Tutorial 10: Effector and Falloffs


This tutorial should shed some light over three Effector's curves: Shape Falloff, Output Value and Radial Multiplier.


Please load Tut_10_start.ma scene in your Maya.


You will find a FumeFX grid and a box Effector. The FumeFX gird is contained within Effector so that the center of the Effector lies on the FumeFX's right boundary, and the left Effector boundary matches the left FumeFX's boundary.


Select fumeFXShape1 and open its relationship manager. Select ffxEffectorShape1 so that FumeFX will be able to use it. Scroll down to the Simulation - >Smoke rollout, click on the Master Effector button and under Channel Name type eff1. Now, the Effector is connected to the FumeFX Grid as the Smoke Master Effector. That means that it will directly affect the smoke channel in each voxel.



Select ffxEffectorShape1 and set Input Type to Constant, Output Operator to Replace and Scalar to 1. This will effectivly fill the FumeFX grid with low density smoke.


Effector like this will not be able to work in an emtpy grid, so open FumeFX UI and uncheck Adaptive checkbox and run the simulation.


After the simulation is done, open the FumeFX Preview Window. Scrub the time slider and notice how smoke fills the grid uniformly and nothing changes with time because effector replaces smoke values in every frame.



Let's say we want to add smoke to the grid in such way that it has more density near the center of the effector and less density near effector boundaries.


Select ffxEffectorShape1 and click on Use Radial Multiplier to activate it. Default curve looks as on the image below.




Run the simulation again.


As you can see, Radial multiplier curve has modified the output value based on the distance between the Effector's center and its boundary. As a result, the smallest smoke amount is applied to the voxels that are further away from the Effector's center.



Now uncheck the Use Radial Multiplier to disable it.


Under the Source rollout enable Use Shape Falloff to enable Shape Falloff curve.


Run the simulation.


Simulation looks the same (as with Radial Multiplier cyrve) in the first frame. But as the time progresses, smoke fills the grid until density is uniformly distributed.




Here is an explanation why those two methods become different as the simulation progresses.

Radial Multiplier curve is applied before the Effector operation (and after Output value curve) while Shape falloff curve is applied after. This means that the Radial Multiplier cuerve will set values based on the distance between effector center and effector boundaries, then these values will replace smoke densities of voxels in the grid.


On the other hand, in the last simulation Shape Falloff curve blended Effector value with values from the grid in a way that voxels closer to the Effector boundaries had the smallest influece from the Effector, while voxels closer to the center had maximum influence.


In each succeeding frame, the effector blended values from the grid (calculated in the previous frame) with calculated values based on the distance between the effector's center and effector's boundary, causing the grid to gradually fill with smoke.


Next, disable the Use Shape Falloff curve. Under the Input rollout change Input Type to Texmap Scalar. Click on the Map icon and from the 3D Textures list select Cloud.
For the cloud1 map set Contrast to 1.0, Amplitude to 0.6, Depth to 0 and 5.



Select the place3dTexture1 and set Scale to 30,30,30.


Select ffxEffectorShape1, activate the Output Value curve by enabling the Use Output Value Ramp, and set it to a linear curve.



Run the simulation.


You can see smoke has been created based on the map values.


Select FumeFX and from the FumeFX shelf, create new Effector.


Select ffxEffectorShape2 and set the Channel name to eff1; that's the same channel name as the first effector is operating on.


Set Output Operator to Replace, Scalar to 1.


Now open FumeFX Attribute Editor and open the FumeFX Compute Sequence Editor. Select the Effectors option to list Effectors. Make sure that our new Effector is appended at the end of the list.




Run the simulation.


The entire grid is filled with smoke.



You might wonder what happened to the first Effector; as both Effectors share the same area of influence. The order in which effectors are listed inside the the FumeFX Compute Sequence Editor list reflects the order in which they are applied. Since second effector uses a Replace operator (without Shape Falloff), it has written over and replaced values the first effector set.


Now reverse the order of the effectors; select first effector and click arrow to move it down.


Run the simulation.


Only effect of the FFX Effector01 is visible now.



In areas where the map is black, no smoke is created; in areas where the map is white, smoke density is set to Scalar value (in this case 1).