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Filtering ICE Particle Emissions

You can control from where particles are emitted by using a number of different Filter compounds, such as by weight maps, texture maps, within a volume, distance from a null or UV location on an object, or by object intersections.

With all Filter compounds, the particles are actually born first and then some are immediately deleted depending on the different criteria used for each compound.

Emitting Particles Based on a Weight Map

You can create a weight map on an emitter object and use it to define the particle emission using the Filter by Weight Map compound. This compound reduces the number of particles that are emitted based on the weight map values: particles are emitted only where the weight map has values over 0.

Using a weight map lets you emit particles from specific areas of the emitter object, especially when you want to emit particles using a gradient. Note that the resolution of the emitter’s geometry determines how detailed the weight map will be: the higher the resolution, the greater the potential detail.

Weight maps are discussed fully in Parameter Maps [ Scene Elements ].

To reduce the particle emission using a weight map

1. Select an object that will be the particle emitter and choose Get > Property > Weight Map from any toolbar. A weight map is applied and its property editor opens.

2. Press W to activate the Paint tool and paint on the weight map.

3. Create a particle emission—see Creating ICE Particle Emissions.

4. Open the ICE tree and click the Task > Particles tab in the preset manager on the left side.

5. Select the Filter by Weight Map compound from the Emission Control group, and drag it into the graph area.

6. Plug this compound’s Execute on Emit output into an Execute on Emit port of the Emit compound or a port on the ICETree node.

7. In the Filter by Weight Map compound’s property editor, use the Explorer button to select the weight map’s Weights attribute under the weight map you want to use. Weight maps are found under the object’s Clusters > WeightMapCls node.

Make sure that the string in the text box looks something like this (but using your “weight_map” name instead):

.cls.WeightMapCls.Weight_Map.Weights

You can also select the Invert option to use the inverse weight map values so that particles are emitted only where the weight map values are 0.

Emitting Particles Based on a Texture Map

You can create a texture map on an emitter object and use it to define the particle emission using the Filter by Texture Map compound. This compound reduces the number of particles that are emitted based on the texture map luminance (brightness) values (using an image or sequence): the darker the area of the texture map, the more particles are blocked from being emitted.

This lets you emit particles from specific areas of the emitter object, such as when you want to emit particles using a gradient or image pattern, especially an animated image sequence. And unlike with weight maps, the resolution of the geometry on which a texture map is applied is irrelevant. This means you can have more detailed particle emissions regardless of the resolution.

Texture maps consist of an image file or sequence and a set of UV coordinates. They are similar to ordinary textures, but are used to control parameters instead of surface colors. To create a texture map, you select a texture projection method and then link an image file to it, all in the texture map property.

To have particles take on the color of a texture map, see Using a Texture Map to Set the Particle Color.

To reduce the particle emission using a texture map

1. Select an object that will be the particle emitter and choose Get > Property > Texture Map from any toolbar. A texture map is applied and its property editor opens.

2. Select the texture projection method according to the emitter object’s geometry and then select an image or sequence to link to it. The texture projection maps the colors of the image to the geometry.

For more information on texture maps, see Texture Maps.

3. Create a particle emission—see Creating ICE Particle Emissions.

4. Open the ICE tree and click the Task > Particles tab in the preset manager on the left side.

5. Select the Filter by Texture Map compound from the Emission Control group, and drag it into the graph area.

6. Plug this compound’s Execute on Emit output into an Execute on Emit port of the Emit compound or a port on the ICETree node.

7. In the Filter by Texture Map compound’s property editor, use the Explorer button to select the texture map on the emitter that you want to use.

You can also select the Invert option to use the inverse texture map values so that particles are emitted only where the texture map values are 0.

Emitting Particles Based on Object Intersections

The Filter by Object Intersection compound reduces (filters out) the number of particles based on the emitter intersecting with another object. Particles are emitted only within that intersection area.

For best results, make sure that the intersecting objects are surface objects, such as polygon meshes or NURB surfaces.

To reduce the particle emission using object intersections

1. Create a particle emission—see Creating ICE Particle Emissions.

2. Click the Task > Particles tab in the preset manager on the left side of the ICE Tree.

3. Select the Filter by Object Intersection compound from the Emission Control group, and drag it into the graph area.

4. Plug this compound’s Execute on Emit output into an Execute on Emit port of the Emit compound or into a port on the ICETree node. If you do the latter, the emission is updated at each frame.

