ios - Swift: Progress bar jumps when using showing progress -

the code below works if background , progress bar share same dimensions. if progress bar shorter, bar jumps around bit whenever there update -- if scaling progress bar changes origin progress bar.

what's right way implement custom progress bars in swift , spritekit?

private func initprogresslayer(gridleftx: cgfloat, gridwidth: cgfloat) {     // set progress bar width     var progresswidth = gridwidth     let barwidth = cgfloat(50)     let barheight = progressbarheight      // set layer position     let posy = statslayer.position.y - cgfloat(progressbarheight/2)     let posx = cgfloat(0.0) - cgfloat(progresswidth/2)     progresslayer.position = cgpoint(x: posx, y: posy)      // create background progress bar     let backgroundrect = cgrect(x: 0, y: 0, width: progresswidth, height: progressbarheight)     let background = skshapenode(rect: backgroundrect)     background.fillcolor = progressbackgroundcolor      // create progress bar     let barrect = cgrect(x: 10, y: 0, width: barwidth, height: barheight)     progressbar = skshapenode(rect: barrect)     progressbar.fillcolor = progressbarcolor      // add background , progress bar layer     progresslayer.addchild(background)     progresslayer.addchild(progressbar) }   private func updateprogress(var progress: cgfloat) {     if (progress > 1.0) {         progress = 1.0     }     let scaleaction = skaction.scalexto(progress, duration: nstimeinterval(0.3))     scaleaction.timingmode = .easein     progressbar.runaction(scaleaction) } 

check following:

• is updateprogress: being called background thread? (it shouldn't)
• how updateprogress: called? if enough might want remove scalex animation , apply scale directly sprite. in fact, might want try doing anyway, it's might causing issues.
• have shifted anchorpoint of progress bar sprite? create random behaviours when try , edit frame properties.