This operator selects particles that match one or all of the conditions that you have set on a per-channel basis. These conditions refer to the fluid properties of a selected FumeFX object at a given particle position. To use this: select the channels that you want to test; set the span of values that will be considered a match for that channel (or invert if you want to select values outside of that span); and, relax the test area with the Variation parameter. Then, choose whether you would like all or just a certain condition(s) to be met. As with many Particle Flow operators and tests, you can choose to interpret parameter keying in 3ds Max time, particle age, or event duration.
Pick / Remove - Use the Pick and Remove buttons to select a single FumeFX object.
Sync By: - Select which type of age to test against.
Absolute Age - This tests the current frame number in the animation.
Particle Age - This is the default test type. It tests the current age of each particle in frames.
Event Age - This tests the duration of the current event in frames.
The Test True If: option is helpful if you want to test the properties of more than one channel. With this, you can choose whether you want all channel conditions to be met or if just one condition will suffice.
Each of the following channels can be tested: Smoke, Temperature, Fuel, Fire, Color, Vorticity, Velocity and Flags, and they all share a number of common parameters for all of them.
First, selecting the checkbox next each channel name turns the test of that particular channel on or off.
Minimum and Maximum - For all channels except Flags, you can set limits to the span of values that will be considered valid.
Variation - Using this parameter, you can relax the boundaries of the test result area. It is defined as a percent of the selected Min and Max values.
Invert - You can also Invert this test so that the values outside of the Min/Max limits will be considered valid.
The Velocity group has an additional option that lets you select which particular component of velocity will be tested. Select from the dropdown list. Planes and axes are local to the FumeFX object. Units are defined as world units per frame. Also, you cannot differentiate the positive or negative direction.
If you select Velocity X, Y or Z, the test will only check the velocity component that is situated across the selected axis.
If you select Velocity XY, YZ or XZ, the test will apply to the velocity component across the selected plane.
If you select Velocity Magnitude, the overall velocity will be tested.
Vorticity is a virtual channel, dependent on the Velocity channel ??? similar to the way in which Fire is stored in the Fuel channel. Vorticity is calculated from the velocities of nearby voxels. Accordingly, this test will have no effect if the FumeFX output doesn't contain the Velocity channel. Vorticity refers to the small vortices, or curls in the fluid. So, with PF, you can test for particles in areas where smoke is curled. The amounts for the Vorticity channel depend on the velocities in the grid and the type of scene units; so the Min. and Max. values that you choose are highly dependent on the specifics of your scene/simulation. Experiment to find appropriate values.
The Flags channel is used to mark the presence of objects or sources in the fluid. This is not a test of all current scene objects and FumeFX Sources; rather, it only tests for objects that were used during FumeFX simulation. Even if these objects and sources have been deleted or moved or removed, their information remains stored in the Flags channel. You can use this channel to test for the following:
Source - This tests whether a FumeFX Source occupies a certain voxel.
Object - This tests whether an object occupies a certain voxel.
Next to Object - This tests whether an object occupies a neighboring voxel.