5. Select one or more objects and drag their names from an explorer into the ICE Tree graph to create a node for it. These are the objects that will intersect the emitter in order to emit particles.

6. Plug each object’s Value output into the Filter Geometry port on the Filter by Object Intersection compound.

7. In the Filter by Object Intersection compound’s property editor, you can set the Distance Threshold, which is the maximum distance (in Softimage units) around the object intersection area in which the particles are emitted.

You can also select the Invert option, which inverts the particle emission so that particles are emitted from the emitter except in the object intersection area.

Emitting Particles Based on a Volume

The Filter By Volume compound reduces (filters out) the number of particles based on whether or not they’re inside an object’s volume. The volume object must intersect with the emitter in order to emit particles.

To reduce the particle emission using the volume of an object

1. Create a particle emission—see Creating ICE Particle Emissions.

2. Click the Task > Particles tab in the preset manager on the left side of the ICE Tree.

3. Select the Filter by Volume compound from the Emission Control group, and drag it into the graph area.

4. Plug this compound’s Execute on Emit output into an Execute on Emit port of the Emit compound or a port on the ICETree node.

5. Select an object with volume (such as polygon mesh or NURBS surface) and drag its name from an explorer into the ICE Tree graph to create a node for it.

This object must intersect with the emitter at the point where you want to emit particles.

6. Plug the object’s Value output into the Volume port on the Filter by Volume compound.

7. In the Filter by Volume compound’s property editor, you can set the falloff profile curve and distance value to determine how the particle emission is filtered.

You can select the Invert option to invert the graph so that so that particles are emitted from the emitter except in the volume intersection area.

For more information on the parameters, click the ? icon in the property editor or see Filter by Volume.

Emitting Particles Based on a Null Shape

The Filter By Null compound reduces (filters out) the number of particles based on whether or not they’re inside a null’s icon shape. The null must intersect with the emitter in order to emit particles.

To reduce the particle emission using the shape of a null

1. Create a particle emission—see Creating ICE Particle Emissions.

2. Click the Task > Particles tab in the preset manager on the left side of the ICE Tree.

3. Select the Filter by Null compound from the Emission Control group, and drag it into the graph area.

4. Plug this compound’s Execute on Emit output into an Execute on Emit port of the Emit compound or a port on the ICETree node.

5. Create a null and open its property editor. Select an Icon shape that has volume, such as Box, Pyramid, Arrow Rings, etc.

The null must intersect with the emitter at the point where you want to emit particles.

6. Select the null and drag its name from an explorer into the ICE Tree graph to create a node for it.

7. Plug the null’s Out Name output into the Null Name port on the Filter by Null compound.

8. In the Filter by Null compound’s property editor, you can set the falloff profile curve to determine how the particle emission is filtered over distance.

You can select the Invert Filter option to invert the graph so that so that particles are emitted from the emitter except in the null intersection area.

Emitting Particles Based on Distance to a UV Location

The Filter By Distance to UV Location compound reduces (filters out) the number of particles based on the distance of a specific UV location on a NURBS surface or curve object to the emitter. Particles are emitted only when this location on the object is within a certain distance of the particle emitter object.

To reduce the particle emission using distance to a UV location

1. Create a particle emission—see Creating ICE Particle Emissions.

2. Click the Task > Particles tab in the preset manager on the left side of the ICE Tree.

3. Select the Filter by Distance to UV Location compound from the Emission Control group, and drag it into the graph area.

4. Plug this compound’s Execute on Emit output into an Execute on Emit port of the Emit compound or a port on the ICETree node.

5. Select a NURBS surface or curves object and drag its name from an explorer into the ICE Tree graph to create a node for it.

6. Plug the NURBS surface or curve’s Value output into the Geometry port on the Filter by Distance to UV Location compound.

7. In the Filter by Distance to UV Location compound’s property editor, select the UV location on the object to use and set the Distance Threshold, which is the maximum distance (in Softimage units) from this NURBS curve or surface to the particle emitter at which the particles will be emitted.

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