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‎.gitignore‎

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# Xcode
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#
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# gitignore contributors: remember to update Global/Xcode.gitignore, Objective-C.gitignore & Swift.gitignore
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## Build generated
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build/
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DerivedData/
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## Various settings
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*.pbxuser
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!default.pbxuser
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*.mode1v3
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!default.mode1v3
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*.mode2v3
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!default.mode2v3
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*.perspectivev3
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!default.perspectivev3
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xcuserdata/
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## Other
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*.moved-aside
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*.xccheckout
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*.xcscmblueprint
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## Obj-C/Swift specific
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*.hmap
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*.ipa
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*.dSYM.zip
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*.dSYM
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## Playgrounds
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timeline.xctimeline
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playground.xcworkspace
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# Swift Package Manager
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#
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# Add this line if you want to avoid checking in source code from Swift Package Manager dependencies.
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# Packages/
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# Package.pins
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# Package.resolved
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.build/
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# CocoaPods
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#
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# We recommend against adding the Pods directory to your .gitignore. However
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# you should judge for yourself, the pros and cons are mentioned at:
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# https://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control
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#
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# Pods/
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# Carthage
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#
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# Add this line if you want to avoid checking in source code from Carthage dependencies.
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# Carthage/Checkouts
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Carthage/Build
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# fastlane
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#
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# It is recommended to not store the screenshots in the git repo. Instead, use fastlane to re-generate the
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# screenshots whenever they are needed.
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# For more information about the recommended setup visit:
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# https://docs.fastlane.tools/best-practices/source-control/#source-control
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fastlane/report.xml
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fastlane/Preview.html
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fastlane/screenshots/**/*.png
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fastlane/test_output

‎LICENSE‎

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BSD 2-Clause License
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Copyright (c) 2019, Tim Donnelly
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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1. Redistributions of source code must retain the above copyright notice, this
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list of conditions and the following disclaimer.
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2. Redistributions in binary form must reproduce the above copyright notice,
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this list of conditions and the following disclaimer in the documentation
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and/or other materials provided with the distribution.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

‎Package.swift‎

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// swift-tools-version:5.1
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// The swift-tools-version declares the minimum version of Swift required to build this package.
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import PackageDescription
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let package = Package(
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name: "DisplayLink",
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platforms: [
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.iOS(.v13),
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.tvOS(.v13)
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],
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products: [
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// Products define the executables and libraries produced by a package, and make them visible to other packages.
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.library(
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name: "DisplayLink",
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targets: ["DisplayLink"]),
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],
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dependencies: [
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// Dependencies declare other packages that this package depends on.
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// .package(url: /* package url */, from: "1.0.0"),
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],
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targets: [
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// Targets are the basic building blocks of a package. A target can define a module or a test suite.
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// Targets can depend on other targets in this package, and on products in packages which this package depends on.
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.target(
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name: "DisplayLink",
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dependencies: []),
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.testTarget(
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name: "DisplayLinkTests",
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dependencies: ["DisplayLink"]),
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]
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)

‎README.md‎

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# DisplayLink
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A Combine publisher with SwiftUI integration for `CADisplayLink`.
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SwiftUI does not currently provide any API to perform actions on a per-frame basis. This tiny
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library simplifies the work of bridging between `CADisplayLink` and SwiftUI:
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```swift
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import DisplayLink
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struct MyView: View {
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@State var offset: CGFloat = 0.0
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var body: some View {
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Color
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.red
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.frame(width: 40, height: 40)
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.offset(x: offset, y: offset)
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.onFrame { frame in
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self.offset += (frame.duration * 20.0)
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}
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}
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}
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```

