本文告诉大家如何在 WPF 里，通过 GifBitmapDecoder 调用 WIC 层来解析 GIF 图片，然后采用动画的方式进行播放
使用 WIC 层解析 GIF 图片可以调用系统默认解码器，对 GIF 的支持较好，也能支持很多诡异的格式，而且对这些诡异的图片的行为保持和其他应用相同
这是一个简单的方式，优势在于使用动画播放，十分简单。缺点在于只能支持简单的 GIF 图片格式，也就是每一帧都是全画的 GIF 文件，如果只是范围更新的，那么效果很差
本文的实现可以从本文最后拿到所有代码，下面来告诉大家这是如何做的。 先创建一个继承 FrameworkElement 类型的 GifImage 类，将在这个类里面播放 GIF 图片
定义 GifSource 依赖属性，在依赖属性变更时，进行初始化逻辑
using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Media.Imaging;
class GifImage : FrameworkElement
{
public static readonly DependencyProperty GifSourceProperty = DependencyProperty.Register(
"GifSource", typeof(Uri), typeof(GifImage), new UIPropertyMetadata(default(Uri), GifSourcePropertyChanged));
public Uri GifSource
{
get { return (Uri) GetValue(GifSourceProperty); }
set { SetValue(GifSourceProperty, value); }
}
private static void GifSourcePropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
(sender as GifImage).Initialize();
}
private void Initialize()
{
// 初始化
}
}
在上面的 Initialize 是本文的核心逻辑，将初始化 GIF 的解析
初始化逻辑采用 GifBitmapDecoder 进行解析，代码如下
private void Initialize()
{
_gifDecoder = new GifBitmapDecoder(GifSource, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default);
}
private GifBitmapDecoder _gifDecoder;
可以通过 _gifDecoder.Frames 拿到 GIF 的多个图片，每个图片信息，都可以通过 BitmapMetadata 的 GetQuery 方法获取参数，可以选择的参数有很多，如下
/grctlext控制信息/grctlext/Disposal处置方法，表示如何处理上一张图片，如替换为背景色等/grctlext/TransparencyFlag透明色选项/grctlext/Delay延迟时间，单位是 10 分之一毫秒/grctlext/TransparentColorIndex透明色索引/imgdesc图片描述/imgdesc/Left当前张图片所在的左上坐标和宽高，这里指的是左值/imgdesc/Top当前张图片所在的左上坐标和宽高，这里指的是上值/imgdesc/Width当前张图片所在的左上坐标和宽高，这里指的是宽度/imgdesc/Height当前张图片所在的左上坐标和宽高，这里指的是高度
使用 /grctlext/Delay 获取延时时间，根据延时时间创建动画。动画的方式就是修改当前使用第几张图片
private void Initialize()
{
_gifDecoder = new GifBitmapDecoder(GifSource, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default);
var keyFrames = new Int32KeyFrameCollection();
TimeSpan last = TimeSpan.Zero;
for (int i = 0; i < _gifDecoder.Frames.Count; i++)
{
var gifDecoderFrame = _gifDecoder.Frames[i];
var bitmapMetadata = gifDecoderFrame.Metadata as BitmapMetadata;
var delayTime = bitmapMetadata?.GetQuery("/grctlext/Delay") as ushort?;
var delay = delayTime ?? 10;
if (delay == 0)
{
delay = 10;
}
last += TimeSpan.FromMilliseconds(delay * 10);
keyFrames.Add(new DiscreteInt32KeyFrame(i, KeyTime.FromTimeSpan(last)));
}
_animation = new Int32AnimationUsingKeyFrames()
{
KeyFrames = keyFrames,
RepeatBehavior = RepeatBehavior.Forever,
};
}
private GifBitmapDecoder _gifDecoder;
private Int32AnimationUsingKeyFrames _animation;
添加一个叫播放的函数，调用此函数时，将执行动画
///
/// Starts the animation
///
public void StartAnimation()
{
BeginAnimation(FrameIndexProperty, _animation);
}
public static readonly DependencyProperty FrameIndexProperty =
DependencyProperty.Register("FrameIndex", typeof(int), typeof(GifImage), new FrameworkPropertyMetadata(0, new PropertyChangedCallback(ChangingFrameIndex)));
static void ChangingFrameIndex(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
var gifImage = obj as GifImage;
gifImage.ChangingFrameIndex((int) e.NewValue);
}
private void ChangingFrameIndex(int index)
{
InvalidateVisual();
}
通过动画修改 FrameIndexProperty 从而通过依赖属性修改进入 InvalidateVisual 方法，让框架重新调用 OnRender 方法
protected override void OnRender(DrawingContext drawingContext)
{
var gifDecoderFrame = _gifDecoder.Frames[FrameIndex];
drawingContext.DrawImage(gifDecoderFrame,new Rect(new Size(gifDecoderFrame.PixelWidth, gifDecoderFrame.PixelHeight)));
}
如此即可完成播放
此类型的代码如下
class GifImage : FrameworkElement
{
private bool _isInitialized;
private GifBitmapDecoder _gifDecoder;
private Int32AnimationUsingKeyFrames _animation;
public int FrameIndex
{
get { return (int) GetValue(FrameIndexProperty); }
