Snow simulates falling snow or confetti. The snow system is similar to spray -- there are additional parameters to generate tumbling snowflakes, and different rendering options.
Kinds of Snow
The particle parameters for Snow appear in the Particles area of the Parameters rollout.
Viewport Count: Maximum number of particles displayed in viewports at any given frame.
Render Count: Maximum number of particles that can appear in a single frame when you render it. Works in combination with the particle system's timing parameters.
Flake Size: Size of a particle in the active units.
Speed: Initial velocity of each particle as it leaves the emitter. Particles travel at this speed unless they are affected by a particle system space warp.
Variation: Varies the initial speed and direction of particles. The greater the Variation, the broader the area of snowfall.
Tumble: Amount of random rotation for snowflake particles. This parameter can range from 0 to 1. At 0, flakes do not rotate; at 1, they rotate the most. The axis of rotation is generated randomly for each particle.
Tumble Rate: Speed at which snowflakes rotate. The greater the Tumble Rate, the faster the rotation.
Flakes, Dots, or Ticks: Select how particles are displayed in viewports. The display setting does not affect how particles are rendered. Flakes are star-shaped snowflakes, dots are points, ticks are small plus signs.
The rendering parameters for Snow appear in the Rendering area of the Parameters rollout.
Six Point: Each particle is rendered as a six-pointed star. Each side of the star is a face to which you can assign a material. This is the default setting for rendering.
Triangle: Each particle is rendered as a triangle. Only one side of the triangle is a face to which you can assign a material.
Facing: Particles are rendered as square faces whose width and height equals Size. Facing particles are provided especially for use with material maps
Note: Facing only works correctly in a perspective or camera view.
Timing parameters control the "birth and death" rates of emitted particles.
You set timing parameters in the Timing area of the particle system's Parameters rollout.
A particle system's Render Count is a creation parameter. It sets the maximum number of particles visible in the scene at any rendered frame. (Render Count is described in the topics that follow.)
At the bottom of the Timing area is a line that displays the maximum sustainable rate. This value is based on the Render Count and the lifetime of each particle. To be precise:
maximum sustainable rate=Render Count/Life
Because the number of particles in a frame never exceeds Render Count, if the Birth Rate exceeds the maximum rate, the system will run out of particles, pause until some die off, and then start again, generating bursts or spurts of particles.
Start: Number of the first frame where particles appear.
Life: The lifetime of a particle, in number of frames.
Birth Rate: The number of new particles born per frame. If this is less than or equal to the maximum sustainable rate, the particle system generates an even flow of particles. If it is greater than the maximum rate, the particle system generates particles in bursts. You can animate the Birth Rate parameter.
Constant: When checked, the Birth Rate parameter is disabled and the birth rate used equals the maximum sustainable rate. When Constant is unchecked, Birth Rate is enabled. Unchecking Constant does not mean that the birth rate varies automatically -- the birth rate remains constant at the Birth Rate setting unless you animate the Birth Rate parameter.
The emitter specifies the area where particles appear in the scene. It has a geometry you can display in viewports, but it isn't renderable.
The emitter is displayed as a rectangle with a vector pointing out of one side. The vector shows the direction in which the system emits particles.
You set emitter parameters in the Emitter area of the particle system's Parameters rollout.
Width and Length: You implicitly set the initial value of these parameters when you drag in a viewport to create the emitter. You can adjust the values in the rollout.
The height of the particle system is not specified by the emitter. It is implicitly specified by a combination of particle speed, set in the parameters specific to the kind of particle system, and particle lifetime, set in the timing parameters as described below.
Hide: Check to hide the emitter in viewports. When Hide is unchecked, the emitter is displayed in viewports. The emitter is never rendered.
The emitter's direction vector points in the negative Z direction of the active construction plane.