如何:对渐变停止点的位置或颜色进行动画处理

更新:2007 年 11 月

本示例演示如何对 GradientStop 对象的 ColorOffset 进行动画处理。

示例

下面的示例对 LinearGradientBrush 中的三个渐变停止点进行动画处理。本示例使用三个动画,每个动画都对一个不同的渐变停止点进行动画处理:

  • 第一动画(即 DoubleAnimation)对第一个渐变停止点的 Offset 进行动画处理,使其从 0.0 到 1.0 然后又回到 0.0。因此,该渐变中的第一种颜色会从矩形的左侧移动到右侧,然后又移动回到左侧。

  • 第二个动画(即 ColorAnimation)对第二个渐变停止点的 Color 进行动画处理,使从 Purple 变为 Yellow 然后又变回 Purple。因此,该渐变中位于中间的颜色会从紫色改为黄色,之后又改回紫色。

  • 第三个动画(即另一个 ColorAnimation)以 -1 为增量对第三个渐变停止点的 Color 的不透明度进行动画处理,之后又进行相反的处理。因此,该渐变中的第三种颜色会褪掉,之后再次变为不透明。

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace BrushesIntroduction
{
    public class GradientStopAnimationExample : Page
    {
        public GradientStopAnimationExample()
        {
            Title = "GradientStop Animation Example";
            Background = Brushes.White;

            // Create a NameScope for the page so that
            // Storyboards can be used.
            NameScope.SetNameScope(this, new NameScope());

            // Create a rectangle. This rectangle will
            // be painted with a gradient.
            Rectangle aRectangle = new Rectangle();
            aRectangle.Width = 200;
            aRectangle.Height = 100;
            aRectangle.Stroke = Brushes.Black;
            aRectangle.StrokeThickness = 1;

            // Create a LinearGradientBrush to paint
            // the rectangle's fill.
            LinearGradientBrush gradientBrush = new LinearGradientBrush();

            // Create gradient stops for the brush.
            GradientStop stop1 = new GradientStop(Colors.MediumBlue, 0.0);
            GradientStop stop2 = new GradientStop(Colors.Purple, 0.5);
            GradientStop stop3 = new GradientStop(Colors.Red, 1.0);

            // Register a name for each gradient stop with the
            // page so that they can be animated by a storyboard.
            this.RegisterName("GradientStop1", stop1);
            this.RegisterName("GradientStop2", stop2);
            this.RegisterName("GradientStop3", stop3);

            // Add the stops to the brush.
            gradientBrush.GradientStops.Add(stop1);
            gradientBrush.GradientStops.Add(stop2);
            gradientBrush.GradientStops.Add(stop3);

            // Apply the brush to the rectangle.
            aRectangle.Fill = gradientBrush;

            //
            // Animate the first gradient stop's offset from
            // 0.0 to 1.0 and then back to 0.0.
            //
            DoubleAnimation offsetAnimation = new DoubleAnimation();
            offsetAnimation.From = 0.0;
            offsetAnimation.To = 1.0;
            offsetAnimation.Duration = TimeSpan.FromSeconds(1.5);
            offsetAnimation.AutoReverse = true;
            Storyboard.SetTargetName(offsetAnimation, "GradientStop1");
            Storyboard.SetTargetProperty(offsetAnimation, 
                new PropertyPath(GradientStop.OffsetProperty));

            //
            // Animate the second gradient stop's color from
            // Purple to Yellow and then back to Purple.
            //
            ColorAnimation gradientStopColorAnimation = new ColorAnimation();
            gradientStopColorAnimation.From = Colors.Purple;
            gradientStopColorAnimation.To = Colors.Yellow;
            gradientStopColorAnimation.Duration = TimeSpan.FromSeconds(1.5);
            gradientStopColorAnimation.AutoReverse = true;
            Storyboard.SetTargetName(gradientStopColorAnimation, "GradientStop2");
            Storyboard.SetTargetProperty(gradientStopColorAnimation,
                new PropertyPath(GradientStop.ColorProperty));

