A small library that helps you to make an amazing parallax view.



Using CocoaPods

Edit your Podfile and specify the dependency:

pod 'PVView', '~> 1.0.4'


  • iOS 9.0+
  • Swift 5


  • PVItemType presents a parallax item
  • PVActionType presents an action of an item
  • PVView is separated by pages
  • Each page contains a set of PVItemType, and PVView only updates actions of items on the current page
  • On a page, each PVItemType has a set of PVActionType
  • All PVActionType are updated by progress. Progress in a page is always in [0...1] range
  • An action may has startOffset and stopOffset. These parameters describe offsets on a page where the action will begin and finish. (0 <= startOffset < stopOffset <= 1)

How to use

1. Import PVView in proper place.

import PVView

2. Create parallax item by implementing PVItemType protocol.

enum YourItem: String, PVItemType {
    case item1
    case item2

    var identifier: String {
        return self.rawValue

3. Set PVView's delegate and implement PVViewDelegate protocol

Required delegate methods

There are 4 required methods of PVViewDelegate that you have to implement

  • Specify how many pages in PVView by implementing
func numberOfPages(in parallaxView: PVView) -> Int {
    return 2
  • Specify what items on a page by implementing
func parallaxView(_ parallaxView: PVView, itemsOnPage pageIndex: Int) -> [PVItemType] {
    return [YourItem.item1, .item2]
  • Then PVView will ask you what view will be attached to the item via:
func parallaxview(_ parallaxView: PVView, viewForItem item: PVItemType) -> UIView

Note: The view that is returned from this method will be cached for the item, and this method is only called when there is no view existed for the item in the cache

  • Finally, specify what actions will be run on an item by implementing:
func parallaxView(_ parallaxView: PVView, actionsOfItem item: PVItemType, onPage pageIndex: Int) -> [PVActionType] {
        if pageIndex == 0 {
            return [PVActionMove(fromOrigin: PVPoint(x: 50, y: 200), toOrigin: PVPoint(x: 250, y: 200))]
        return []

Note: In these methods, you can use currentPageIndex property of PVView to get index of page before the transition.

Optional delegate memthods

  • PVView supports both horizontal or vertical scrolling. Specify scroll direction of PVView by implementing below method (default will be horizontal):
func direction(of parallaxView: PVView) -> PVView.PVDirection
  • View of PVItemType will be automatically added as a subview of PVView by default. You can specify a container view for a view of PVItemType by implementing this method (return nil means container view is PVView)
func parallaxView(_ parallaxView: PVView, containerViewForItem item: PVItemType, onPage pageIndex: Int) -> UIView?
  • Before transition to a new page, PVView will call below method, it is your chance to do something before appearing the new page (ex: adding some animations on previous items or hiding/showing some views...)
func parallaxView(_ parallaxView: PVView, willBeginTransitionTo pageIndex: Int)
  • After finish transition to a new page, PVView will call below method, it is your chance to do something after appearing the new page (ex: setup initial state for actions of items...)
func parallaxView(_ parallaxView: PVView, didEndTransitionFrom previousPageIndex: Int?)
  • The last delegate method is:
func parallaxView(_ parallaxView: PVView, didUpdate pageProgress: Double, onPage pageIndex: Int)

This method is called continuously during scrolling to report progress in a page

4. Starting PVView



Action parameters

Action's parameters is present by PVParameters

  • startOffset: offset on page where the action will start at
  • stopOffset: offset on page where the action will stop at
  • timingFunction: an object that calculates action's progress base on a page progress


Action offsets

startOffset = 0.2, stopOffset = 0.6. The action will be started at progress = 0.2 and stoped at progress = 0.6

Timing function

Timing function

There is a built-in function called PVTimingFunction. It is same as CAMediaTimingFunction but provide us the evaluate method to calculate action's progress

You can init a PVTimingFunction by name that was defined in PVTimingFunctionName

To understand about those function names, please take a look at Ease functions

Action group

PVActionGroup presents a group of actions. Parameters of an action in the group is the parameters of the group.

Because PVActionGroup is a PVActionBasicType, so you can easily reverse all actions in the group by calling reverse method of the group

Reverse a sequence of actions

Sometime you want to reverse all actions in a sequence. There is a built in method can help:

public extension Sequence where Element: PVActionBasicType {
    func reversedActions(with newParameters: PVParameters = .default) -> [Element] {
        return self.map { $0.reverse(with: newParameters) }

Relative point and size

You can create an action with relative points using PVPoint, absolute point will be calculated base on size of the container view

PVActionMove(fromPosition: PVPoint(x: 2, y: 0.2, isRelative: true)

You can create an action with relative sizes using PVSize, absolute size will be calculated base on size of the container view

PVActionSize(from: PVSize(width: 0.2, height: 0.2, isRelative: true),
             to: PVSize(width: 0.4, height: 0.4, isRelative: true))


Customize action

You can easy custom any actions you want by implementing PVActionType

public protocol PVActionType {
    func update(_ progress: Double, target: UIView)

or implement PVActionBasicType that is inherited from PVActionType

public protocol PVActionBasicType: PVActionType {
    var parameters: PVParameters { get }
    func step(_ progress: Double, target: UIView)
    func reverse(with newParameters: PVParameters) -> Self

Example: I wrote a custom action called LetterSpacingAction. This action will change spacing of characters in a UILabel:

struct LetterSpacingAction: PVActionBasicType {
    let parameters: PVParameters
    let fromSpacing: Double
    let toSpacing: Double
    let maxWidth: CGFloat
    init(fromSpacing: Double, toSpacing: Double, maxWidth: CGFloat, parameters: PVParameters = .default) {
        self.fromSpacing = fromSpacing
        self.toSpacing = toSpacing
        self.maxWidth = maxWidth
        self.parameters = parameters
    func step(_ progress: Double, target: UIView) {
        guard let label = target as? UILabel else { return }
        let current = fromSpacing + (toSpacing - fromSpacing) * progress
        label.attributedText = NSAttributedString(string: label.text ?? "", attributes: [.kern : current])
        label.frame = CGRect(origin: label.frame.origin, size: label.sizeThatFits(CGSize(width: maxWidth, height: CGFloat.greatestFiniteMagnitude)))
    func reverse(with newParameters: PVParameters) -> LetterSpacingAction {
        return LetterSpacingAction(fromSpacing: toSpacing,
                                   toSpacing: fromSpacing,
                                   maxWidth: maxWidth,
                                   parameters: newParameters)

Customize timing function

You can create any timing functions by implementing PVTimingFunctionType

public protocol PVTimingFunctionType {
    func evaluate(_ input: Double) -> Double

Example: Creating an EaseOutSine function:

Ease out sine

struct EaseOutSineFunction: PVTimingFunctionType {
    func evaluate(_ input: Double) -> Double {
        return sin(input * Double.pi / 2)