Sprite Kit set Min. and Max. for Jump

Question

I want to move a SKSpriteNode on the Y-Axis. The SKSpriteNode called Player has no Velocity.The Player can only jump if a Platform is in contact.

Answer 1

Here is an working example on how to make something like:

• long pressed jump based on duration of press
• short (one tap jump)
• restrict character to jump while in the air
• keep character jumping while finger is on screen

Code (Swift 4.x)

import SpriteKit

struct Constants {
    static let minimumJumpForce:CGFloat = 15.0
    static let maximumJumpForce:CGFloat = 30.0
    static let characterSideSpeed:CGFloat = 18.0
}

class GameScene: SKScene,SKPhysicsContactDelegate
{
    let CharacterCategory   : UInt32 = 0x1 << 1
    let PlatformCategory    : UInt32 = 0x1 << 2
    let WallCategory        : UInt32 = 0x1 << 3

    var force: CGFloat = 16.0 //Initial force
    var pressed = false
    var isCharacterOnGround = false // Use this to prevent jumping while in the air
    let character = SKSpriteNode(color: .green, size: CGSize(width: 30, height:30))
    let debugLabel = SKLabelNode(fontNamed: "Geneva")

    override func didMove(to view: SKView)
    {
        //Setup contact delegate so we can use didBeginContact and didEndContact methods
        physicsWorld.contactDelegate = self
        physicsWorld.speed = 0.5
        //Setup borders so character can't escape from us :-)
        self.physicsBody = SKPhysicsBody(edgeLoopFrom: self.frame)
        self.physicsBody?.categoryBitMask = WallCategory
        self.physicsBody?.collisionBitMask = CharacterCategory

        //Setup character
        character.position = CGPoint(x: 150, y: 150)
        character.physicsBody = SKPhysicsBody(rectangleOf: character.size)
        character.physicsBody?.categoryBitMask = CharacterCategory
        character.physicsBody?.contactTestBitMask = PlatformCategory
        character.physicsBody?.collisionBitMask = PlatformCategory | WallCategory
        character.physicsBody?.allowsRotation = false
        character.physicsBody?.isDynamic = true
        character.physicsBody?.restitution = 0.1

        self.addChild(character)

        generatePlatforms()

        debugLabel.text = " DEBUG: "
        debugLabel.fontColor = .white
        debugLabel.fontSize = 12.0
        debugLabel.position = CGPoint(x: frame.midX, y: frame.midY+100)
        self.addChild(debugLabel)
    }

    func generatePlatforms(){
        for i in 1...4
        {
            let position = CGPoint(x: frame.midX, y: CGFloat(i)*140.0 - 100)
            let platform = createPlatformAtPosition(position: position)
            self.addChild(platform)
        }
    }


    func createPlatformAtPosition(position : CGPoint)->SKSpriteNode{

        let platform = SKSpriteNode(color: .green, size: CGSize(width: frame.size.width, height:20))

        platform.position = position

        platform.physicsBody = SKPhysicsBody(
            edgeFrom: CGPoint(x: -platform.size.width/2.0, y:platform.size.height/2.0),
            to:CGPoint(x: platform.size.width/2.0, y: platform.size.height/2.0))

        platform.physicsBody?.categoryBitMask       = PlatformCategory
        platform.physicsBody?.contactTestBitMask    = CharacterCategory
        platform.physicsBody?.collisionBitMask      = CharacterCategory
        platform.physicsBody?.allowsRotation        = false
        platform.name                               = "platform"
        platform.physicsBody?.isDynamic             = false
        platform.physicsBody?.restitution           = 0.0

        return platform
    }

    func jump(force : CGFloat){
        if(self.isCharacterOnGround){
            self.character.physicsBody?.applyImpulse(CGVector(dx: 0, dy: force))
            self.character.physicsBody?.collisionBitMask = WallCategory
            self.isCharacterOnGround = false
        }
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        self.pressed = true

        let timerAction = SKAction.wait(forDuration: 0.05)

        let update = SKAction.run({
            if(self.force < Constants.maximumJumpForce){
                self.force += 2.0
            }else{
                self.jump(force: Constants.maximumJumpForce)
                self.force = Constants.maximumJumpForce
            }
        })

        let sequence = SKAction.sequence([timerAction, update])
        let repeat_seq = SKAction.repeatForever(sequence)
        self.run(repeat_seq, withKey:"repeatAction")
    }


