In the first subsidiary rollout, Shapes [Figure 12], you can set the basic geometric shape (sphere, cube, cylinder, torus, or variable hemisphere), maximum dimensions and rotation of the individual ‘puffs?making up your PC effect.

Selecting different shapes for the ‘puffs? can have a drastic effect on the result, and affords a great deal of flexibility when you are designing an effect. The dimensions and rotation of the ‘puffs?may be set for static scenes as well for animations, in which case the option to vary scale by velocity becomes active. Additionally, you can assign Auto-Rotation to an animated effect, or, by setting Use Object TM, incorporate rotational information implicit in trueSpace objects or in third-party particle systems in your scene.

The Shapes rollout also contains one of PC’s most useful tools for analyzing and tweaking your effects, the shapes Preview. When you activate this toggle, the selected effect’s ‘puffs?are rendered in your viewport in a wire screen mode based on their assigned shape and the volume that they fill in the scene. For the sake of clarity and efficiency, the maximum number of particles visible in the preview may be adjusted. Modifications made to such variables as shape, scale, rotation, and particle age and distance effects that affect the volume’s scale, are all dynamically translated to the wireframe preview in the viewport. Alterations to the character of a particle system are viewable too, but must be refreshed by toggling Preview on and off and on again before the changes are visible.

However, as can be readily seen in Figure 13, the wireframe preview shows the effect’s volume without taking into account the characteristics of the effect governing such factors as density and transparency.

In this simple instance, the volume of the effect is delineated by the preview, but the effect, because of characteristics defined in its parameters, appears somewhat less dense and more feathered at its upper extremities when rendered than the preview might lead you to believe. Nonetheless, this Preview mode can be invaluable in working with complex scenes for analyzing and adjusting where an effect’s volume might intersect with the scene’s mesh or with other PC effects. Such a use of the wireframe preview is shown in the following two shots of a PC effect in a scene from two different points of view, as well as a rendering of the scene. [Figures 14, 14a, 14b & 14c].