### Hiders

Pixie can generate images using raytracing or scan line rendering. As it is often the case, scan line rendering is much faster than raytracing. However, such methods may not support accurate reflections/shadows. Since Pixie supports both types of algorithms, you can combine the best of the two worlds: speed of scan-line rendering and the accuracy of raytracing. A hider is the section of the renderer that is responsible for creating the final image. Essentially, every hider implements a different rendering algorithm. You can switch between defined hiders using Hider command. Pixie defines the following hiders:

raytrace

As the name implies, this hider creates the final image using raytracing. This involves shooting bunch of rays for every pixel (defined by PixelSamples) and then filtering and summing the color of every ray (defined by PixelFilter). This hider also supports adaptive supersampling which means the renderer will only shoot rays when something interesting is going on (i.e. there is high frequency detail). The maximum allowable contrast can be specified using PixelVariance command.

stochastic/hidden
(Default)

This hider creates the final image using scan-line techniques very similar to Pixar's Reyes architecture. Every specified primitive is split into smaller primitives and deferred until needed. If the projected size of a subdivided primitive is small enough, a regular grid is sampled on the patch and the polygons in this grid are rendered using scan-line methods. Notice that a raytracer may need to keep the entire scene geometry in the memory in case a future ray can intersect them. On the other hand, the deferred and render-and-forget feature of this rendering algorithm allows it to keep a very small memory footprint

zbuffer | This hider is a stripped down version of Stochastic. It does not support motion blur, depth of field or transparency. If your scene does not involve these effects, this hider can generate an equal quality output with the Stochastic.
opengl | This is exactly the same with Zbuffer. However, the final stage of the rendering is implemented with OpenGl. The potential hardware acceleration makes this hider much faster than any other hider. If your computer does not have a hardware implemented opengl driver, Zbuffer is faster. OpenGL hider is only available on Windows systems for the time being.
photon | This hider is used to compute photonmaps in a preprocessing step. This hider does not create an image. The renderer simply goes through the light sources defined in a scene and shoots photons.

If you notice, OpenGL hider is implemented as a module. That means if you want to use it, opengl.dll/so must be in your procedural path (check "searchpath" "procedural" option).

The following table summarizes the capabilities of each renderer:

| TSM | J | T | OC | AOS | SS | ASS | MB | DOF
stochastic | X | X | X | X | X | X | X | X | X
raytrace |  | X | X |  | X | X | X | X | X
zbuffer |  |  |  | X |  | X |  |  |
opengl |  |  |  |  |  | X |  |  |
photon |  |  |  |  |  |  |  |  |

Where:

TSM | Transparency Shadow Map
J | Jittering
T | Transparency
OC | Occlusion Culling
AOS | Arbitrary Output Samples
SS | SuperSampling
ASS | Adaptive SuperSampling (no laughing)
MB | Motion Blur
DOF | Depth of Field

The RenderMan (R) Interface Procedures and RIB Protocol are: Copyright 1988, 1989, Pixar.