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Lesson 2. Ballet Special Bumper > Creating a motion path

Creating a motion path

To make the letters dance off of the screen, you'll start by creating a motion path. You define the motion path by setting Position keyframes. After creating the initial motion path, you can edit it in the Composition window.

  1. In the Time Layout window, set the current time to 07:25, and make sure all the letter layers are selected.

  2. Press the P key to see the Position property for all the letters, and then press Alt+Shift+P (Windows) or Option+P (Mac OS) to set an initial Position keyframe for all the letter layers.

  3. Move the current-time marker to 08:03, and press Ctrl+Shift+A (Windows) or Command+Shift+A (Mac OS) to deselect all layers. Select the T layer in the Composition window, and then drag the letter t slightly to the right. A second Position keyframe appears in the Time Layout window.

    Figure .

  4. Set the current time to 08:10, and then drag the T layer slightly up and to the right. Another keyframe is created.

    Figure .

  5. Set the current time to 08:20, and then drag the T layer down and to the right.

    Figure .

  6. Set the current time to 09:00, and then drag the T layer off the top part of the frame.

    Figure .

  7. To set the work area in order to preview the motion so far, move the current-time marker to 07:15, and then press the B key to set the beginning of the work area. Next, move the current-time marker to 09:10, and press the N key to set the end of the work area.

  8. Preview the motion using a Wireframe preview (an outline of the alpha channels playing back motion at real time) by pressing Opt+0 (on the numeric keypad).

    Because the letter was applied to a rectangular solid, you will not see the letter outline, but rather the rectangular outline of the solid layer.

  9. Press any key to stop the preview.

Using the shuttle control

If you were to use the play button on the Time Controls palette (or the spacebar) to play the composition, the playback would be slow. You can use the shuttle control in the Time Controls palette to see faster playback, and to see the shapes of the letters.

  1. Set the current time to 07:15.

  2. In the Time Controls palette, drag the shuttle control slightly to the right.

    Figure . A. Jog control B. Shuttle control C. Time indicator

The shuttle control shuttles through the composition starting from the current-time marker. The farther you drag the control from the center, the faster the content of the Composition window plays. You can play the composition both forward and backward by dragging to the right or to the left, respectively. You may have to experiment with how far to drag the control to see a helpful preview. The shuttle control does not loop the playback, so you will need to set the current-time marker to the beginning to view the frames again.

As you drag the shuttle control back and forth to preview your composition, notice the time indicator just below the jog control. The time indicator here shows which frame you are currently viewing relative to the beginning and end of the composition, and updates to reflect this as you shuttle through a composition. You can also drag the time indicator along the jog control to move quickly through the composition. To move slowly, you can drag inside the jog control.

About direction lines and direction handles

Before you draw and modify curved lines with the pen tool, it is important to know about two elements that are associated with anchor points on curves. On curved segments, each selected anchor point displays one or two direction lines (also called tangents), ending in direction handles (also called Bezier direction handles). The positions of direction lines and handles determine the size and shape of a curved segment. Moving these elements reshapes the curves in a path.

Figure . A. Curved segment B. Direction handle C. Anchor point D. Direction line or tangent

The direction lines are always tangent to (touching) the curve at the anchor points. The slope of each direction line determines the slope of the curve, and the length of each direction line determines the height, or depth, of the curve.

Figure . Moving direction lines changes the slope of the curve.

Figure . Drag in the opposite direction to create a smooth curve. Drag in the same direction to create "S" curve.

Editing the motion path

With the T layer still selected, you can examine the motion path for the T layer in the Composition window. Each X represents a keyframe, and each dot marks the position of the layer at each frame. The spacing of the dots indicates the speed of the layer. Notice that the dots are closer together between keyframes that are closer together in time, and farther apart where keyframes are farther apart. The closer together the dots are, the slower the layer is moving at that point. The farther apart the dots are, the faster the layer is moving.

You can edit the Position keyframes by editing the motion path.

  1. In the Time Layout window, make sure the Position property is displayed for the T layer, set the current time to 8:10, and then take note of the position coordinates.

  2. In the Composition window, drag the layer up and slightly to the left. The position coordinates for this keyframe change.

    You don't need to move the current-time marker to edit the position keyframes.

    Figure .

  3. In the Composition window, select the X that represents the next keyframe, and move it up and slightly to the right.

    Figure .

  4. Select the X that is above the top of the frame, and move it to the left.

    Figure .

    You can use the pen tool in the toolbox to edit and add keyframes to the motion path. Editing with the pen tool is similar to the way you edit paths in Adobe Illustrator.

  5. Position the current-time marker at 08:20, and in the toolbox, select the pen tool. In the Composition window, position the pen over a dot on the motion path, as shown in the illustration below, so that a plus icon appears next to the pen tool icon. (This is the add control point tool.) Click the motion path. A new keyframe appears between 8:20 and 9:00.

    Figure .

    In addition to the new keyframe symbol, two layer tangentsor direction handles appear. The default spatial interpolation method is continuous Bezier interpolation. Bezier interpolation provides the most precise control over the motion path. You use the handles to control the arc of the curve, just as you do with the pen tool in Adobe Illustrator and Adobe Photoshop.

  6. Select the selection tool in the toolbox, and then drag the new keyframe to the right.

    Figure .

    Before completing your adjustments to the motion path, you will explore some of the motion path controls that you have available by selecting options in the Composition window menu in the upper right corner of the Composition window.

    Figure .

  7. In the Composition window, choose Layer Keyframes from the Composition window menu; the keyframe symbols disappear. Choose the command again to turn the keyframes back on.

  8. Choose Layer Paths from the Composition window menu; the layer path disappears. Choose the command again to turn the path back on.

    The Layer Tangents option shows the direction handles of a Bezier curve. You can drag these handles to modify the path.

  9. Leave the Layer Tangents command turned on (displaying a checkmark), and then click the newest keyframe that you created. Drag the direction handles to change the arc of the curve.

    Figure .

  10. Choose Layer Handles from the Composition window menu. The handles for the selected layer disappear. Hiding the selection handles makes it easier to work with the direction handles.

  11. Select each keyframe one at a time, except the first two, and use the direction handle to alter the curve until you get a path that you like. When you are finished, choose Layer Handles from the Composition window menu again to turn layer handles back on.

    Figure .

  12. Press Alt+0 (Windows) or Option+0 (Mac OS) on your numeric keypad to preview the motion.

  13. Set the current time to 07:25, and then use the jog control to see the t move along the motion path frame by frame. Save the project.

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