Nội dung

45_381304-ch34.qxp Part VIII 7/7/08 2:26 PM Page 846 Advanced Animation Techniques Reversing, inserting, and scaling time The Reverse Time button flips the keys within the selected time block. The Insert Time button lets you insert a section of time anywhere within the current track. To insert time, click and drag to specify the amount of time to insert; all keys beyond the current insertion point slide to accommodate the inserted time. The Scale Time button scales the selected time block. This feature causes all keys to be pushed closer together or farther apart. The scaling takes place around the current frame. Setting ranges The Position Ranges button on the Ranges toolbar enables you to move ranges without moving keys. In this mode, you can move and scale a range bar independently of its keys, ignoring any keys that are out of range. For example, this button, when enabled, lets you remove the first several frames of an animation without moving the keys. The Recouple Ranges button can be used to line up the keys with the range again. The left end of the range aligns with the first key, and the right end aligns with the last key. Editing Curves When an object is moving through the scene, estimating the exact point where its position changes direction can sometimes be difficult. Function curves provide this information by presenting a controller’s value as a function of time. The slope of the function curve shows the value’s rate of change. Steep curves show quick movements. Shallow lines are slow-moving values. Each key is a vertex in the curve. Function curves are visible only in the Curve Editor and the Track Bar layout. Function curves mode lets you edit and work with these curves for complete control over the animation parameters. Figure 34.9 shows the Position curves for a sphere that moves about the scene. FIGURE 34.9 Function curves display keys as square markers along the curve. 846 45_381304-ch34.qxp 7/7/08 2:26 PM Page 847 Working with Function Curves in the Track View Inserting new keys and moving keys Function curves with only two keys have slow in and out tangents, making the animation start slow, speed up, and then slow down. You can add more curvature to the line with the addition of another key. To add another key, click the Add Keys button, and then click the curve where you want to place the key. Keep the total number of keys to a minimum. More keys make editing more difficult. TIP If the curve contains multiple curves, such as a curve for the Position or RGB color values, then a point is added to each curve. The Move Keys button enables you to move individual keys by dragging them. It also includes flyouts for constraining the key movement to a horizontal or vertical direction. Click the Scale Keys button to move the selected keys toward or away from the current time. The keys move only horizontally. Click the Scale Values button to move the selected keys toward or away from the zero value. The keys move only vertically. Tutorial: Animating a monorail As an example of working with function curves, you’ll animate a monorail that moves around its track, changing speeds, and stopping for passengers. To animate the monorail using function curves, follow these steps: 1. Open the Monorail.max file from the Chap 34 directory on the DVD. This file contains a simple monorail setup made from primitives. 2. Click the Play button, and watch the train move around the track. As a default, the Path Constraint’s Percent track has a Linear controller that causes the train to move at a constant speed. To refine the animation, you need to change it. 3. Open the Track View–Curve Editor, and locate the train group’s Percent track. (You can find this track under the Objects ➪ Train ➪ Transform ➪ Path Constraint ➪ Percent menu command.) Click the Assign Controller button or right click and select Assign Controller from the pop-up menu to open the Assign Float Controller dialog box. Select the Bézier Float controller, and click OK. NOTE If the Objects track isn’t visible, open the Filter Tracks dialog box and make sure the Objects option is enabled. 4. Click the Play button. The train starts slowly (represented by the flattish part of the curve), accelerates (the steeper part of the curve), and slows down again (another flattish part). When “reading” function curves, remember that a steep curve produces fast animation, a shallow curve produces slow animation, a horizontal curve produces no movement or value change, and a straight curve produces a constant animation. TIP 5. You need the train to stop for passengers at the station, so click the Add Keys button (or rightclick and choose Add Keys) and add a key somewhere around frame 115 when the train is near the dock. 6. Select the newly created key, and choose the Move Keys Horizontal button from the Move Keys flyout. Hold down the Shift key, and drag right to copy the key to frame 135. The curve is flat, so the train stops at the station. 