ios - Gradually increasing speed of scrolling background in SpriteKit -

i making simple game in spritekit, , have scrolling background. happens few background images placed adjacent each other when game scene loaded, , image moved horizontally when scrolls out of screen. here code that, game scene's didmovetoview method.

// self.gamespeed 1.0 , gradually increases during game  let backgroundtexture = sktexture(imagenamed: "background") var movebackground = skaction.movebyx(-self.frame.size.width, y: 0, duration: (20 / self.gamespeed)) var replacebackground = skaction.movebyx(self.frame.size.width, y: 0, duration: 0) var movebackgroundforever = skaction.repeatactionforever(skaction.sequence([movebackground, replacebackground]))  var i:cgfloat = 0; < 2; i++ {     var background = skspritenode(texture: backgroundtexture)     background.position = cgpoint(x: self.frame.size.width / 2 + self.frame.size.width * i, y: cgrectgetmidy(self.frame))     background.size = self.frame.size     background.zposition = -100     background.runaction(movebackgroundforever)      self.addchild(background) } 

now want increase speed of scrolling background @ points of game. can see duration of background's horizontal scroll set (20 / self.gamespeed). not work, because code run once, , therefore movement speed never updated account new value of self.gamespeed variable.

so, question simply: how increase speed (reduce duration) of background images' movements according self.gamespeed variable?

thanks!

you use gamespeed variable set velocity of background. work, firstly, need have reference 2 background pieces (or more if wanted):

class gamescene: skscene {     lazy var backgroundpieces: [skspritenode] = [skspritenode(imagenamed: "background"),                                                   skspritenode(imagenamed: "background")]      // ...  } 

now need gamespeed variable:

var gamespeed: cgfloat = 0.0 {     // using property observer means can update speed of      // background setting gamespeed.     didset {         background in backgroundpieces {             // minus, because background moving left right.             background.physicsbody!.velocity.dx = -gamespeed         }     } } 

then position each piece correctly in didmovetoview. also, method work each background piece needs physics body can change velocity.

override func didmovetoview(view: skview) {     (index, background) in enumerate(backgroundpieces) {         // setup position, zposition, size, etc...          background.physicsbody = skphysicsbody(rectangleofsize: background.size)         background.physicsbody!.affectedbygravity = false         background.physicsbody!.lineardamping = 0         background.physicsbody!.friction = 0          self.addchild(background)     }      // if wanted give background , initial speed,     // here's place it.     gamespeed = 1.0 } 

you update gamespeed in update example gamespeed += 0.5.

finally, in update need check if background piece has gone offscreen (to left). if has needs moved end of chain of background pieces:

override func update(currenttime: cftimeinterval) {     background in backgroundpieces {         if background.frame.maxx <= 0 {             let maxx = maxelement(backgroundpieces.map { $0.frame.maxx })              // i'm assuming anchor of background (0.5, 0.5)             background.position.x = maxx + background.size.width / 2         }     } }