perform another simulation behavior when particles collide with things for example a target effect can cause the collided object to impinge a force on the collision object like wind striking a propeller another effect would be to have the particle bounce off of the object still another effect would be to have the object change the color of the location of the collision this would simulate the effect of spraying paint on the object the target effect could also record the collision with or without taking actions target effect modules can be complex for example the paint spraying function mentioned above requires a method for recording where particles have struck the object over the object 39 s lifetime this can be implemented as a texture map that is effectively a set of bitmaps that are positioned in 3d space relative to the surfaces of the 3d object the bitmaps are dynamically allocated for the object and modified during simulation a second bitmap is stored for rendering the object because rendering and simulation can occur at different rates the particle display module is executed by the rendering part of the simulation application and not during the simulation step the display module 39 s role is to use the drawing functions provided by the simulation application to render the particles in some way a particle array can be rendered as.