CompuServe Messages

Bill, Here are a few answers…. >>1) What about Friction, Spin, etc. ? There is no friction in the initial release. DMM uses a point to polygon detection scheme that will need to be changed to a surface to surface scheme before friction is enabled. Rotational values can be input in degrees per second. >>2) How are dynamic force vectors, etc. *defined* in 3DS/DMM ? Gravity and Wind are defined by entering a magnitude value (in meters per second), and a direction (input via X, Y, and Z values. >>3) What forces are available (gravity, turbulence, etc.) ? Gravity and wind as globals, velocity, acceleration, angular velocity as locals. >>4) Are all forces fixed or variable ? Forces are constant in the 1.0 version. We will have provisions for variable force in a subsequent release. >>5) How are objects to be used in CD identified & bound ? Objects may fall into one of four categories: A) Keyframed All keyframed motion is left intact. The only physical attribute that matters is the elasticity setting. B) Dynamic Object is affected by global factors of gravity and wind, and can have any combination of local variables. Mass, and elasticity, drag, along with motion settings of acceleration, velocity, and angular velocity can be adjusted. C) Key>Dyno Object is left keyframed until a collision is detected, at which time it becomes dynamic. This enables animations to be set up by keyframing paths so that objects will collide. D) Ignore Any object with the Ignore setting will not be calculated in the detection process, speeding up the generation time. >>6) Are there trade-offs available wrt CD precision vs calculation speed, etc. ? Not really. We are always in complex detection mode meaning that collisions may take place between objects of any shape and size. The polygon normals are examined for proper detection. There is a samples per frame setting that determines the resolution of the calculation. By default, DMM calculates collisions at 1/30th of a second. Objects travelling at a high rate of speed may penetrate, or pass through an other object between one frame and another. The resolution may be increased to nearly 1/500th of a second for such situations. The higher the resolution, the slower the calculation. For most animation needs, the default value of 1/30th of a second is sufficient. >>7) Does it only feature "rigid body" dynamics, or can colliding objects break apart, or deform each other due to the collision forces ? Rigid body. However, an object chopped into many smaller objects may break apart after a collision. >>8) How fast are the calculations ? (I'm aware this sort of thing is typically slow) It is entirely dependent on the number of faces and vertices. >>9) I assume that the routine can only operate on "normal" 3DS objects, rather than perhaps AXP-generated particles, etc. ? You are correct sir. There may be some developments in this area. Brent