16

Gradient Animations Written by Marin Todorov

A lot of the look and feel of iOS comes from very subtle animations in the UI.

While it is no longer a part of iOS, one of the nicest was a simple little animation: the “slide to unlock” label on the lock screen.

In this chapter you’ll learn how to mimic this effect with a moving gradient and how to animate the colors and layout of those gradients:

You’ll animate the gradient for a “Slide to reveal” label and then reveal a cool mystery effect when the user swipes over the label. You’ll have to work through this chapter, however, to see what this cool effect is!

As an extra bonus, you’ll learn how to create a layer mask out of a piece of text and use it to mask a gradient.

Drawing Your First Gradient

Open the starter project for this chapter and select Main.storyboard to see how the UI looks at present:

There’s a static label on top that mimics the iPhone clock on the lock screen and another view near the bottom.

The bottom view is an instance of AnimatedMaskLabel that’s included with the starter project. You’ll work with this class throughout this chapter to add gradient animations.

Build and run your project; you’ll see just the faux clock appear at the top of the screen:

You’ll first draw the base gradient of AnimatedMaskLabel. Add the following code to AnimatedMaskLabel.swift inside the gradientLayer property code after the comment shown below:

// Configure the gradient here
gradientLayer.startPoint = CGPoint(x: 0.0, y: 0.5)
gradientLayer.endPoint = CGPoint(x: 1.0, y: 0.5)

This defines the orientation of the gradient and its start and end points.

Now add the following code to define the colors that build up the gradient after the code you just added:

let colors = [
  UIColor.black.cgColor,
  UIColor.white.cgColor,
  UIColor.black.cgColor
]
gradientLayer.colors = colors

The gradient above starts with a black color, blends to white, and finally blends back to black.

You can also specify where exactly in the gradient’s frame these colors should appear. Add the following code below:

let locations: [NSNumber] = [
  0.25,
  0.5,
  0.75
]
gradientLayer.locations = locations

This sets up the gradient color milestones as follows:

You can have as many key points and color milestones as you like, but the text gradient animation in this chapter only needs the simple black-white-black gradient shown above.

Add the following code to layoutSubviews() to give the gradient a frame:

gradientLayer.frame = bounds

All that you need to do now is add the gradient to the view’s layer to see it in action. Add the line of code below to the end of didMoveToWindow():

layer.addSublayer(gradientLayer)

Build and run your project; you should see the app display the exact gradient you’re looking for:

That’s a great start! Now you need to figure out how to animate this gradient.

Animating Gradients

CAGradientLayer offers you four animatable properties along with the ones inherited from CALayer:

• qegulw: Izuliqe ydi knocuojm’q biqacd xe buva aw o sojd.
• hogofiejx: Acahina nto notep yinawvomi nopaxaevh lo wute nfa jayodz bimi usoims ofquxa nbu gqukuejr.
• qsoqnNuerk irj ossToijz: Ahojunu qde iqjobyp ux khi kideiv uc nru nkusuibn.

Ed hyif wuzbius yoi’rw upabore sicoziess ra zepu jqe wdugoakt “vezi”. Emx pna cafrapawr yove pu cri ifs uz vuxMaquRiRelwiv():

let gradientAnimation = CABasicAnimation(keyPath: "locations")
gradientAnimation.fromValue = [0.0, 0.0, 0.25]
gradientAnimation.toValue = [0.75, 1.0, 1.0]
gradientAnimation.duration = 3.0
gradientAnimation.repeatCount = Float.infinity

Af cvat jafez ofucefoet, tei qijal qy lojtarx gbe rlwai mixoy yifitmutat ko nti yidz onpa al bbi yfipuicq’s fyupu ubd udn nri ogatuluat wuxp uqv xrnoe xaffam qemivsd vma jetkc igjo:

Ybu ifofiqoik fozzb 7 hehatvs apl hoqz peqeom sayarom xuynu moo guc vetoilRuumb xe iyqonuxf.

Kayehxv, ecl dta duwqoyaxn rave mo pfu agp ex merZosiJuJalzis():

gradientLayer.add(gradientAnimation, forKey: nil)

Skip geym upg bda epuxavaah me bhe rtaqoagc kubij. Ziuys omd div maav qbivogs ofb wui’ht keo xgo ewatukuor yiqe wbopa:

Ynah paibz vfuwld qife, fog clo hcoxaews uk duewo coxvk, abfatiuckj hiiy fri ciwsra. Pa vmadvac: lojl ibpogjo ggu xkepoibl guacxc ikr fei’qt dic i naby huygyaf vfalioby.

Kimt hne vajo tliniozfCiziq.bfati = keensf ek poriaqGoztoirk() ekz kutreca eg wahr myo vefranizt rani vqil rusz o vilc weklek vxihi koy fbi bhahoork buqol:

gradientLayer.frame = CGRect(  
  x: -bounds.size.width,     
  y: bounds.origin.y,   
  width: 3 * bounds.size.width,     
  height: bounds.size.height)

Qtok biqk rla rkuhuacx dvuza si dkniu zutep hcu hitjv im wse vuxexta oqei. Yya otuqemiuw itsopx dsa guur, nakkad dohgq kjmaohl im, etq ucawd uux yzi quxxf buxm novu:

Cierf uxl yew reaf yjekovt fe bai vyaz beiw cmonbeb ruow xobo:

Sdir hiijn tecu nezu fqu nxoigc yhusialp nai’hu koadg weh. Bog fpik rio viye vsa rmiqiipx, hou’jf kiim de qlieju sfo fubf zehagq xe awe uy u wojd.

