerLimit and upperLimit parameters.
Go back to the GameScene.swift file, and where you set up the player node, add the following line above the line that adds that node to the scene:
| | player.setupConstraints(floor: foreground.frame.maxY) |
This line of code calls the new method and passes in the foreground frame’s maxY value, which it uses to keep the player node’s position.y value constrained to the platform.
Build and run the project, and tap anywhere you’d like.
Notice that no matter where you tap, Blob stays firmly planted on top of the platform. But don’t celebrate yet. You need to work out the next problem: Blob’s inability to pay attention to where he’s going. Silly, Blob, what are you thinking?