847 34 45_381304-ch34.qxp Part VIII 7/7/08 2:26 PM Page 848 Advanced Animation Techniques 7. To adjust the actual position where the train stops, choose the Move Keys Vertical button from the Move Keys flyout, select both keys, and move them up or down until the train’s position at the station is correct. Because the default in and out tangent types cause the curve to flatten out at the keys, the train slows as it reaches the station and then starts out slow and picks up speed as it leaves the station. Anyone who has ever ridden on a train knows that stopping and starting are not always smooth operations. Next, you add a few more keys to make the train shudder to a stop and lurch as it starts out again. 8. Click the Add Keys button (or right-click and choose Add Keys), and add keys somewhere around frames 105, 109, 113, 142, and 150. Use Zoom Region to zoom in on the keys where the train pulls into the station to stop. 9. Change the Move Keys Vertical button back to Move Keys by selecting it from the flyout, and move the keys slightly up or down to send the train backward and forward along the path. 10. As you can see, a little movement goes a long way, so the keys need only to be offset a very small amount. Use the Zoom Values button from the Zoom flyout and the Pan button to help in making the small changes to the animation. Figure 34.10 shows the zoomed in view of this section of the curve. FIGURE 34.10 Using Zoom Values to see the stopping position keys 11. Repeat for the keys where the train leaves the station. The train also needs to slow down to look at one of the famous buildings in “Primitive Town,” the Tubular “building” on the far side of the track. 12. Add a couple more keys somewhere around frames 18 and 50. Lower the second of the new keys until the curve is shallower but not horizontal. Again, adjust the train’s position on the track (Percent along the path) by raising or lowering the two new keys. 13. Adjust the Out tangent handle of the very first key and the In tangent handle of the very last key to produce a smooth looping animation. Figure 34.11 shows the final curve after you’ve completed the editing, and Figure 34.12 shows the monorail along its path. 848 45_381304-ch34.qxp 7/7/08 2:26 PM Page 849 Working with Function Curves in the Track View FIGURE 34.11 The finished Percent curve for the train’s position along the path FIGURE 34.12 The monorail and “Primitive Town” 849 34 45_381304-ch34.qxp Part VIII 7/7/08 2:26 PM Page 850 Advanced Animation Techniques Drawing curves If you know what the curve you want is supposed to look like, you can actually draw it in the Key pane with the Draw Curves button enabled. This mode adds a key for every change in the curve. You may want to use the Reduce Keys optimization after drawing a curve. TIP If you make a mistake, you can just draw over the top of the existing curve to make corrections. Figure 34.13 shows a curve that was created with the Draw Curves feature. FIGURE 34.13 Drawing curves results in numerous keys. Reducing keys The Reduce Keys button enables you to optimize the number of keys used in an animation. Certain IK (inverse kinematics) methods and the Dynamics utility calculate keys for every frame in the scene, which can increase your file size greatly. By optimizing with the Reduce Keys button, you can reduce the file size and complexity of your animations. Clicking the Reduce Keys button opens the Reduce Keys dialog box. The threshold value determines how close to the actual position the solution must be to eliminate the key. Figure 34.14 shows the same curve created with the Draw Curves feature after it has been optimized with a Threshold value of 0.5 using the Reduce Keys button. Working with tangents Function curves for the Bézier controller have tangents associated with every key. To view and edit these tangents, click the Show All Tangents button. These tangents are lines that extend from the key point with a handle on each end. By moving these handles, you can alter the curvature of the curve around the key. 850 45_381304-ch34.qxp 7/7/08 2:26 PM Page 851 Working with Function Curves in the Track View You can select the type of tangent from the Key Tangents toolbar. These can be different for the In and Out portion of the