ICE: Scaling Particles From Bottom

A user on XsiBase was asking how to scale box particles from the base of the particle rather than from the center.

The easiest solution, if all particles are oriented upward, would be to add 1/2 of the yScale to the y position of the particles.  The problem arises when the particles are oriented out to the side.  Rather than just moving the particles upward, we need to move them along the direction they are pointing in.  This is easily accomplished by multiplying 1/2 of the yScale's 3d-vector (0,yScale/2, 0) by the rotational 3x3 matrix of the particle, and adding that to the particle's position.

Asteroid Test

Softimage ICE Asteroid test.  I encountered a problem when I tried to rotate the center null, but I thought it looked kinda cool so I did a quick render.  I think the way to fix this is to create null and disc at world origin, and then multiply the particle's 4x4 matrix by the null's 4x4 matrix to allow you to reposition and rotate the asteroid field.

https://vimeo.com/47069125