Particle Size


#1

Hey

Is it possible to change the particle size in Krakatoa?

Thanks
M


#2

The simple answer is No, but reality is a bit more complex.

In Particle (Point) Rendering mode, each particle is assumed to be “point-sized”, and carries a few values including Density.
Then this point is drawn on screen and the resulting size depends in the filter mode. When set to Nearest, all of the particle will be drawn into a single pixel. When the filter mode is set to Bicubic, the particle will be drawn into a grid of 3x3 pixels. When set to Bilinear, it defaults to drawing into a grid of 2x2 pixels, unless you change the filter size.

The intensity (and Alpha, when rendering Volumetrically) of the particle, the amount of light it blocks etc. depend on the Density value. The Density expresses how much “matter” the point represents in a unit of space that the pixels represent. As result, if you have a row of particles whose Density changes from 1.0 to 0.0, visually it will appear that the particles are getting smaller. This is the same effect used for Anti-Aliasing in normal rendering - the fainter the pixel, the less coverage it implies, and your brain interprets it as “less matter behind that pixel”. This is quite obvious when rendering Hair with Krakatoa (mostly in the Max version as KC4D does not support Hair yet).
In the image below, you can see how in the first 3 examples the hair appears to be getting thinner as the Density falls off towards the tip, while the bottom right example has every hair strand with constant Density and thus constant thickness.

So you cannot get a particle much larger than a few pixels depending on the Filter settings, but you can make it appear smaller by reducing its Density.

The whole point of Krakatoa (pun intended!) is to draw so many particles that you see a continuous volume with the ability to represent very fine details and without being able to see the individual particles (unless you are trying to represent sand or silt).

The trouble with Point Rendering is that you cannot move through a dense cloud of particles without them dissipating into a “dust cloud” or “sand storm” look. That’s what the Voxel mode is for. There, we fill voxels with the particle data, and then shade the voxels instead. Thus, a “particle” cannot get any smaller than the voxel size, but fewer particles can create a continuous set of shaded voxels compared to Point rendering.