curve. You can also select them using the Key dialog box. The default tangent type for all new keys is set using the button to the left of the Key Filters button at the bottom of the Max interface. Using this button, you can quickly select from any of the available tangent types. FIGURE 34.14 The Reduce Keys button optimizes the curve by reducing keys. You open the Key dialog box, shown in Figure 34.15, by selecting a key and clicking the Properties button or by right-clicking the key. It lets you specify two different types of tangent points: Continuous and Discontinuous. Continuous tangents are points with two handles on the same line. The curvature for continuous tangents is always smooth. Discontinuous tangents have any angle between the two handle lines. These tangents form a sharp point. TIP Holding down the Shift key while dragging a handle lets you drag the handle independently of the other handle. FIGURE 34.15 The Key dialog box lets you change the key’s Time, Value, or In and Out tangent curves. The Lock Tangents button lets you change the handles of several keys at the same time. If this button is disabled, adjusting a tangent handle affects only the key of that handle. 851 34 45_381304-ch34.qxp Part VIII 7/7/08 2:26 PM Page 852 Advanced Animation Techniques Tutorial: Animating a flowing river The default auto-tangent types create a function curve that has ease-in and ease-out built into the curve. This causes the animation to start slowly, speed up, and then slow to a stop. While this may be a good starting point for many animations, it won’t work for those that should have a constant speed. This example shows how to create a river with a material animated to a constant speed. To create a flowing river, follow these steps: 1. Open the River.max file from the Chap 34 directory on the DVD. This file contains a river surface made from a loft. The V Offset for the River Water material’s diffuse channel has been animated to simulate flowing water (yes, this river has a checkered past . . .). 2. Click the Play button. The river flow starts out slow, speeds up, and then slows to a stop. NOTE The river flows using a checker texture map. Make sure to select a viewport with textures enabled to see the flowing effect. 3. Open the Track View–Curve Editor, and locate and select the V Offset track for the river’s material. (You can find this track under the Objects ➪ Checkered River ➪ River Water ➪ Maps ➪ Diffuse Color: Map #2 (Checker) ➪ Coordinates ➪ V Offset menu command.) 4. You have two easy options for creating an animation with a constant speed. The first changes the entire controller type; the second changes the individual key’s tangent types. Option 1: Right-click over the V Offset track and choose Assign Controller or choose Assign from Controller on the menu bar to open the Assign Float Controller dialog box. Select Linear Float, and click OK. or Option 2: Select both keys by clicking one key, holding down the Ctrl button, and clicking the other, or by dragging an outline around both keys. Click the Set Tangents to Linear button. Whichever method you use, the line between the two keys is now straight. 5. Click the Play button. The river now flows at a constant speed. 6. To increase the speed of the flow, select Move Keys Vertical from the Move Keys button flyout, and select and move the end key higher in the graph. The river flows faster. Figure 34.16 shows the river as it flows along. Applying out-of-range, ease, and multiplier curves Out-of-range curves define what the curve should do when it is beyond the range of specified keys. For example, you could tell the curve to loop or repeat its previous range of keys. To apply these curves, select a track and click the Parameter Curve Out-of-Range Types button on the Curves toolbar (or select the Out-ofRange menu command from the Controller menu). This opens a dialog box, shown in Figure 34.17, where you can select from the available curve types. 852 45_381304-ch34.qxp 7/7/08 2:26 PM Page 853 Working with Function Curves in the Track View NOTE You can also apply an out-of-range curve to a select range of frames using the Create Out-ofRange Keys utility. This utility is available via the Track View Utilities button. FIGURE 34.16 The Checkered River flows evenly. By clicking the buttons below the types, you can specify a curve for the beginning and end. This Out-ofRange dialog box includes six options:
Constant: Holds the value constant for all out-of-range frames
Cycle: Repeats the track values as soon as the range ends
Loop: Repeats the range values, like the Cycle option, except that the beginning and end points are interpolated to provide a smooth transition