            // Set the animation to begin after the first animation
            // ends.
            gradientStopColorAnimation.BeginTime = TimeSpan.FromSeconds(3);

            //
            // Animate the third gradient stop's color so
            // that it becomes transparent.
            //
            ColorAnimation opacityAnimation = new ColorAnimation();

            // Reduces the target color's alpha value by 1, 
            // making the color transparent.
            opacityAnimation.By = Color.FromScRgb(-1.0F, 0F, 0F, 0F);
            opacityAnimation.Duration = TimeSpan.FromSeconds(1.5);
            opacityAnimation.AutoReverse = true;
            Storyboard.SetTargetName(opacityAnimation, "GradientStop3");
            Storyboard.SetTargetProperty(opacityAnimation,
                new PropertyPath(GradientStop.ColorProperty));

            // Set the animation to begin after the first two
            // animations have ended. 
            opacityAnimation.BeginTime = TimeSpan.FromSeconds(6);

            // Create a Storyboard to apply the animations.
            Storyboard gradientStopAnimationStoryboard = new Storyboard();
            gradientStopAnimationStoryboard.Children.Add(offsetAnimation);
            gradientStopAnimationStoryboard.Children.Add(gradientStopColorAnimation);
            gradientStopAnimationStoryboard.Children.Add(opacityAnimation);

            // Begin the storyboard when the left mouse button is
            // pressed over the rectangle.
            aRectangle.MouseLeftButtonDown += delegate(object sender, MouseButtonEventArgs e)
            {
                gradientStopAnimationStoryboard.Begin(this);
            };

            StackPanel mainPanel = new StackPanel();
            mainPanel.Margin = new Thickness(10);
            mainPanel.Children.Add(aRectangle);
            Content = mainPanel;
        }
    }
}
<Page  
  xmlns="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="https://schemas.microsoft.com/winfx/2006/xaml"
  Title="GradientStop Animation Example"
  Background="White">
  <StackPanel Margin="10">

    <Rectangle
      Width="200" 
      Height="100" 
      Stroke="Black" StrokeThickness="1">
      <Rectangle.Fill>
        <LinearGradientBrush>
          <GradientStop x:Name="GradientStop1" Color="MediumBlue" Offset="0.0" />
          <GradientStop x:Name="GradientStop2" Color="Purple" Offset="0.5" />
          <GradientStop x:Name="GradientStop3" Color="Red" Offset="1.0" />
        </LinearGradientBrush>
      </Rectangle.Fill>
      <Rectangle.Triggers>
        <EventTrigger RoutedEvent="Rectangle.MouseLeftButtonDown">
          <BeginStoryboard>
            <Storyboard>
              <DoubleAnimation 
                Storyboard.TargetName="GradientStop1"
                Storyboard.TargetProperty="Offset"
                From="0.0" To="1.0" Duration="0:0:1.5"
                AutoReverse="True" />
              <ColorAnimation 
                Storyboard.TargetName="GradientStop2"
                Storyboard.TargetProperty="Color"
                From="Purple" To="Yellow" 
                Duration="0:0:1.5"
                AutoReverse="True"
                BeginTime="0:0:3" />
              <ColorAnimation 
                Storyboard.TargetName="GradientStop3"
                Storyboard.TargetProperty="Color" 
                Duration="0:0:1.5" 
                AutoReverse="True"
                BeginTime="0:0:6">
                <ColorAnimation.By>
                  <Color ScA="-1" ScR="0" ScB="0" ScG="0" />
                </ColorAnimation.By>
              </ColorAnimation>
            </Storyboard>
          </BeginStoryboard>
        </EventTrigger>
      </Rectangle.Triggers>
    </Rectangle>

  </StackPanel>
</Page>

尽管本示例使用 LinearGradientBrush,但是其过程与对 RadialGradientBrush 中的 GradientStop 对象进行动画处理相同。

有关其他示例,请参见Brush 示例

请参见

概念

动画概述

演示图板概述

参考

GradientStop