In a computerized image rendering system, wherein images are generated based on a geometric model of simulated or actual objects such that the images, when displayed on a display device, represent a view of the simulated or actual objects forming a scene, the geometric models being in an electronically readable form readable by the image rendering system and the images generated being in an electronic form readable by a display system, further wherein the images represent a sequence of movements from frame to frame of the simulated or actual objects, a method of generating the images comprising:
- tracking, for a character to be rendered and comprising one or more simulated or actual objects organized as a plurality of body parts movable relative to other body parts, whether the character's movement is to be ballistic or non-ballistic;
- when movement of the character is non-ballistic, computing forces in a non-ballistic mode characterized by external forces being predominant and applying those external forces to the plurality of body parts, thereby imbuing the character with non-ballistic motion;
- detecting when movement of the character changes from non-ballistic to ballistic, wherein detecting when movement of the character changes from non-ballistic to ballistic includes:
- performing a balance check on the character, the balance check comprising:
- a) determining an estimated center of mass for the character by averaging together a pelvis center-of-mass position and a torso center of mass-position of the character;
- b) constructing a support circle based upon positions of character's lower extremities;
- c) determining a distance that the estimated center of mass is outside of the support circle;
- d) comparing the distance that the estimated center of mass is outside of the support circle to a predetermined threshold;
- and
- e) signaling a change to ballistic motion, if the distance that the estimated center of mass is outside of the support circle exceeds the predetermined threshold;
- when the movement of the character changes from non-ballistic motion to ballistic motion:
- a) computing forces in a ballistic mode characterized by spring-like internal forces being predominant;
- and
- b) applying the forces to the plurality of body parts, thereby imbuing the character with ballistic motion;
- calculating positions of each of the plurality of body parts in the ballistic mode for a current frame from at least the spring-like internal forces using an inverse dynamics process based on differences between joint angles of tracked body parts of the plurality of body parts tracked from a previous frame and a set of desired joint angles for the tracked body parts for the current frame as determined from motion capture data, the velocities of each of the tracked body parts and the masses of each of the tracked body parts, wherein the positions calculated are constrained by at least one joint strength constraint or joint velocity constraint;
- and
- generating the current frame using the new set of positions obtained after the application of the forces to the plurality of body parts.