Furrball Animation

Jerry Yee

3/14/2005

CMPS 161

This application animates Furrball, a cartoon cat in the Warner Brother’s Tiny Toon Adventures cartoon series. The character is created in 3D and stands in a simple 3D football field. The primary focus of this project is animating Furrball with hair - making it walk and animating the hair.

User Guide

To move Furrball, set the focus to the render window by clicking inside the render window. Then use the following keyboard keys:

To turn to Furrball’s left – press the left arrow button

To turn to Furrball’s right – press the right arrow button

To move Furrball forward – press the up arrow button

To move Furrball backward – press the down arrow button

In the application window, there are sliders to change the camera position. The camera is always aimed at Furrball’s head. And the camera’s view-up vector is always up (the y-axis). To move the camera:

To the left - move the camera’s x slider down

To the right – move the camera’s x slider up

Up towards an overhead view – move the camera’s y slider up

Down towards a perpendicular view – move the camera’s y slider down

Closer to Furrball – move the camera’s z slider up

Farther from Furrball – move the camera’s z slier down

There are also sliders to modify Furrball’s hair count and walking speed:

To decrease the number of hairs – move the density slider down

To increase the number of hairs – move the density slider up

To decrease the walking speed – move the speed slider down

To increase the walking speed – move the speed slider up

Implementation

Furrball is created and animated using hierarchical animation. It is rendered using separate coordinate and polygon files for each limb: head, body, arm, hand (includes lower arm), leg, foot (includes lower leg). The right and left arms are generated from the same files, as are the hands, legs, and feet. The body is the main limb. The head, arms, and legs are children of the body. The hands and feet are grandchildren of the body.

Walking

Forward kinematics is used to rotate and translate the limbs as Furrball walks. The leg has two degrees of freedom. It rotates about the y-axis and bends about the z-axis. The feet has one degree of freedom. It bends about the z-axis. The arm has one degree of freedom. It rotates about the z-axis. The hand has one degree of freedom. It bends about the x-axis.

There are 5 key frames in the walking sequence. The degrees of rotation are interpolated for each key frame. For example if the total rotation between the current and next key frame is 90 degrees and parameter t is some real number between 0 and 1, then the rotation at some t is (90 * t). Furrball is at rest in key frame 1.

In key frame 2, Furrball’s body goes up, right leg goes forward as the left leg goes backward a little. The opposing arms move similarly. And the head bobs to the left.

In key frame 3, Furrball’s body goes down, the head , legs, and arms go back to the resting position.

In key frame 4, Furrball’s body goes up, left leg goes forward as the right leg goes backward a little. The opposing arms move similarly. And the head bobs to the right.

In key frame 5, Furrball’s body goes down, the head , legs, and arms go back to the resting position.

Hair Animation

Hair covers most of Furrball’s body, except the eyes, nose, hands, and feet. The hair is randomly generated using particle simulation and line integration. For each hair, a particle is projected from a random position on Furrball (a polygon). The initial velocity is in the same direction as the polygon’s normal vector. The velocity changes as a result of gravity and Furrball’s bouncing and head bobbing as it walks. The particle’s position is taken at 8 consecutive moments and they are connected by a line to form a single strand of hair.

Below is a close-up image of the hair in Furrball’s resting frame. Note that only gravitational forces are applied to the hair in this state.

Below is a close-up image of the hair as Furrball bounces up. Note that the hair has gone down a little from the upward movement.

Below is a close-up image of the hair as Furrball bounces down. Note that the hair has gone up a little from the downward movement.