Merge pull request #1 from fermoya/rotation-effect

Rotation effect

README.md

@@ -63,7 +63,9 @@ whereas a value greater than one will make it look like a box:
 
 <img src="resources/page_aspect_ratio_greater_than_1.png" alt="PageAspectRatio greater than 1" height="640"/>
 
-You can also use `interactive` to pass a shrink ratio that will be applied to those components that are not focused, that is, those elements whose index is different from `pageIndex` binding:
+### Animations
+
+Use `interactive` to pass a shrink ratio that will be applied to those components that are not focused, that is, those elements whose index is different from `pageIndex` binding:
 
 ```swift
 Pager(...)
@@ -72,6 +74,16 @@ Pager(...)
 
 <img src="resources/interactive-pager.gif" alt="Interactive pager"/>
 
+You can also use `rotation3D` to add a rotation effect to your pages:
+
+```swift
+Pager(...)
+    .itemSpacing(10)
+    .rotation3D()
+```
+
+<img src="resources/rotation3D.gif" alt="PageAspectRatio lower than 1" height="640"/>
+
 ### Gestures
 
 `Pager` comes with the following built-in gestures:

Sample.xcodeproj/project.xcworkspace/xcshareddata/swiftpm/Package.resolved

@@ -6,7 +6,7 @@
         "repositoryURL": "https://github.com/fermoya/SwiftUIPager.git",
         "state": {
           "branch": "master",
-          "revision": "fb221c6d2305c05b8ba7d1c2911d19082b9ec1c1",
+          "revision": "1d22a5878394697884a4b15215522e04a68f835c",
           "version": null
         }
       }

Sources/SwiftUIPager/Pager+Buildable.swift

@@ -12,12 +12,22 @@ extension Pager: Buildable {
 
     /// Call this method to provide a shrink ratio that will apply to the items that are not focused.
     ///
-    /// - Parameter scale:      shrink ratio
-    /// - Note:                 `scale` must be lower than _1_, otherwise it defaults to _1_
+    /// - Parameter scale: shrink ratio
+    /// - Note: `scale` must be lower than _1_, otherwise it defaults to _1_
     public func interactive(_ scale: CGFloat) -> Self {
+        guard !shouldRotate else { return self }
         let scale = min(1, abs(scale))
         return mutating(keyPath: \.interactiveScale, value: scale)
     }
+
+    /// Call this method to add a 3D rotation effect.
+    ///
+    /// - Parameter value: `true` if the pages should have a 3D rotation effect
+    /// - Note: If you call this method, any previous or later call to `interactive` will have no effect.
+    public func rotation3D(_ value: Bool = true) -> Self {
+        mutating(keyPath: \.interactiveScale, value: rotationInteractiveScale)
+            .mutating(keyPath: \.shouldRotate, value: value)
+    }
 
     /// Provides an offset to modify the
     public func contentOffset(_ pageOffset: Double) -> Self {

Sources/SwiftUIPager/Pager+Helper.swift

@@ -104,6 +104,31 @@ extension Pager {
         return max(offsetUpperbound, min(offsetLowerbound, offset))
     }
 
+    /// Angle for the 3D rotation effect
+    func angle(for item: Data) -> Angle {
+        guard shouldRotate else { return .zero }
+        guard let index = data.firstIndex(of: item) else { return .zero }
+
+        let totalIncrement = abs(totalOffset / pageDistance)
+
+        let currentAngle = index == page ? .zero : index < page ? Angle(degrees: rotationDegrees) : Angle(degrees: -rotationDegrees)
+        guard isDragging else {
+            return currentAngle
+        }
+
+        let newAngle = direction == .forward ? Angle(degrees: currentAngle.degrees + rotationDegrees * Double(totalIncrement)) : Angle(degrees: currentAngle.degrees - rotationDegrees * Double(totalIncrement) )
+        return newAngle
+    }
+
+    /// Axis for the rotations effect
+    func axis(for item: Data) -> (CGFloat, CGFloat, CGFloat) {
+        guard shouldRotate else { return (0, 0, 0) }
+        guard let index = data.firstIndex(of: item) else { return (0, 0, 0) }
+
+        let currentXAxis: CGFloat = index == page ? 0 : index < page ? rotationAxis.x : -rotationAxis.x
+        return (currentXAxis, rotationAxis.y, rotationAxis.z)
+    }
+
     /// Scale that applies to a particular item
     func scale(for item: Data) -> CGFloat {
         guard isDragging else { return isFocused(item) ? 1 : interactiveScale }

Sources/SwiftUIPager/Pager.swift

@@ -45,6 +45,15 @@ public struct Pager<Data, Content>: View  where Content: View, Data: Identifiabl
     /// A ratio of 3, for instance, would mean the items held in memory are enough
     /// to cover 3 times the size of the pager
     let recyclingRatio = 4
+
+    /// Angle of rotation when should rotate
+    let rotationDegrees: Double = 20
+
+    /// Angle of rotation when should rotate
+    let rotationInteractiveScale: CGFloat = 0.7
+
+    /// Axis of rotation when should rotate
+    let rotationAxis: (x: CGFloat, y: CGFloat, z: CGFloat) = (0.2, 1, 0)
 
     /*** Dependencies ***/
 
@@ -58,6 +67,9 @@ public struct Pager<Data, Content>: View  where Content: View, Data: Identifiabl
 
     /// Shrink ratio that affects the items that aren't focused
     var interactiveScale: CGFloat = 1
+
+    /// `true` if pages should have a 3D rotation effect
+    var shouldRotate: Bool = false
 
     /// Used to modify `Pager` offset outside this view
     var contentOffset: CGFloat = 0
@@ -94,9 +106,9 @@ public struct Pager<Data, Content>: View  where Content: View, Data: Identifiabl
 
     /// Initializes a new Pager.
     ///
-    /// - Parameter page:       Binding to the index of the focused page
-    /// - Parameter data:       Array of items to populate the content
-    /// - Parameter content:    Factory method to build new pages
+    /// - Parameter page: Binding to the index of the focused page
+    /// - Parameter data: Array of items to populate the content
+    /// - Parameter content: Factory method to build new pages
     public init(page: Binding<Int>, data: [Data], @ViewBuilder content: @escaping (Data) -> Content) {
         self._page = page
         self.data = data
@@ -109,6 +121,8 @@ public struct Pager<Data, Content>: View  where Content: View, Data: Identifiabl
                 self.content(item)
                     .frame(size: self.pageSize)
                     .scaleEffect(self.scale(for: item))
+                    .rotation3DEffect(self.angle(for: item),
+                                      axis: self.axis(for: item))
                     .onTapGesture (perform: {
                         withAnimation(.spring()) {
                             self.scrollToItem(item)