    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {

        self.removeAction(forKey: "repeatAction")
        self.jump(force: self.force)
        self.force = Constants.minimumJumpForce
        self.pressed = false

    }

    override func update(_ currentTime: TimeInterval) {

        debugLabel.text = "DEBUG: onTheGround : \(isCharacterOnGround), force \(force)"

        if(character.position.x <= character.size.width/2.0 + 5.0 && character.physicsBody!.velocity.dx < 0.0 ){
            character.physicsBody?.applyForce(CGVector(dx: Constants.characterSideSpeed, dy: 0.0))
        }else if((character.position.x >= self.frame.size.width - character.size.width/2.0 - 5.0) && character.physicsBody!.velocity.dx >= 0.0){
            character.physicsBody?.applyForce(CGVector(dx: -Constants.characterSideSpeed, dy: 0.0))
        }else if(character.physicsBody!.velocity.dx > 0.0){
            character.physicsBody!.applyForce(CGVector(dx: Constants.characterSideSpeed, dy: 0.0))
        }else{
            character.physicsBody!.applyForce(CGVector(dx: -Constants.characterSideSpeed, dy: 0.0))
        }
    }

    func didBegin(_ contact: SKPhysicsContact) {

        var firstBody, secondBody: SKPhysicsBody

        if contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask {
            firstBody = contact.bodyA
            secondBody = contact.bodyB
        } else {
            firstBody = contact.bodyB
            secondBody = contact.bodyA
        }

        if ((firstBody.categoryBitMask & CharacterCategory) != 0 &&
            (secondBody.categoryBitMask & PlatformCategory != 0)) {


            let platform = secondBody.node! as! SKSpriteNode
            //  platform.color = UIColor.redColor()
            let platformSurfaceYPos = platform.position.y + platform.size.height/2.0

            let player = contact.bodyB.node! as! SKSpriteNode
            let playerLegsYPos = player.position.y - player.size.height/2.0

            if((platformSurfaceYPos <= playerLegsYPos)){
                character.physicsBody?.collisionBitMask = PlatformCategory | WallCategory
                self.isCharacterOnGround = true

                if(self.pressed){
                    let characterDx = character.physicsBody?.velocity.dx
                    character.physicsBody?.velocity = CGVector(dx: characterDx!, dy: 0.0)
                    self.jump(force: Constants.maximumJumpForce)
                }
            }
        }
    }

    func didEnd(_ contact: SKPhysicsContact) {

        var firstBody, secondBody: SKPhysicsBody

        if contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask {
            firstBody = contact.bodyA
            secondBody = contact.bodyB
        } else {
            firstBody = contact.bodyB
            secondBody = contact.bodyA
        }

        if ((firstBody.categoryBitMask & CharacterCategory) != 0 &&
            (secondBody.categoryBitMask & PlatformCategory != 0)) {

            let platform = secondBody.node as! SKSpriteNode
            let platformSurfaceYPos = platform.position.y + platform.size.height/2.0

            let player = contact.bodyB.node as! SKSpriteNode
            let playerLegsYPos = player.position.y - player.size.height/2.0

            if((platformSurfaceYPos <= playerLegsYPos) && ((character.physicsBody?.velocity.dy)! > CGFloat(0.0))){
                character.physicsBody?.collisionBitMask = WallCategory
                self.isCharacterOnGround = false
            }
        }
    }
}

Note that this is simple example, and in real application you will probably have to handle states like isOnTheGround in a different way. Right now, to determine if character is on the ground you just set isOnTheGround = true when character make a contact with platform, and set it to false in didEndContact...But there are situations when character can be in contact with platform while in the air (eg. side contact)...

EDIT:

I changed the code to let the player jump while pressed. Here is the result:

Important:

Actual platform implementation and contact handling is up to you and this is not tested. The only purpose of this example is to show you how to jump while pressed. Currently, physicsWorld.speed is set to 0.5 to make animation slower because its easier to debug like that, but you can change this to default value (1.0).

So, as you can see from the image, while player is on the first platform some small jumps are presented (by simple tapping, or short pressing). Then (player is still on first platform) long press has been made, and player has jumped on second platform. After that, another long press is done, but this time without releasing, and player starts jumping from one platform to another using maximum force.

This needs a lot of tweaking and proper platform & contact detection, but it can give you an idea about how to implement jumping you asked about.