Exploring Shading

1 Exploring Shading

Rendering Vertices As Particles

The following is the beloved Teapot primitive rendered as a particle cloud (each vertex is taken as a particle, the maximum number of vertices of a teapot primitive with 64 segments is slightly more than 130K).

For the first example, let's use the default custom particle color (white) and a density of 0.05, which in the UI is expressed as two values; Density 5.0 and Density Exponent -2. This way, changing the Exponent (10^X) to -3 quickly gives you another zero after the decimal point. Going up with positive exponents can increase the density quickly by orders of magnitude like 10, 100, 1000 and so on.

This is the exactly same rendering, but using the wireframe color of the mesh:

The following example uses the self-illumination channel of a Standard 3ds Max material assigned to the teapot. It has a Cellular map to demonstrate that the channel is fully evaluated incl. any textures in it. Note that you have to either check the "Use Color" option in the Material for the Self.Illumination color to be used, or place the map in the Diffuse map slot and increase the numeric Self-Illum. Amount to 100.

Now let's switch to Volumetric Density mode - using the same setup and density values, but still no lighting. Thus, the teapot is self-illuminated:

Now let's add an Omni Light and turn Lighting on in the Krakatoa GUI. You can see the shadow casting, but also that light is passing through the particles (since only about 130K) and illuminating the backside (inside, bottom left) of the teapot:

Rendering Particle Flow Particles

Now it is time to use Particle Flow to emit particles from the surface of the Teapot while keeping all other settings identical. The Particle Flow is set to emit 1 million particles on frame 0 using a Position Operator with the Teapot as the surface to emit from. To avoid heavy self-shadowing of the particles when placed on the same surface, we can use an offset of 1 in the Position Operator to give the "particle teapot" a bit of thickness.

Note that we can control the density globally by changing the Exponent to -3 while keeping everything else identical (including the particle count of one million). Now we can see through the volumetric cloud:

The Volumetric Density mode only makes sense with lighting enabled. Here is what you would get from 1M particles with volumetric density but no lighting and no material:

Enabling the Lighting shades the particles as before. Let's use the default white particle color.

Animation Examples

Why would you want to render anything as a cloud of particles? Here is a possible situation illustrating what you could do with it...

This example contains 100 frames of 1 million particles. Rendering time on single CPU Athlon64 2.1 GHz with just 1GB of RAM was 22 seconds per frame incl. PFlow calculations, lighting and shading with 4 passes of motion blur. (each pass shaded in approx. 3 seconds, so 12 seconds was shading, the rest was calculating the flow and the lighting).