Cometa

The Effects->Cometa command in the Motion module acts a simple particle system. You create an animated source polygon mesh and then specify the number of particles to assign to that polygon mesh. The result is a new polygon mesh object composed of particles that is animated according to the source polygon mesh animation. Each particle is a triangle.

There is a scene called Flow in the Rebels database that you can play with, but there is no tutorial for it.

Procedure

1. Create a source polygon mesh and animate it.
2. Choose the Effects->Cometa command. The Cometa dialogue box is displayed.
3. Set the parameters as desired and click Ok.
4. Pick the model.

The effect icon appears and a new model is created with the specified number of particle triangles.

Parameters

Particles

The number of particle triangles you want to create.

%

Specifies the percentage of the particle's visibility. For example, if you set a value of 0.5, only half of the particle is visible. You can animate this parameter to create particles that appear and disappear.

Seed

Determines how the random number generator is initialized. If you create two Cometa effects with the same seed, the simulations are always the same (that is, they use the same random numbers to calculate the effect). With different seeds, the random number changes, producing slightly different effects. You can use any number from 1 to 100 as a random seed.

Size

The size of each particle in SOFTIMAGE units.

Particle Positioning

Where to position the particles relative to the polygon mesh:

• Bounding Sphere: The particles are created within the bounding sphere of the selected model.
• Thickness: This number defines the thickness of the bounding sphere.
• Bounding Box: The particles are created within the bounding box of the selected model.
• Volume: The particles are contained within the volume of the selected model.
• Vertices: The particles are distributed on the vertices of the polygon mesh model, or on the control points of a patch or curve. If using a null object, then particles are distributed on the null itself.
• Edges: If the source model is a polygon mesh, the particles are distributed along its edges.
• Polygons: If the source model is a polygon mesh, the particles are distributed over its polygons. The polygons must be convex.
• Random: This option is available for the Vertices, Edges, and Polygons options. When you select it, particles are distributed randomly rather than in order of the vertices, edges, or polygons. This is useful if you are creating fewer particles than there are vertices, edges, or polygons.

Copy Model Rotations, Scaling, and Translations

The new polygon mesh inherits the selected transformation values from the source model.

Note:

You must select these options when using the Bounding Sphere and Bounding Box options.

Compute Normals

Select this option to compute the normal values on the resulting polygon mesh.

Refresh Seed

The seed value is changed at every frame.

Jitter

The particles are jittered randomly within a radius you set in the associated text box.

Wow

Makes the particles pulse in the jitter direction. The pulse is controlled by the sine function defined by setting frequency and phase values in the associated text boxes. Frequency is the number of frames to complete a cycle, and Phase is the shift in time for the sine wave.

Material

Copy from Model

If the Polygons option is selected, the particles inherit the colour of its host polygon. In other cases, the particles inherit the first material applied to the source model.

Random

The number of materials that you enter in the Materials text box are created and assigned randomly to particles.

Radial

The number of materials that you enter in the Materials text box are created and assigned randomly to particles according to the particle's distance from the centre of the bounding sphere of the output model.

Note:

All parameters set can be further edited or animated by selecting the icon and choosing Effects->Edit Parameters.

Next, Previous, Delete, Key, and Frame

To animate the effect, Next advances to the next keyframe, Previous goes back to the previous keyframe, Delete removes a keyframe, and Key sets a keyframe at the frame you specify in the Frame text box. These controls can only be accessed after you have set the initial parameters in the dialogue box and clicked Ok. To return to the dialogue box and edit keyframes for the effect, select the effect icon and choose the Effects->Edit Parameters command in the Motion module.

Last updated 02-apr-1998