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or in the Modify panel at any time. The simpler systems, Spray and Snow, have a single Parameters rollout, but the advanced systems—Particle Flow Source, Super Spray, and Blizzard—include multiple Parameters rollouts. The PArray and PCloud systems have similar multiple rollouts, with a few subtle differences, and the Particle Flow system includes several rollouts, but most of the action is with the Particle Flow window. The following sections describe how to use these rollouts to set the parameters for the various particle systems.

Using the Spray and Snow Particle Systems

All I can say about the Spray and Snow particle systems is that when it rains, it pours. The Spray Parameters rollout includes values for the number of particles to be included in the system. These values can be different for the viewport and the renderer. By limiting the number of particles displayed in the viewport, you can make the viewport updates quicker. You also can specify the drop size, initial speed, and variation. The Variation value alters the spread of the particles' initial speed and direction. A Variation value of 0 makes the particles travel in a straight line away from the emitter.

Spray particles can be Drops, Dots, or Ticks, which affect how the particles look only in the viewport. Drops appear as streaks, Dots are simple points, and Ticks are small plus signs. You also can set how the particles are rendered—as Tetrahedron objects or as Facing objects (square faces that always face the viewer).

Note

The Facing option is visible only in the Perspective view but can be rendered using any viewport, including a camera viewport. •

The Timing values determine when the particles appear and how long the particles stay around. The Start Frame is the first frame where particles begin to appear, and the Life value determines the number of frames in which the particles are visible. When a particle's lifetime is up, it disappears. The Birth Rate value lets you set how many new particles appear in each frame; you can use this setting or select the Constant option. The Constant option determines the Birth Rate value by dividing the total number of particles by the number of frames.

The emitter dimensions specify the width and height of the emitter gizmo. You also can hide the emitter with the Hide option.

Note

The Hide option hides the emitter only in the viewports. Emitters are never rendered. •

The parameters for the Snow particle system are similar to the Spray particle system, except for a few unique settings. Snow can be set with a Tumble and Tumble Rate. The Tumble value can range from 0 to 1, with 1 causing a maximum amount of rotation. The Tumble Rate determines the speed of the rotation.

The Render options are also different for the Snow particle system. The three options are Six Point, Triangle, and Facing. The Six Point option renders the particle as a six-pointed star. Triangles and Facing objects are single faces.

Tutorial: Creating rain showers

One of the simplest uses for particle systems is to simulate rain or snow. In this tutorial, you use the Spray system to create rain and then learn how to use the Snow system to create snow.

To create a scene with rain using the Spray particle system, follow these steps:

1. Open the Simple rain.max file from the Chap 41 directory on the CD.

This file includes an umbrella model created by Zygote Media.

2. Select the Create⇒Particles⇒Spray menu command, and drag the icon in the Top viewport to cover the entire scene. Position the icon above the objects, and make sure that the vector is pointing down toward the scene objects.

3. Open the Modify panel, and in the Parameters rollout, set the Render Count to 1000 and the Drop Size to 2. Keep the default speed of 10, and select the Drops option; these settings make the particles appear as streaks. Select the Tetrahedron Render method, and set the Start and Life values to 0 and 100, respectively.

Note

To cover the entire scene with an average downpour, set the number of particles to 1000 for a 100-frame animation. •