ART Anim8or Ray Tracer
Introduction
With v0.97 Anim8or has an integrated Ray Tracer.  You can use it to render movies and still images just like to original scanline renderer and OpenGL shader renderer.  ALl you need to to is select it from he Renderer->Renderer command dialog.

Ray Tracing is a global rendering technique for making relatively realistic images from 3D models.  It traces the path that a light ray might take through the scene to discover what objects, lights, etc. affect the final color of a pixel.  It is called a global technique because any part of the scene may influence to final value of any pixel.  Ray tracing borrows from optics to model reflections, refractions and more.
Anim8or's ray tracer can render all of it's normal materials, of course.  But it also can show reflections off of shiny objects and defraction through transparent ones.  The next sections will explain how to add these effects to your images.

ART Materials
You enable the additional capabilities of ART materials by adding certain attributes to normal materials.  Attributes allow you to associate arbitrary values with a material.  The ART renderer check them when initializing a scene and chooses alternate rendering code when the right ones are present.  You add attributes to a material by clicking on the "Attributes" button in the basic Material Editor.  This section lists the main categories of ART materials.
The attribute class is the starting point for accessing ART materials.  class is a string attribute which defaults to normar Anim8or materials when not present.  Note that case is important in attribute names.  Class and CLASS are names for different attribuites and do not affect ART rendering.  In addition to the normal parameters of Anim8or materials, individual classes may use additional attributes for more flexibility.

The main classes are anim8or (the default), glossyreflector, transparent and dialectric.  Each is described in a following section.

Class anim8or
Class anim8or has additional attribute, specular.  It determines the look of the specular reflection.  There are 3 recognized values:
  • phong - the default value, phong is simple normal Anim8or phong shading for hilights.
  • reflection - a mirror like perfect reflection is added to a material.  Rays are reflected off of a surface to determine what is visible in that direction.  The result is multiplied by the materials specular weight, Ks, the material's normal color - including the original phong hilight - is weighted by (1 - Ks) and the tow values are added for the final color.  Thus a value of Ks = 1.0 would be a perfect mirror with no base material properties visible, and Ks = 0.1 would be a normal material look with a slight rfiection of the scene.
  • glossy - an imperfect reflection is added to the material.  This is like a blurred mirror or defocused camera image.  The further from a surface, the less distinct the reflection.  The overall amount of blurr is determined by the Phong Roughness.  THe default value of 32 is very rough.  Higher values like 1000 make a more perfect reflection while 100000 is almost the same as a perfect reflection.
    Glossy images need anti aliasing turned on or they will look very speckled.  Very glossy images will need more that the default AA samples per pixel value of 16.  The image below uses the default, 32, and the default samples per pisel of 16 and is rather grainy.
Below is an example of the three settings for the specular class.  From the left they are phong, reflection and glossy.  Ks is 0.5 and Roughness is the default of 32.

Here is the Anim8or project for the above image: class_anim8or.an8

Class glossyreflector
This glossyreflector class is a simpler class that is similar to the anim8or class with the specular attribute of glossy.  While the anim8or class is a little less accurate from a physical sense, glossyreflector attempts to follow the rules of physics a little more closely.

The glossy reflector class uses the Phong roughness value for the degree of glossiness.  glossyreflector has one attribute:
  • Kr - constant of reflection.  This is similar to the specular constant in normal Anim8or materials, Ks, but controls what percent of the light is reflected.  It is set to the value of Ks if there is no explicit Kr.
Below are three glossyreflector spheres with roughness of 200, 1000 and 100000.  You can still see quite a bit of graininess in the left sphere even though this image used 64 samples per pixel.  Glossy surfaces require many more samples for high quality images.  Also notice that there is no specular highlight from the infinite light source.  Infinite lights don't represent real, physical entities.  An area light would show a specular highlight however.

Here is the Anim8or project for the above image: class_glossyreflector.an8

Class transparent
The transparent class is a simple model for defraction of light through transparent materials.  There is also a slight reflection off the surface.  The amount of transparency is set with the normal transparency value for a material.  It has one additional attribute:
  • IOR - the index of refraction.  This represents how much light is bent as it enters or leaves a transparent material. Useful values include 1.0 (air - no difference than outside of a material), 1.33 (glass), 1.49 (Plexiglas) and 2.42 (diamond).
Rendering transparent materials can take a very long time.  Each primary ray (from the camera) can trigger tens or even hundreds of rays since each interaction generates up to two child rays, the reflected ray and the transparent ray.

The image below show 5 spheres with and IOR of 1.0, 1.1, 1.2, 1.3 and 1.5, and a transparency of 0.1:

Here is the Anim8or project for the above image: class_transparent.an8

Class dielectric
The dielectric class is a complex model that is closer to how light interacts with real transparent materials.  It uses Fresnel equations to determine reflections and transmission parameters at each ray-surface interaction.  As light travels through a dielectric material it is attenuated and gradually takes on the material's color.  Thin sections appear almost colorless but thick sections can be quite dark.  Glass is a dielectric which explains why a solid glass door looks clear from the front but looking into the edge can be dary green or gray.  The diaelectric class has two additional attributes:
  • IOR - the index of refrection.  As with the transparent class, this controls how much light is bent as in enters or leaves the material.
  • UnitDistance - the distance a ray must travel through the material to be filtered by the material's diffuse color.  The ray's color is multiplied by the diffuse color raised to the power of (the distance traveled/UnitDistance).  So if the diffuse color is (0.5, 0.5, 0.5) and UnitDistance is 10, then a ray that travels 20 units will be scaled by (0.5, 0,5, 0.5)^2 or (0.25, 0.25, 0.25).  The default value of UnitDistance is 10.0.
The image below shows several spheres and a rectangular prism that are dielectrics with an IOR of 1.3:

Here is the Anim8or project for the above image: class_transparent.an8

Light Attributes
You can modify the look of area lights by changing the way that they are sampled with the following attribute on the light in a scene:
  • sampler - is a string attribute with three recognized values: multijittered (the default), jittered, and regular.  The jittered modes produce a more random or  grainy effect when undersampled while the regular sampler looks more like multiple shadows.
The image below has two area lights, the blue one (the yellow shadow) uses a regular sampler while the white light (which makes a blue shadow) uses the default multijittered sampler.

This image was made with 16 samples per pixel.  Increasing the number of samples will make the images smoother.  Here is the project for this image: light_samplers.an8

Future Classes
More material classes are coming to Anim8or's ART ray tracer.  Stay tuned!

This page was last updated on March 19, 2008.
Copyright 2008 R. Steven Glanvlle