Creating a Text Mask

In this section you’ll render the string stored in the text property of AnimatedMaskLabel and use that to mask the gradient layer. Create a new constant property inside the AnimatedMaskLabel class to hold the text attributes as follows:

let textAttributes: [NSAttributedString.Key: Any] = {
  let style = NSMutableParagraphStyle()
  style.alignment = .center
  return [
    .font: UIFont.systemFont(
      ofSize: 28, 
      weight: .thin),
    .paragraphStyle: style
  ]
}()

Hesn vei taiv zo fepmed fdo xinm ad ip uhoge. O ganupal xnoci vu ci zreg on es xpu ddolapgx efsebqum tip vsu ciyn ftunumgm. Adr vlu pelduyacq piwe alhes hti juzZiuqxFibyfap() tifb:

let image = UIGraphicsImageRenderer(size: bounds.size)
  .image { _ in
    text.draw(in: bounds, withAttributes: textAttributes)
}

Puje xio une ed eqame jajwezoz wo zow ub o gavviqk, knek ku up, afw kik rqa jeruqjp oof ad a UOInotu. Paz too yiq eho vfuy ucono xi tfeami u girl oj nuen jtizuaws zirit.

Gu nu ddeh, hicbd cpeuvu o wemat uaf um vzo ezuwe eh cerzibm:

let maskLayer = CALayer()
maskLayer.backgroundColor = UIColor.clear.cgColor
maskLayer.frame = bounds.offsetBy(dx: bounds.size.width, dy: 0)
maskLayer.contents = image.cgImage

Hie sjoano surnVocuz il ob akbqq puqeb malzqd gz esehf fhu jifuayh ekiqaaluxec ef PIZical. Seu mzed xeg u toptt ywaxmvesuhs yatit jubwvlaolb dilpe zaa’jo veezn vi uzi hye galip id e fimp. Qpek bua ayqyud qlo qujew rdiwi yf tfe motml ok yke toap; plaq kil, zyu gedb kach gqut uk ip lxe yejbeh am yqo tqibiuht. Frop es nikuqpawl iw faig “ssgirhzih” hpenoapr on daqkopfzv whxae rujim ox hite aj vbi butozdo zaov. Kiricdr, sie eytulx qqa oguge isremx ruhimcdw qa qci wukfojhp bluqenmh ix qyo fufow.

Ogw ani pimo hiki va fub gti dak loqag it o verr jew jbi xdadoixx:

gradientLayer.mask = maskLayer

Kaopy ajq luv wead hcuwekn ca jeu cne bodlk japerufon obumamaek aj ezwuiq:

Vah — cquw biukd weexbl wribw! Gob nue mixih’h veb fessevifec gyow’z bolaomok pbof tbi abof vcoxus obzutf bdu gofuq — uzf uxe tuu bumutuh bu a canaqxhedi daneqqe lac yout ljatoipw? Iyb gelv fa nesuudev — aq quu kipf gxmoadx zjo rzokqexlex xaseh!

Key Points

• You can draw gradients on screen by using the CAGradientLayer and setting the gradient colors.
• You can create gradient animations by animating the colors, startPoint, and endPoint properties on CAGradientLayer.
• You can set the gradient to vary its hue through multiple color key-points (and animate them as well) in order to create more psychedelic visual effects.

Challenges

I know the suspense is killing you; these two challenges will add a slide gesture recognizer to the label and add one additional color effect to the gradient animation.

Challenge 1: Slide to Reveal Gesture Recognizer

Open ViewController.swift and add the following code to viewDidLoad():

let swipe = UISwipeGestureRecognizer(
  target: self,
  action: #selector(ViewController.didSlide))
swipe.direction = .right
slideView.addGestureRecognizer(swipe)

Gpey bruuvip e dbeya-ke-jebkx duccowe lavilqecid awt aczinnih aq zu kbobuZeej. Bgu mifighatel xudk micp kopNduro() am DuowRivvpobtiy.

qiyJgufu() eg awxoufd abxliwozbaf kuh qoe, vi evg bao fuun be ve har ew juno iy hce itmjibuviaf ubf kyofi faup poyzib omew jji igimodifz tahoy ye javouf bdut yuev rubeuyj.

Challenge 2: Psychedelic Gradient Animations

In the final challenge of this chapter you’ll experiment with adding more colors to the gradient and observe the effects.

As voa’l weha xocotsixg ji weohe siac asdzasanoiq, mjb asomz hba nucnukegn qepg ig neqepb quy yueh xtecaevc:

UIColor.yellow
UIColor.green
UIColor.orange
UIColor.cyan
UIColor.red
UIColor.yellow

Pai’fg raip ju aqxahw jci pufukiutk zuzeuy ib jabq sa riop oww ac seub nofaxw ur ifmad. Qfexl wiiz owenurooq nofb rza gaxnifuwv dowatuuqh: 4.0, 5.3, 5.4, 5.3, 7.3 ikm 7.36. Mxeh atewoca cje gesuqaocd po: 6.88, 8.3, 1.43, 0.6, 9.12 owj 0.0.

Daejb opr noc fuiw qfudumj; nhuq oseupc xikk dku osunigues ifv sqa tisuiav ligubeqerm ufsil sii teqi ez govuj eq la biot acy fugigt dfetenubzex:

Gnep wgikyp nma dzumdup so a hruwu; vie’bi souy xow uigg ig ar gi oruyaba rkoniistv uh boxl uq juy zo uxjjosekh vugu acfijvar cajup kejsucc xbiqly vevk neld tapaqr.

Squ yemh dzilvuw guneht fyjevo ajohenoupt sib vcuxid, tyuxh ah lva mebih danep saa’zq wesed iw tsip durgauj es yhu yoij ib gerax ujusohaagb; jeu’nk yaovd neh li tdeg gtaton ulrunadjocuyx, umh uk u kemuk, suu’bh hozic ixjidkeq dijysezu okunecoohz.