Ping Pong: Repeats the range values in reverse order after the range end is reached
Linear: Projects the range values in a linear manner when out of range
Relative Repeat: Repeats the range values offset by the distance between the start and end values You can apply ease curves (choose Curves ➪ Apply Ease Curve, or press Ctrl+E) to smooth the timing of a function curve. You can apply multiplier curves (Curves ➪ Apply Multiplier Curve, Ctrl+M) to alter the scaling of a function curve. You can use ease and multiplier curves to automatically smooth or scale an animation’s motion. Each of these buttons adds a new track and function curve to the selected controller track. 853 34 45_381304-ch34.qxp Part VIII 7/7/08 2:26 PM Page 854 Advanced Animation Techniques Ease and Multiplier curves add another layer of control on top of the existing animation and allow you to edit the existing animation curves without changing the original animation keys. For example, if you have a standard walk cycle, you can use an ease curve to add a limp to the walk cycle or you can reuse the walk cycle for a taller character by adding a multiplier curve. FIGURE 34.17 The Param Curve Out-of-Range Types dialog box lets you select the type of out-of-range curve to use. NOTE Not all controllers can have an ease or multiplier curve applied. You can delete these tracks and curves using the Delete Ease/Multiplier Curve button. You can also enable or disable these curves with the Enable Ease/Multiplier Curve Toggle button. After you apply an ease or multiplier curve, you can assign the type of curve to use with the Ease Curve Out-of-Range Types button. This button opens the Ease Curve Out-of-Range Types dialog box, which includes the same curve types as the Out-of-Range curves, except for the addition of an Identity curve type. In the Ease Curve Out-of-Range Types dialog box is an Identity option that isn’t present in the Parameter Curve Out-of-Range Types dialog box. The Identity option begins or ends the curve with a linear slope that produces a gradual, constant rate increase. NOTE When editing ranges, you can make the range of a selected track smaller than the range of the whole animation. These tracks then go out of range at some point during the animation. The Ease/Multiplier Curve Outof-Range Types buttons are used to tell the track how to handle its out-of-range time. Tutorial: Animating a wind-up teapot As an example of working with multiplier curves, you’ll create a wind-up teapot that vibrates its way across a surface. To animate the vibrations in the Track View, follow these steps: 1. Open the Wind-up teapot.max file from the Chap 34 directory on the DVD. This file contains a teapot with legs. 2. Click the Play button. 854 45_381304-ch34.qxp 7/7/08 2:26 PM Page 855 Working with Function Curves in the Track View The teapot’s key winds up to about frame 40 and then runs down again as the teapot moves around a bit. To add the random movement and rotation to make the vibrations, you use Noise controllers and Multiplier curves to limit the noise. 3. Open the Track View–Curve Editor, and navigate down to the Wind-up Key’s X Rotation track, located at Objects, Teapot Group, Key, Rotation: Euler XYZ, X Rotation. Take a moment to observe the shape of the curve, shown in Figure 34.18. The key is “wound up” in short spurts and then runs down, slowing until it stops. The vibration, then, should start midway and then taper off as the key runs down. FIGURE 34.18 The rotation of the Wind-up Key object 4. Click the teapot in the viewport to have the curves for its transforms selected and centered in the Track View. When adding the Noise controller, you should assign a List controller first to retain the ability to transform the object independently of the Noise. NOTE Assigning controllers through the Animation menu automatically creates a List controller first. 5. Select the teapot’s Position track, and click the C key to access the Assign Controller dialog box. Choose Position List. Under the Position track are now the X, Y, and Z Position tracks and an Available track. Select the Available track, access the Assign Controller dialog box again, and choose Noise Position. The default controller should remain the Position XYZ controller, so close the List Controller dialog box. Click Play. NOTE Remember that the C keyboard shortcut works only if the Keyboard Shortcut Override Toggle button on the main toolbar is enabled. The teapot vibrates the entire animation. You add a multiplier curve to correct the situation. 855 34