3ds Max 2012 Bible - Kelly L. Murdock [468]
If you press the Escape key while in Live mode, a dialog box appears, giving you the option to Freeze, Stop, or Continue. If you click the Freeze button, then the hair stays in its current position.
The Precomputed mode is available only after you've specified a Stat File name. This mode lets you save the hair motions into a separate stat file.
Setting properties
Only a few properties need to be defined to enable hair dynamics. In the Dynamics rollout, you find values for Gravity, Stiffness, Root Hold, and Dampen. These properties control how the hair behaves in response to the environment forces. The Gravity value can be negative if you want the hair to rise instead of fall. You can simulate space environments by setting the gravity to 0. The Stiffness value eliminates all dynamic movement if set to 1.0. If you want the hair to move only slightly as the object moves, then a Stiffness value close to 1.0 should work. The Root Hold value is like stiffness but applies only to the root. The Dampen value causes motions to die out quickly.
All dynamic properties except Gravity can be controlled using a grayscale map, using the small button to the right of the value field.
Enabling collisions
The first type of dynamic force to address is to enable collisions between the hair and the other scene objects. To enable collisions between the growth object and its hair, simply enable the Use Growth Object option. This option is only enabled when Sphere or Polygon Collisions are enabled first. In addition to the growth object, other scene objects can be added to the list with which the hair will collide. To add other objects, click the Add button and pick the object to add in the viewport. Each collision object can use either a boundary Sphere to define its collision volume or a Polygon, which bases collisions on the actual surface geometry. The latter takes longer to compute, but it's more accurate.
Enabling forces
In addition to the ubiquitous gravity, you can enable collisions between the hairs and the growth object and any other scene objects. To add another scene object to the collision calculations, click the Add button and select the new collision object. The External Forces list lets you add Space Warps for additional forces such as Wind.
Running a simulation
The Precomputed mode lets you save the hair dynamics to a separate stat file. If you want to capture the dynamic simulation, you first must specify a stat file by clicking the button to the right of the Stat File section. With a stat file specified, click the Run button in the Simulation section to calculate the dynamic solution. The Start and End fields let you enter the range for the simulation. A separate stat file is generated for every frame of the animation.
If you enable the Precomputed mode option before you render, then the stat file is read and used during the rendering process. You can delete all stat files quickly with the scarily named Delete all files button.
Tutorial: Simulating hair dynamics
Dynamic hair moves and flows around the other objects in the scene that are animated. As an example of this, you'll move a female character's head back and forth and simulate how the hair moves. I selected the Mohawk hairstyle because I'm hip and cool, a real rebel. Actually, the Mohawk is a simple style and gives you a chance to play with the Stiffness property.
To simulate the dynamics of a hair system, follow these steps:
1. Open the Female head with mohawk.max file from the Chap 44 directory on the CD.
This file includes the head from a female character model created by Zygote Media. The hair modifier already has been added to this character and styled.
2. Click the Auto Key button, drag the Time Slider to frame 5, and move the character to the right in the Top viewport. Then drag the Time Slider to frame 10, and move the character back to the left. This simple motion should be enough to bend the hair over. Then disable the Auto Key mode.
3. With the head selected, open the Dynamics rollout