set { SetValue(FrameIndexProperty, value); }
}
private void Initialize()
{
_gifDecoder = new GifBitmapDecoder(GifSource, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default);
var keyFrames = new Int32KeyFrameCollection();
TimeSpan last = TimeSpan.Zero;
for (int i = 0; i < _gifDecoder.Frames.Count; i++)
{
var gifDecoderFrame = _gifDecoder.Frames[i];
var bitmapMetadata = gifDecoderFrame.Metadata as BitmapMetadata;
var delayTime = bitmapMetadata?.GetQuery("/grctlext/Delay") as ushort?;
var delay = delayTime ?? 10;
if (delay == 0)
{
delay = 10;
}
last += TimeSpan.FromMilliseconds(delay * 10);
keyFrames.Add(new DiscreteInt32KeyFrame(i, KeyTime.FromTimeSpan(last)));
}
_animation = new Int32AnimationUsingKeyFrames()
{
KeyFrames = keyFrames,
RepeatBehavior = RepeatBehavior.Forever,
};
_isInitialized = true;
}
static GifImage()
{
VisibilityProperty.OverrideMetadata(typeof(GifImage),
new FrameworkPropertyMetadata(VisibilityPropertyChanged));
}
private static void VisibilityPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
if ((Visibility) e.NewValue == Visibility.Visible)
{
((GifImage) sender).StartAnimation();
}
else
{
((GifImage) sender).StopAnimation();
}
}
public static readonly DependencyProperty FrameIndexProperty =
DependencyProperty.Register("FrameIndex", typeof(int), typeof(GifImage), new FrameworkPropertyMetadata(0, new PropertyChangedCallback(ChangingFrameIndex)));
static void ChangingFrameIndex(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
var gifImage = obj as GifImage;
gifImage.ChangingFrameIndex((int) e.NewValue);
}
private void ChangingFrameIndex(int index)
{
InvalidateVisual();
}
protected override void OnRender(DrawingContext drawingContext)
{
var gifDecoderFrame = _gifDecoder.Frames[FrameIndex];
drawingContext.DrawImage(gifDecoderFrame,new Rect(new Size(gifDecoderFrame.PixelWidth, gifDecoderFrame.PixelHeight)));
}
///
/// Defines whether the animation starts on it's own
///
public bool AutoStart
{
get { return (bool) GetValue(AutoStartProperty); }
set { SetValue(AutoStartProperty, value); }
}
public static readonly DependencyProperty AutoStartProperty =
DependencyProperty.Register("AutoStart", typeof(bool), typeof(GifImage), new UIPropertyMetadata(false, AutoStartPropertyChanged));
private static void AutoStartPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
if ((bool) e.NewValue)
(sender as GifImage).StartAnimation();
}
public static readonly DependencyProperty GifSourceProperty = DependencyProperty.Register(
"GifSource", typeof(Uri), typeof(GifImage), new UIPropertyMetadata(default(Uri), GifSourcePropertyChanged));
public Uri GifSource
{
get { return (Uri) GetValue(GifSourceProperty); }
set { SetValue(GifSourceProperty, value); }
}
private static void GifSourcePropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
(sender as GifImage).Initialize();
}
///
/// Starts the animation
///
public void StartAnimation()
{
if (!_isInitialized)
this.Initialize();
BeginAnimation(FrameIndexProperty, _animation);
}
///
/// Stops the animation
///
public void StopAnimation()
{
BeginAnimation(FrameIndexProperty, null);
}
}
除此之外的其他播放 GIF 方法，请看：
更多请看
可以通过如下方式获取本文的源代码，先创建一个空文件夹，接着使用命令行 cd 命令进入此空文件夹，在命令行里面输入以下代码，即可获取到本文的代码
git init
git remote add origin https://gitee.com/lindexi/lindexi_gd.git
git pull origin e11f2ea15fd5107fac4bd4523580587ce7febd56
以上使用的是 gitee 的源，如果 gitee 不能访问，请替换为 github 的源
git remote remove origin
git remote add origin https://github.com/lindexi/lindexi_gd.git
获取代码之后，进入 CairjawworalhulalGeacharkucoha 文件夹
Original: https://www.cnblogs.com/lindexi/p/16734400.html
Author: lindexi
Title: WPF 通过 GifBitmapDecoder 调用 WIC 解析 Gif 和进行动画播放的简单方法
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