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Chapter 4. Animating Sprites > Adjusting Motion

Adjusting Motion

After you tween a path for a sprite to follow, you can make numerous adjustments in the motion of the sprite (such as adding acceleration) to create a more realistic animation.

The quickest and most convenient way to adjust the path of a sprite is to use Sprite Overlay view, which allows you to see the complete path of the sprite—and its keyframes—on the stage.

To view and adjust the path of a sprite on the stage:

1.
In the score, select the sprite whose path you want to view or adjust.

2.
Choose View > Sprite Overlay > Show Paths.

The complete path of the sprite appears on the stage (Figure 4.20). Keyframes within the path are symbolized by small circles; regular frames, by small dots.

Figure 4.20. The path of the sprite is shown on the stage.


3.
Drag any keyframe symbol in the overlay to a new position (Figure 4.21).

Figure 4.21. You can adjust the path by dragging any keyframe.


The sprite's path adjusts immediately.

Tip

When you select an entire sprite in the score and then change its position on the stage, you move the entire sprite throughout all its frames relative to the new position (as opposed to adjusting the position in a single keyframe).


When a sprite uses three or more keyframes, you can make the path between them follow a curve rather than a straight line.

To add curvature to a sprite's tweened path:

1.
In the score, select a sprite whose path needs adjustment.

2.
Choose Modify > Sprite > Tweening.

3.
In the Sprite Tweening dialog box, drag the Curvature slider to adjust how much curvature is in the sprite's path.

You can preview the adjusted path on the left side of the Sprite Tweening dialog box (Figure 4.22).

Figure 4.22. Preview the tweening path.


Drag the slider to the Linear end to move the sprite between keyframes in straight lines (Figure 4.23).

Figure 4.23. Linear path settings produce straight-line motion.


Drag to the Normal end to give the sprite's path moderate curvature.

Drag to the Extreme end for maximum curvature in the path between keyframes (Figure 4.24).

Figure 4.24. Extreme curvature produces a curved path for the sprite.


When you want a sprite to move in a circular path, use this method.

To create a circular path for a sprite:

1.
Place a cast member in the score to create a sprite.

2.
Create a total of three keyframes within the sprite (Figure 4.25).

Figure 4.25. Create three keyframes.


You can use the start frame, but don't create a keyframe at the end frame.

3.
Choose View > Sprite Overlay > Show Paths to turn on the display of sprite paths.

4.
On the stage, position the sprite's keyframes as corners of an equilateral triangle (Figure 4.26).

Figure 4.26. Position the sprite's keyframes in a triangle.


5.
Select the sprite in the score and choose Modify > Sprite > Tweening.

The Sprite Tweening dialog box opens.

6.
Check the Continuous at Endpoints checkbox.

That option makes the path a closed triangular path (Figure 4.27).

Figure 4.27. The closed path still looks triangular.


7.
Drag the Curvature slider to the right to make the sprite's path resemble a circle.

Use the path preview on the left side of the Sprite Tweening box as a guide (Figure 4.28).

Figure 4.28. The path preview and the circular path after adjustment.


8.
Click OK.

9.
Fine-tune the circular path, if necessary, by dragging the keyframes (represented by circles) within the Sprite Overlay on the stage.

When you tween a sprite along any path, you can make it change speed at the beginning or end to add a touch of realism.

To accelerate or decelerate a sprite along its path:

1.
Set up keyframes and tween your sprite along a path.

2.
Select the sprite in the score.

3.
Choose Modify > Sprite > Tweening.

4.
In the Sprite Tweening dialog box, drag the Ease-In and Ease-Out slider bars to control the sprite's acceleration along its path.

Ease-In controls the beginning speed. High percentages make the sprite take a longer time to reach top speed along the path. Ease-Out controls the ending speed. High percentages for Ease-Out make the sprite take a long time to slow down (Figure 4.29).

Figure 4.29. Drag the Ease-In and Ease-Out slider bars in the Sprite Tweening dialog box to control a sprite's acceleration and deceleration.


When a sprite follows a tweened path, it may move smoothly and slowly between certain keyframes but then suddenly speed up and move abruptly between other keyframes. These abrupt speed changes occur when too few frames lie between keyframes. Use the following to smooth abrupt speed changes.

To smooth the speed changes of a moving sprite:

1.
Select the sprite whose speed changes you want to smooth.

2.
Choose Modify > Sprite > Tweening.

3.
In the Sprite Tweening dialog box, check the Smooth Changes speed option (Figure 4.30).

Figure 4.30. Click Smooth Changes in the Sprite Tweening dialog box to make speed changes more gradual.


Sharp Changes is the default selection.

4.
Click OK.

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