Creating a Particle Simulation
To create a particle simulation, you start out by creating a particle cloud that is associated with the object you have selected to be the particle emitter. This can be either a default emitter shape or any object in your scene.
A particle cloud is a container object for all the information about the particle system. The cloud is a “cloud of points” that results from the particles operator (simulator), but it has no inherent topology of its own (that is, its points are not connected together to form a surface). A cloud also has no properties of its own, which matters if you want to use scripting with particles.
When you create a particle cloud, you define the global characteristics of the particle simulation, which are generated by the particles operator. It generates and updates the particles for the cloud, considering the emitting object and its properties, natural forces, and obstacles.
Multiple Particle Clouds and Emitters
You can have any number of particle clouds in a scene. Each particle cloud has its own volume shader with its own personal space, but you can overlap them in position.
To keep your scene simpler, however, you can attach multiple emitters to a single particle cloud (see Adding Multiple Particle Emitters to the Same Cloud). You can then define a different particle type for each of the emitters (one particle type per emitter) to create totally different particle streams from one cloud.
To create a particle cloud
1. Do one of the following:
- From the Simulate toolbar, choose Create > Particles > From Primitive > From Cube, Disc, Sphere, or Grid to create a polygon mesh primitive object from which particles are emitted.
You can transform and deform this object as you would any other polygon mesh object in Softimage.
or
- Select an object that will be the particle emitter and choose Create > Particles > From Selection. You can use any type of object to be an emitter except a cluster.
If you want to change the emitter object later, see Setting Up the Particle Emission.
A particle cloud appears in the viewports, close to the global origin.
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• You can move the emitter object away from the particle cloud, but it is not recommended to move the particle cloud away from the global origin. • You can display or hide just the cloud icon in a viewport by toggling the Control Objects option in the visibility menu (click the eye icon). The particles themselves are still visible even if their cloud icon isn’t. |
2. In the ParticlesOp property editor that is displayed, set up the following options to define the particle simulation.
To open only the ParticlesOp property editor later on, select the particle cloud and choose Modify > Particles > Edit Simulation.
3. Set the particle emitter’s properties on the Particle Emitter pages, as described in Setting Up the Particle Emission. You can also do this later.
4. Set up each particle type to be associated to the particle cloud and emitter on the Particle Type pages, as described in Creating Particle Types. You can do this later as well.
Choosing the Way Particle Simulations Are Played Back
The way the particle simulation is updated depends on what you have chosen as the execution state when you create a particle cloud. You can play back the particle simulation and have all changes you make to the particles updated continuously (Live), you can calculate the changes only when you want (Standard No Caching), or you can cache the PTP files to play back as you like (Standard Caching).
For information on playing a simulation and caching PTP files, see Playing Particle-based Simulations.
Selecting a Playback Mode
You can set these Execution State > Mode options on the Simulation page in the ParticlesOp property editor:
• Standard No Caching (default) calculates the particle animation only when you click the Simulate button or go to a different frame, either by clicking the Play button below the timeline or moving the playback cursor.
This is useful for setting keys for the animatable particle properties or obstacle animations because you can move forward on the timeline without having to wait for the particle simulation to update. This mode doesn’t cache any PTP files, so you can’t play the simulation backwards.
• Standard Caching writes (caches) one PTP files for each frame in the simulation sequence, according to the Output Sequence name you have specified on the Output page in the ParticlesOp property editor (for information on PTP files, see Caching the Simulation in PTP Files).
When you first play the simulation, the PTP files are written so it takes a bit of time. However, once the PTP files are written, playback is faster than when no files are cached. As well, caching PTP files allows you to scrub the simulation and get the correct state, play the simulation forward or backwards, and play PTP files in the particle player for previewing (see Playing PTP Files in the Particle Player).
• Live mode allows you to play a simulation continuously for quick editing and tweaking. You can then view the effect of any modifications in real time.
Live mode is best when you play the simulation with looping on—this way you can tune parameters and immediately see what happens. Any change you make to a particle’s properties affects the particles from that point on: the simulation is not recalculated from the start. As soon as you skip forward, the simulation is computed from the current frame for all of the intermediate frames. The simulation is calculated using all the particles born at the current frame: all the particles are regenerated only when the simulation is started again from the first frame.
When you drag the playback cursor forward in the timeline, the particle cloud is frozen and won’t update until you click the Play button in the playback controls, which restarts the simulation from the first frame.
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Live mode is only used to view the changes you do on particles in real time when playing back, including viewing in the render region. However, when doing a final render or see the effects of motion blur on the particles, you need to use either the Standard No Caching or Standard Caching mode. |
To mute the simulation
• Select the Mute Cloud option on the Simulation page in the ParticlesOp property editor.
This option mutes the simulation and temporarily freezes the particle cloud in its current shape. It stops generating or reading through the PTP files, but since the last PTP file is still there, the particle cloud acts like a static object when you play back your scene. The particle simulator is fully disconnected so any changes you make to the particle’s parameters are ignored.
To recalculate the simulation from the current frame
• Click the Simulate button on the Simulation page in the ParticlesOp property editor.
This forces a re-evaluation of the simulation at the current frame, updating the particles to that point. The simulation is recalculated from the start frame to the current frame as soon as you modify a particle in a property editor or you move an obstacle or a force (if you’re not using Live mode).
Managing Time for a Particle Simulation
You can decide exactly when the particles are simulated using the parameters in the Time Management group in the ParticlesOp property editor. These parameters deal with creating a simulation source, which includes the simulator, the particle types, the emission properties, the events, and the obstacle properties.
• Set the Source Time to Local to determine the simulation’s time relative to the source. The animation for the emission properties, particle type, obstacle properties, and events are all taken starting at the scene’s time 1 and onward.
This means that you can create a simulation with animation on any of these properties that start at frame 1 and lasts n number of frames. Then you can offset the simulation in time and still keep the same result. This mode is useful for building simulation models and then retiming them as you like.
• Set the Source Time to Global (default) to determine the simulation’s time relative to the scene. The animation on any parameters is read from the scene’s start of the simulation up to the scene’s end.
This is useful when you know what the timing of the simulation is, such as if you need to add simulation effects between frames a and b in a scene by animating the source parameters between frames a and b (every element is properly placed in time).
To set the simulation’s length
• Set the number of frames for the Duration.
The Source > Start and End frames are calculated depending on what you set for the Duration. These frames are where the source animation is read from in the scene’s global time. These values are for display only and cannot be changed.
- When the Source Time is local, Start = 1 and End = 1 + Duration value.
- When the Source Time is global, Start = Global Result Start (which is the Offset value) and End = Start + Duration.
• Global Result > Start and End displays at which frames in the scene the simulation will be played. These values are for display only and cannot be changed.
To offset the simulation in time
• Enter a value for Offset. This is the number of frames by which you want to offset the start of the simulation.
With Local time, an Offset affects the place where the simulation is being played, but does not affect the source itself. This means that whatever the offset, the animation on the source is always read between frame 1 and 1+ Duration in the scene’s global time.
To match the scene’s and simulation’s frames
• Click Copy From Scene to copy the scene’s first and last frame defined for the timeline to the simulation. This changes the Offset and Duration so that the simulation is played throughout the scene’s timespan.
• Click Copy To Scene to copy the Global Result > Start and End frames to the scene’s timeline.
Deleting a Particle Simulation
Deleting a particle simulation removes the simulation and the particle cloud icon, but you must remove the particle emitter separately.
To delete a particle simulation
• Select the particle cloud icon and press Delete.
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