Previous Topic (Transparent Matte Objects And Multiple Layers Saving) Up (Tutorials) Next Topic (Using Krakatoa Geometry Test Operator)

Partitioning Using High-Frequency Noise in Krakatoa v1.1.2


Introduction

  • In general, Partitioning in Krakatoa is performed by saving the same dynamic particle system - Particle Flow, Thinking Particles or 3ds Max Legacy Particles - with varying Random Seed values to randomize parameters such as Position, Speed etc.
  • Unfortunately, this method cannot be used when the particles in question have been saved to file sequences, for example from RealFlow to a BIN file sequence, or from 3ds Max to a single PRT file sequence.
  • Furthermore, Geometry Vertices from a scene object have only positions but no velocities and cannot be directly randomized by Krakatoa when saving or when loading a PRT file saved from them.
  • To work around this limitation, the ability to change the Random Seed of Modifiers is available in Krakatoa v1.1.2 and higher.
  • Currently, the only modifier shipping with 3ds Max that exposes a Random Seed is the Noise Modifier, but the feature was written to support any modifier that exposes a "Seed" property.
  • Using specific settings to produce very high-frequency jittering, it can be used to produce slight variations of the original particle sequence or geometry vertices and result in a higher density particle cloud.

Partitioning Geometry Vertices

  • Create a Teapot with Radius 50.0 at the origin
  • Set the Segments to 24
  • Add a Noise Modifier to the Teapot
  • Set Scale to 0.1
  • Enable Fractal mode
  • Enter 4.0 for X, Y and Z Strength

The result is a high-frequency noise which jitters the vertices +/-4 units in object space.

  • Open Krakatoa GUI
  • Switch "Particle Render Mode" to "Save Particles To File Sequence"
  • Enable ">Geometry Vertices" in "Use Particles From"
  • Expand the "Save Particles" rollout and specify a file name
  • Expand the "Partitioning" rollout and enable ">Geometry Modifiers"
  • Press the "Generate All Partitions Locally" button. The default is 10 partitions. Since we are saving a single frame, you will be prompted to confirm you want that - two frames per partition will be actually saved.
  • While saving, watch the Command Panel - if the Noise modifier is visible there, you should see its Random Seed go up.

The result is 10 partitions with particles based on the teapot vertices, but randomly jittered in object space. Because the number of particles is 10 times higher, you would need to reduce the Volumetric Density by an order of magnitude to get the same result from the renderer. In other words, change the Exponent of the Density by -1.

  • Create a PRT Loader.
  • Add the first partitions and confirm the prompt about loading all partitions.
  • Switch "Particle Render Mode" to "Render Scene Particles".
  • Disable ">Geometry Vertices" in "Use Particles From", make sure "Particle Loaders" is enabled.
  • Render the PRT Loader

You should get 10 times more particles, diffused around the original particle locations thanks to the high-frequency noise.

The following image shows, from left to right:

  1. Original Teapot Geometry Vertices
  2. Same Teapot with Noise Modifier rendered as Geometry Vertices
  3. PRT Loader with all 10 Partitions, each original vertex represented by 10 jittered particles. 

 Note that all three objects on the above illustration were rendered at the same time. 
 To reduce the Density of the PRT Loader and produce the same apparent density in the final image 
 as the other two objects, the Visibility Track of the PRT Loader was set to 0.1, 
 thus scaling its Density locally to 10%.

Partitioning PRT Loaders

  • Krakatoa Particle Loaders support Deformation Modifiers like any other geometry object.
  • Thus, the workflow is identical to the method described above, except that
    • the Noise Modifier is applied to the PRT Loader instead of a geometry object,
    • the "Use Particles From" has to be set to ">Particle Loaders" when performing the Partitioning and
    • the ">PRT Loader Modifiers" option has to be checked in the "Partitioning" rollout.

All other steps are identical.

  • This approach can be applied to PRT, CSV and RealFlow BIN files to increase the density of the particle cloud by introducing more particles jittered around the original positions.
  • Since deformations are applied not only to the Positions of particles but also to their Velocity and Normal vectors, these channels (if available) will also be randomized by the Noise Modifier.