WPF 动画存在撕裂和闪烁

Question

我在 WPF 动画中遇到撕裂和闪烁问题。我有一个玩具应用程序可以演示这些问题。该应用程序在屏幕上呈现方块动画。方块的边缘出现撕裂现象，整个动画感觉不平滑。

Perforator 显示 >60fps、~10mb 视频内存、0 IRT。

我已经在两台新的高端计算机上尝试过此操作，并且都显示相同的糟糕动画（> 1gb vram、四核等）。

SimpleWindow.zip

Answer 1

您绝对确定您的代码正在运行硬件加速吗？请查看此列表：http://blogs.msdn.com/b/jgoldb/archive/2010/06/22/software-rendering-usage-in-wpf.aspx。

如果是这样 - 考虑到您拥有超酷的硬件 - 您可以尝试在 CPU 而不是 GPU 上运行它。您可以通过将 RenderMode 设置为 SoftwareOnly 来强制执行此操作（上面链接的列表中的第 6 项）

Answer 2

我向 WPF 团队提出了这个问题，总而言之，他们说他们认为动画平滑度存在一些可以改进的问题。

他们还补充道：

我们非常努力地安排我们的场景
与 VBlank 同步更新以获得
非常规律、可靠的动画。任何
UI 线程上的工作可能会干扰
艰难的。在这个例子中，他们是
使用 DispatcherTimers 进行调度
在 UI 线程上工作以创建新的
故事板、删除旧元素等。

的动画，对我来说看起来更流畅。特别感谢 Dwayne Need 提供此信息。

Answer 3

造成撕裂的原因是创建了许多必须由 UI 线程拥有的对象，并且所有这些调用以及将它们添加到 UI 容器都将通过主线程。

我什至尝试制作线程驱动版本而不是计时器，但这并没有改变任何内容，因为所有 FrameWorkElement 对象都必须使用 Dispatcher.Invoke 创建。

Storyboard 和 beginStoryboard + EventTrigger 的创建都必须在 Ui 线程上完成。这就是阻碍流畅性的原因。

不幸的是，这种设计无法实现无闪烁操作：/

using System;
using System.Linq;
using System.Threading;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Interop;
using System.Windows.Media;
using System.Windows.Shapes;
using System.Windows.Media.Animation;
using System.Windows.Threading;
using System.Collections.Generic;

namespace SimpleWindow
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow
    {
        readonly SolidColorBrush _fillBrush = new SolidColorBrush(Colors.CadetBlue);

        // Timers
        //private DispatcherTimer _addItemsTimer;
        //private DispatcherTimer _removeItemsTimer;
        private Thread _addItemsTimer;
        private Thread _removeItemsTimer;
        private volatile bool formClosing = false;

        private readonly TimeSpan _addInterval = TimeSpan.FromSeconds(0.21);
        private readonly TimeSpan _removeInterval = TimeSpan.FromSeconds(1);
        public MainWindow()
        {
            InitializeComponent();
            Closing += MainWindow_Closing;
            Loaded += OnLoaded;
        }

        void MainWindow_Closing(object sender, System.ComponentModel.CancelEventArgs e)
        {
            formClosing = true;
            //_addItemsTimer.Join();
            //_removeItemsTimer.Join();
        }

        private void OnLoaded(object o, RoutedEventArgs args)
        {
            _addItemsTimer = new Thread((ThreadStart)delegate() {
                while (!formClosing)
                {
                    Thread.Sleep(_addInterval);
                    AddItems();
                }
            });

            _removeItemsTimer = new Thread((ThreadStart)delegate()
            {
                while (!formClosing)
                {
                    Thread.Sleep(_removeInterval);
                    RemoveOffScreenItems();
                }
            });

            _addItemsTimer.SetApartmentState(ApartmentState.STA);
            _addItemsTimer.Start();
            _removeItemsTimer.SetApartmentState(ApartmentState.STA);
            _removeItemsTimer.Start();

            WindowState = WindowState.Maximized;
        }

        //private static DispatcherTimer CreateTimer(TimeSpan interval, EventHandler handler)
        //{
        //    var timer = new DispatcherTimer();
        //    timer.Interval = interval;
        //    timer.Tick += handler;
        //    timer.Start();

        //    return timer;
        //}

        // Timer callback
        private readonly Rectangle _canvasChildrenLock = new Rectangle();
        public void AddItems()
        {
            lock (_canvasChildrenLock)
            {
                Dispatcher.Invoke((Action)delegate() {
                    var rect = CreateRectangle();
                    rect.Triggers.Add(BeginStoryboardEventTrigger(CreateStoryboard()));
                    MainCanvas.Children.Add(rect); 
                });
            }
        }

        private static EventTrigger BeginStoryboardEventTrigger(Storyboard storyboard)
        {
            var beginStoryboard = new BeginStoryboard {Storyboard = storyboard};

            var eventTrigger = new EventTrigger(LoadedEvent);
            eventTrigger.Actions.Add(beginStoryboard);
            return eventTrigger;
        }

        // Timer callback 
        public void RemoveOffScreenItems()
        {
            lock (_canvasChildrenLock)
            {
                var itemsToRemove = (List<FrameworkElement>)Dispatcher.Invoke((Func<List<FrameworkElement>>)delegate()
                {
                    return (from FrameworkElement element in MainCanvas.Children
                            let topLeft = new Point((double)element.GetValue(Canvas.LeftProperty), (double)element.GetValue(Canvas.TopProperty))
                            where IsOffScreen(topLeft)
                            select element).ToList();
                });

                if (itemsToRemove == null) return;

                foreach (FrameworkElement element in itemsToRemove)
                {
                    Dispatcher.Invoke((Action)delegate() { MainCanvas.Children.Remove(element); });
                }
            }
        }

        private bool IsOffScreen(Point pt)
        {
            return 
                pt.X > MainCanvas.ActualWidth ||
                pt.Y < 0 || pt.Y > MainCanvas.ActualHeight;
        }

        private Rectangle CreateRectangle()
        {
            var rect = new Rectangle
            {
                Width = 100, 
                Height = 100, 
                Fill = _fillBrush
            };

            return rect;
        }

        private const double OffScreenPosition = 100;
        private const double AnimationDuration = 2;
        private Storyboard CreateStoryboard()
        {
            var xAnimation = CreateDoubleAnimationForTranslation();
            xAnimation.From = -OffScreenPosition;
            xAnimation.To = MainCanvas.ActualWidth + OffScreenPosition;
            Storyboard.SetTargetProperty(xAnimation, new PropertyPath(Canvas.LeftProperty));

            var yAnimation = CreateDoubleAnimationForTranslation();
            yAnimation.From = MainCanvas.ActualHeight * Rand.NextDouble();
            yAnimation.To = MainCanvas.ActualHeight * Rand.NextDouble();
            Storyboard.SetTargetProperty(yAnimation, new PropertyPath(Canvas.TopProperty));

            var storyboard = new Storyboard();
            storyboard.Children.Add(xAnimation);
            storyboard.Children.Add(yAnimation);

            storyboard.Freeze();

            return storyboard;
        }

        private DoubleAnimation CreateDoubleAnimationForTranslation()
        {
            var animation = (DoubleAnimation)Dispatcher.Invoke((Func<DoubleAnimation>)delegate()
            {
                return new DoubleAnimation
                {
                    Duration = TimeSpan.FromSeconds(AnimationDuration),
                    EasingFunction = new ShiftedQuadraticEase() { EasingMode = EasingMode.EaseInOut }
                };
            });
            return animation;
        }

        private static readonly Random Rand = new Random(DateTime.Now.Millisecond);
    }
}