SpeedRatio in VB.NET

Maker QR-Code in VB.NET SpeedRatio

The SpeedRatio property is used to increase or decrease the rate at which time elapses within a timeline. When this value is greater than 1.0 (its default value), the time elapses faster. Likewise, values less than 1.0 cause the timeline to elongate. See Figure 10-5 for a representation of our 10-second timeline sped

up and slowed down. The total length of time for a timeline with this property set (and the other properties set to their defaults) is its Duration multiplied by the SpeedRatio.

Figure 10-5. Illustration of different SpeedRatio values If we put all these properties together (disregarding a RepeatBehavior set to Forever), the total time it takes for an animation is described by the formula shown in Figure 10-6.

Figure 10-6. Formula describing total time span of a timeline Now that you re familiar with how timelines can be represented and manipulated, it s time to see exactly what the animation classes bring to the table beyond the inherited timeline support.

The Storyboard class also inherits from Timeline. This is a special class used as a container for other animations. Its timeline represents a length of time corresponding to the combination of all the timelines in animations stored in the storyboard (if left unspecified) or a length of time that constrains the total animation runtime. The most important aspects of this class are its methods to begin, stop, pause, and resume the animation. These, along with the other methods of the class, are described in Table 10-2. Table 10-2. Methods of System.Windows.Media.Animation.Storyboard

Starts the animation with the first timeline in the storyboard. Returns a ClockState enumeration value. Possible states are Active (the animation is active and is changing in direct relation to its parent timeline), Filling (the animation is active but not changing in direct relation to its parent e.g., it might be paused), and Stopped. Returns a TimeSpan value corresponding to the current time in the storyboard s timeline. Pauses the current storyboard s timeline. Call Resume to unpause the timeline. Resumes the current storyboard s timeline. Accepts a TimeSpan value corresponding to the time in the storyboard s timeline to move to. This can be done while an animation is active or inactive. The seek operation happens on the next clock tick. Same as Seek, but the seek operation happens relative to the last clock tick. Changes the frame of the animation to the end of the storyboard s active period. If AutoReverse is True, the end of the active period is the initial frame of the animation. If RepeatBehavior is Forever, using this method throws an InvalidOperation exception. Stops the animation.

Since the Storyboard class isn t particularly interesting by itself, you ll see it in action when we take a closer look at the animation classes.

The simplest form of animation is generally referred to as from/to/by because of its nature. As explained earlier, three animation classes of Silverlight are applicable to the from/to/by animation type

DoubleAnimation, PointAnimation, and ColorAnimation. The From and To in its name refer to the fact that these animations modify a target property s value starting at the From value and ending at the To value (not taking into account different configurations of the timeline). The By property provides a relative offset controlling where the animation ends, and it is ignored if combined with the To property. Each of these properties can be used by themselves. Table 10-3 describes these properties and how they control the timeline when we use them by themselves. Table 10-3. Usages of From/To/By Properties

This specifies the starting value of the property to animate. The animation stops at the base value of the target property or at the final value of the target property from a previous animation. The target property s value starts at its base value or its final value from a previous animation. It finishes at the value specified in the To property. The target property s value starts at its base value or its final value from a previous animation. The final value of the target property is its initial value added to the value specified in the By property.

The combination of the From/To properties specify the initial (From) and final (To) values of the target Storyboard. The combination of From/By specifies the initial value of the target Storyboard and an offset value used to calculate the target s final value (From + By); however, if you also specify To, it will override the By value.