You can assign color and color variance to emitted particle types. For convenience’s sake, color information appears on the Color page in the Particle Type property editor so that you don’t have to open a shader when setting up the display color of the particles.
Anything you set here is used by the shaders, but you can also override the color with the Particle Color or Particle Gradient shaders. If you want to define the color as a ramp (for doing color shifts), use the Particle Gradient shader. This shader works according to a particle’s Age % by default.
For information on these shaders, see Rendering the Particle Color.
Setting the Particle Type’s Color
To set color properties for particles
1. Open the particles’ Particle Type property editor.
2. On the Color page, specify the color information of each particle type by using these controls:
You can animate the RGB and Alpha channels like other particle type parameters using the Birth, Age, Absolute, and Age % controls. For more information on this, see Animating Particle Type Parameters.
The Color - Variance parameters allow you to add variance to the H (hue), L (luminance), S (saturation), and Alpha parameters’ values. The values for parameters define the range in which the random numbers are generated.
The distribution method of the variance can be Uniform or Gaussian:
• With Uniform, random numbers are distributed uniformly around the parameter’s value using the Variance value. The parameter will always be in the range [ Value - Variance; Value + Variance ], never outside of it.
• With Gaussian, random numbers are distributed as a bell curve around the parameter's value using the Variance value. Most numbers will be in the range [ Value - Variance; Value + Variance ], but they may be outside of that range with [Value - Variance], and they will be outside of that range with [Value + Variance]. Values using Gaussian distribution will have greater variations than the ones using a Uniform distribution.
If you have the same value for both the parameter itself and the Variance parameter, different numbers result depending on the type of distribution you select. Numbers using Gaussian distribution will have greater variations than the ones using a Uniform distribution.
The seed parameter (the text box with no label to the right of the Uniform/Gaussian parameter) allows you to change the effect on the variance without changing either the parameter's value or its Var value. The seed defines which numbers will be generated in the range that the Var parameter specifies. It allows you to have very fine control over the parameters, changing them slightly without having to change the parameter’s value or its Var value.
The Seed parameter works only if you have a value other than zero for the Variance parameter to which it is associated.
Setting the Initial Color of the Emitted Particles
The Map Color option on the Emission property page lets you use the color values from a texture or vertex color map (using an image or sequence) that is connected to this option. When you select Map Color and connect a map, the colors on the map are used to set the initial color of each emitted particle. In this case, the particle color set on the particle type’s Color page is not used.
However, you can use the Jitter parameters (H, L, S and Alpha) on that page to modify the mapped particle colors.
Example: Mapping Colors to Particles
This is a simple example of how to change the emitted particle colors using the colors from a cloud image and a texture map. For more information on other parameters that can be mapped, see Parameter Maps.
1. Create a grid and make it larger than the default.
2. Choose Create > Particles > From Selection and accept the defaults.
3. Select the grid (particle-emitting object) and choose Get > Property > Texture Map > XZ to create the XZ projection and a texture map for this projection.
4. In the explorer, click the Texture Map icon under the grid’s node.
5. In the Texture Map property editor that opens, click the New button and choose New from File.
6. In the browser that appears, navigate to the <Softimage installation>\Data\XSI_SAMPLES\Pictures folder and select the cloud02.pic image to use as the map. Close the property editor.
7. In the Emission property editor, activate the Map Color option.
8. Click its connect icon and choose Connect. In the pop-up explorer, select the texture map you just created.
9. Still in the Emission editor, increase the Rate of particles to a larger amount such as 1000.
10. On the Particle Type > General page, set the Max Life to 10 or more, or select Live Forever so that there is enough time to see the effect of the texture map emerging.
11. In the Top view, select the Shaded or Textured display mode and play the particle simulation to see the colors of the cloud emerging in the particle formation.
Autodesk Softimage v.7.5