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Cómo animar la posición o el color de un punto de gradiente

En este ejemplo se muestra cómo animar el Color y Offset de los objetos GradientStop.

Ejemplo

En el ejemplo siguiente se animan tres paradas de degradado dentro de un LinearGradientBrush. En el ejemplo se usan tres animaciones, cada una de las cuales anima una parada de degradado diferente:

  • La primera animación, un DoubleAnimation, anima el primer punto de degradado Offset de 0,0 a 1,0 y luego de vuelta a 0,0. Como resultado, el primer color del degradado cambia del lado izquierdo al lado derecho del rectángulo y, a continuación, vuelve al lado izquierdo.

  • La segunda animación, ColorAnimation, anima el segundo punto de degradado Color de Purple a Yellow y luego de vuelta a Purple. Como resultado, el color central del degradado cambia de púrpura a amarillo y de vuelta a púrpura.

  • La tercera animación, otra ColorAnimation, anima la opacidad del tercer punto del degradado Color hasta -1 y luego regresa. Como resultado, el tercer color del degradado desaparece y, a continuación, vuelve a ser opaco.

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;
        }
    }
}


Imports System.Windows
Imports System.Windows.Controls
Imports System.Windows.Input
Imports System.Windows.Media
Imports System.Windows.Media.Animation
Imports System.Windows.Shapes

Namespace BrushesIntroduction
    Public Class GradientStopAnimationExample
        Inherits Page
        Public Sub New()
            Title = "GradientStop Animation Example"
            Background = Brushes.White

            ' Create a NameScope for the page so that
            ' Storyboards can be used.
            NameScope.SetNameScope(Me, New NameScope())

            ' Create a rectangle. This rectangle will
            ' be painted with a gradient.
            Dim aRectangle As New Rectangle()
            aRectangle.Width = 200
            aRectangle.Height = 100
            aRectangle.Stroke = Brushes.Black
            aRectangle.StrokeThickness = 1

            ' Create a LinearGradientBrush to paint
            ' the rectangle's fill.
            Dim gradientBrush As New LinearGradientBrush()

            ' Create gradient stops for the brush.
            Dim stop1 As New GradientStop(Colors.MediumBlue, 0.0)
            Dim stop2 As New GradientStop(Colors.Purple, 0.5)
            Dim stop3 As 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.
            Me.RegisterName("GradientStop1", stop1)
            Me.RegisterName("GradientStop2", stop2)
            Me.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.
            '
            Dim offsetAnimation As 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.
            '
            Dim gradientStopColorAnimation As 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.
            '
            Dim opacityAnimation As 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.
            Dim gradientStopAnimationStoryboard As 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.
            AddHandler aRectangle.MouseLeftButtonDown, Sub(sender As Object, e As MouseButtonEventArgs) gradientStopAnimationStoryboard.Begin(Me)

            Dim mainPanel As New StackPanel()
            mainPanel.Margin = New Thickness(10)
            mainPanel.Children.Add(aRectangle)
            Content = mainPanel
        End Sub
    End Class
End Namespace

<Page  
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://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>

Aunque en este ejemplo se usa un LinearGradientBrush, el proceso es el mismo para animar objetos GradientStop dentro de un RadialGradientBrush.

Para obtener ejemplos adicionales, consulte el Ejemplo de Pinceles.

Consulte también