‎Sources/DisplayLink/DisplayLink.swift‎

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import Foundation
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import QuartzCore
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import Combine
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// A publisher that emits new values when the system is about to update the display.
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public final class DisplayLink: Publisher {
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public typealias Output = Frame
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public typealias Failure = Never
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private let platformDisplayLink: PlatformDisplayLink
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private var subscribers: [CombineIdentifier:AnySubscriber<Frame, Never>] = [:] {
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didSet {
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dispatchPrecondition(condition: .onQueue(.main))
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platformDisplayLink.isPaused = subscribers.isEmpty
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}
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}
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fileprivate init(platformDisplayLink: PlatformDisplayLink) {
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dispatchPrecondition(condition: .onQueue(.main))
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self.platformDisplayLink = platformDisplayLink
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self.platformDisplayLink.onFrame = { [weak self] frame in
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self?.send(frame: frame)
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}
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}
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public func receive<S>(subscriber: S) where S : Subscriber, S.Failure == Never, S.Input == Frame {
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dispatchPrecondition(condition: .onQueue(.main))
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let typeErased = AnySubscriber(subscriber)
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let identifier = typeErased.combineIdentifier
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let subscription = Subscription(onCancel: { [weak self] in
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self?.cancelSubscription(for: identifier)
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})
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subscribers[identifier] = typeErased
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subscriber.receive(subscription: subscription)
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}
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private func cancelSubscription(for identifier: CombineIdentifier) {
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dispatchPrecondition(condition: .onQueue(.main))
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subscribers.removeValue(forKey: identifier)
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}
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private func send(frame: Frame) {
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dispatchPrecondition(condition: .onQueue(.main))
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let subscribers = self.subscribers.values
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subscribers.forEach {
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_ = $0.receive(frame) // Ignore demand
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}
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}
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}
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extension DisplayLink {
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// Represents a frame that is about to be drawn
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public struct Frame {
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// The system timestamp for the frame to be drawn
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public var timestamp: TimeInterval
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// The duration between each display update
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public var duration: TimeInterval
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}
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}
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extension DisplayLink {
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@available(iOS 13.0, tvOS 13.0, *)
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public convenience init() {
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self.init(platformDisplayLink: CADisplayLinkPlatformDisplayLink())
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}
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}
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extension DisplayLink {
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public static let shared = DisplayLink()
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}
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extension DisplayLink {
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fileprivate final class Subscription: Combine.Subscription {
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var onCancel: () -> Void
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init(onCancel: @escaping () -> Void) {
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self.onCancel = onCancel
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}
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func request(_ demand: Subscribers.Demand) {
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// Do nothing – subscribers can't impact how often the system draws frames.
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}
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func cancel() {
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onCancel()
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}
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}
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}
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fileprivate protocol PlatformDisplayLink: class {
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var onFrame: (DisplayLink.Frame) -> Void { get set }
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var isPaused: Bool { get set }
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}
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@available(iOS 13.0, tvOS 13.0, *)
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final class CADisplayLinkPlatformDisplayLink: PlatformDisplayLink {
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private var displayLink: CADisplayLink!
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var onFrame: (DisplayLink.Frame) -> Void = { _ in }
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var isPaused: Bool {
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get { displayLink.isPaused }
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set { displayLink.isPaused = newValue }
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}
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init() {
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displayLink = CADisplayLink(target: self, selector: #selector(displayLinkDidFire(_:)))
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displayLink.add(to: RunLoop.main, forMode: .common)
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displayLink.isPaused = true
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}
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@objc private func displayLinkDidFire(_ link: CADisplayLink) {
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let frame = DisplayLink.Frame(
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timestamp: link.timestamp,
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duration: link.duration)
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onFrame(frame)
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}
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}

‎Sources/DisplayLink/OnFrame.swift‎

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import SwiftUI
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import Combine
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extension SwiftUI.View {
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public func onFrame(isActive: Bool = true, displayLink: DisplayLink = .shared, _ action: @escaping (DisplayLink.Frame) -> Void) -> some View {
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let publisher = isActive ? displayLink.eraseToAnyPublisher() : Empty<DisplayLink.Frame, Never>().eraseToAnyPublisher()
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return SubscriptionView(content: self, publisher: publisher, action: action)
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}
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}

‎Tests/DisplayLinkTests/DisplayLinkTests.swift‎

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import XCTest
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@testable import DisplayLink
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final class DisplayLinkTests: XCTestCase {
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func testExample() {
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// This is an example of a functional test case.
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// Use XCTAssert and related functions to verify your tests produce the correct
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// results.
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XCTAssertEqual("Hello, World!", "Hello, World!")
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}
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static var allTests = [
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("testExample", testExample),
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]
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}

‎Tests/DisplayLinkTests/XCTestManifests.swift‎

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import XCTest
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#if !canImport(ObjectiveC)
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public func allTests() -> [XCTestCaseEntry] {
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return [
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testCase(DisplayLinkTests.allTests),
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]
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}
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#endif

‎Tests/LinuxMain.swift‎

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import XCTest
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import DisplayLinkTests
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var tests = [XCTestCaseEntry]()
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tests += DisplayLinkTests.allTests()
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XCTMain(tests)

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