Particle Gradient Control

Particle Gradient Control | Render Tree Usage

Category: Particle

Shader Family: Texture

Output: Scalar

The Particle Gradient Control shader uses the input from other shaders from which it generates a gradient. The shader allows you to change ICE particle colors and/or density based on the particle's density, age percentage, or any particle attribute you define. For general information about ICE particle shaders, see ICE Particles.

The parameters in this shader control the position of a gradient (ramp) shader. They allow you to specify the criteria that is driving the gradient. The gradient's position is controlled by six attributes. The first two attributes (Density, Age %) are predefined while the other four attributes (Inputs 3 - 6) can be controlled by any input shader, such as an Attribute shader or a fractal texture shader.

You can set multiple options and have their results blended together, such as using both the particle's Density and Age % to determine the value set by the gradient.

Parameters

Per Cloud: Density

Uses the particle's density to drive the gradient. The density increases from the rim to the center of each particle. If there are multiple particles in the same space, their density is added together.

Gradient Starts At/Ends At

Uses the values on the gradient based on the particle density.

If the Gradient Start At value is set to 0 (particle rim), the value in the box at the left end of the gradient control is used.

If the Gradient Ends At value is set to 1 (particle center), the value in the box at the right end of the gradient control is used.

Intensity/Influence

Determines how the Density is weighted relative to the other attributes set on this tab.

For example, if the Density Influence is 0.6 and the Age % Influence is 0.3, then Density has twice as much influence on the final result.

Per Particle: Age %

Uses the particle's age percentage to drive the gradient. You must define the particle's age limit in the ICE tree so that the shader can use that value to set the values correctly — see ICE Particle Age for more information.

Gradient Starts At/Ends At

Uses the values on the gradient based on a percentage of the particle's age.

If the Gradient Start At is set to 0 (particle birth), the value in the box on the farthest left of the gradient control is used.

If the Gradient Ends At is set to 1 (particle death), the value in the box on the farthest right of the gradient control is used.

For example, if the Gradient Start At value is set to 0 the value at the left end of the gradient is used at the birth of the particle. But if the Gradient Ends At value is 0.5, only half of the particle's lifetime has been reached, so the values stop changing in the middle of the age of the particle.

Intensity/Influence

Determines how the Age % is weighted relative to the other attributes set on this tab.

For example, if the Age % is 0.6 and the Density Influence is 0.3, then Age % has twice as much influence on the final result.

Per Particle Input 3 - 6

These four inputs can use any shader to drive the gradient. They are controlled by shaders such as ICE Attribute shaders (see Bringing ICE Data into the Render Tree with Attribute Shaders for more information) or fractal texture shaders, such as the Fractal Scalar or Cell Scalar shader.

For example, using the Vector Attribute shader, you can use the particle's velocity to drive color gradient values so that the particles fade off or change color as they get faster. You can use any attribute that is defined for the particles in the ICE tree to drive the gradient.

Enable Input n	Toggles the activeness of this input.
Input	The value of the input shader.
Gradient Starts At/ Ends At	Sets the start and the end of the gradient based on the attribute value.
Intensity/Influence	Determines how this Particle Input is weighted relative to the other attributes set on this tab (Density, Age %, and other Particle Inputs).
Adjust Result (Otherwise Add to)	Adjusts the result of the input shader, if this option is selected. For example, say you have created a gradient that you like. Now you just want to add a little bit of variation to the gradient. With Adjust Result, you can use a new input shader, such as a fractal. The gradient on all the particles does not change much, just a bit of noise is added. If this option is unselected, you add the result of the shader, which has a more significant effect on the gradient.

Render Tree Usage

You can plug the Particle Gradient Control shader into any gradient port, such as the Per Cloud or Gradient Color and Density ports of the Particle Density shader or any gradient port on any of the particle shader compounds.

The Particle Gradient Control shader uses inputs from which it generates a gradient. There are two predefined inputs set up for you (Density and Age %), but you can also connect shaders to the shader's four Per Particle: Input (scalar) ports.

For example, you can use any of the Attribute shaders as inputs for this shader to drive the gradient based on almost any ICE attribute for the particles, such as their velocity, size, orientation, mass, point position, etc.