Animates from the Point value of the previous key frame to the Value of the current key frame, by using discrete values.
A key frame defines a segment of the PointAnimationUsingKeyFrames object to which it belongs. Each key frame has a target Value and KeyTime. The KeyTime specifies the time at which the key frame's Value should be reached. The animation progresses from the target value of the previous key frame to the target value of the current key frame. The animation starts when the previous key frame ends, and the animation ends when the key time of the current key frame is reached.
Discrete key frames, such as DiscretePointKeyFrame, create sudden jumps between values (no interpolation). The animated property does not change until the key frame's key time is reached, at which point the animated property suddenly changes to the target value.
The following example moves an ellipse along a triangular path. The example uses a PointAnimationUsingKeyFrames object to animate the Center property of an EllipseGeometry object. This animation uses three key frames in the following manner:
During the first half second, a LinearPointKeyFrame object moves the ellipse along a path at a steady rate from its starting position. Linear key frames, such as LinearPointKeyFrame, create a smooth linear interpolation between values.
During the end of the next half second, a DiscretePointKeyFrame object suddenly move the ellipse along the path to the next position. Discrete key frames, such as DiscretePointKeyFrame, create sudden jumps between values.
During the final two seconds, a SplinePointKeyFrame object moves the ellipse back to its starting position. Spline key frames, such as SplinePointKeyFrame, create a variable transition between values according to the values of the KeySpline property. KeySpline provides a nonlinear way to alter the relationship of time versus value during the animation duration. In particular, the relationship can be a curve that would be difficult to produce with individual key frames. In this example, the animation begins slowly and speeds up exponentially toward the end of the time segment.
<Canvas xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Width="400" Height="300"> <Path Fill="Blue"> <Path.Data> <!-- Describes an ellipse. --> <EllipseGeometry x:Name="MyAnimatedEllipseGeometry" Center="200,100" RadiusX="15" RadiusY="15" /> </Path.Data> <Path.Triggers> <EventTrigger RoutedEvent="Path.Loaded"> <BeginStoryboard> <Storyboard> <!-- Animating the Center property uses three key frames, which animate the ellipse along a triangular path. --> <PointAnimationUsingKeyFrames Storyboard.TargetProperty="Center" Storyboard.TargetName="MyAnimatedEllipseGeometry" Duration="0:0:5" RepeatBehavior="Forever"> <!-- Over the first half second, using a LinearPointKeyFrame, the ellipse moves steadily from its starting position along the first line of the triangular path. --> <LinearPointKeyFrame KeyTime="0:0:0.5" Value="100,300" /> <!-- Using a DiscretePointKeyFrame, the ellipse suddenly changes position after the first second of the animation. --> <DiscretePointKeyFrame KeyTime="0:0:1" Value="400,300" /> <!-- Using a SplinePointKeyFrame, the ellipse moves back to its starting position. It moves slowly at first and then speeds up. This key frame takes 2 seconds to complete. --> <SplinePointKeyFrame KeySpline="0.6,0.0 0.9,0.00" KeyTime="0:0:3" Value="200,100" /> </PointAnimationUsingKeyFrames> </Storyboard> </BeginStoryboard> </EventTrigger> </Path.Triggers> </Path> </Canvas>