Aqsis Renderer Freedom to Dream

RI Standard Conformance

Required Features

Aqsis 1.2 and above implements all the required features of the RenderMan Interface Specification:

  • Hierarchical graphics state
  • Orthographic and perspective viewing transforms
  • Depth-based hidden surface elimination
  • Pixel filtering and antialiasing
  • Gamma correction and dithering before quantization
  • RGB, A and Z output, in any combination and any resolution
  • All the standard primitives and associated variables
  • Programmable shading using the RenderMan Shading Language (SL)
  • Texture maps, environment maps and shadow maps
  • All the standard shaders (implemented entirely in SL)

It is worth mentioning that Aqsis allows //all// shader types, including [[[doc:imagershaders|imager shaders]] to be written in SL, a feature that is still unsupported by most commercial renderers, including Pixar’s PRMan.

Optional Features

The set of required features in the specification is actually rather small, and Aqsis, like most other RenderMan-compliant renderers, also supports many additional features. The specification lists the following optional advanced capabilities. Some of them are implemented by Aqsis, and some are being considered.

  • Solid Modeling - supported
  • Level of Detail - supported
  • Motion Blur - supported
  • Depth of Field - supported
  • Special Camera Projections - not supported
  • Displacements - supported
  • Spectral Colors - not supported
  • Volume Shading - supported
  • Ray Tracing - not supported
  • Global Illumination - not supported
  • Area Light Sources - not supported

Interface Extensions

Aqsis supports a number of additional advanced features that are not mentioned in the RenderMan Interface specification. Most of these features are modeled after other renderers. This section provides overviews of the additional features in the style of the RISpec.

FIXME - write detailed specification (modelled on the RISpec) for each of the interface extensions.

  • ambient occlusion
  • Arbitrary output variables (AOV)
  • High dynamic range (HDRI) images
  • Dynamic shadeops (DSO)
  • Layered shaders

Ambient Occlusion

The ambient occlusion at a point on a surface is the amount of light which can reach that point directly from infinity. This provides a cheap kind of approximate global illumination - deep holes in a surface are dark and edges are highligthed when lit with an ambient occlusion light source.

The ambient occlusion may be computed by tracing rays in all directions from the point and finding which ones go to infinity, or by rendering depth maps from multiple points of view. Conceptually, the depth map approach is equivilant to having multiple ambient shadow lights lighting the scene from many directions, and is the method supported by Aqsis.

For a tutorial-style guide to using ambient occlusion, see [[guide:ao|Ambient occlusion]].

RtVoid RiMakeOcclusion ( RtInt npics, RtString picfiles[], RtString shadowfile, ...parameterlist... )

Create an ambient occlusion map from npics depth files stored in the array picfiles. The depth files should result from rendering the scene from multiple viewpoints. Depending on scene setup, such viewpoints are typically spaced evenly over a sphere or hemisphere centred on the object to be lit.


MakeOcclusion picfiles shadowfile ...parameterlist...

The number of input files is defined implicitly by the length of the picfiles array.


MakeOcclusion ["ao1.z" "ao2.z" "ao3.z" "ao4.z"] ""

Aqsis-specific geometry

The RenderMan interface defines a procedure RiGeometry for the purpose of implementation specific geometry types. Aqsis uses this interface to provide simple access to some of the more common geometry types familiar to the computer graphics community.

RtVoid Rieometry ( RtToken type, ...parameterlist... )

This procedure provides a way for implementations to provide custom geometry types. Aqsis provides the following additional types.

  • “teapot” - A bicubic patch mesh representing the classic Utah teapot.
  • “bunny” - A subdivision surface representing the Standford Bunny.


Geometry type ...parameterlist...


RiGeometry ( "teapot", RI_NULL );

RiGeometry ( "bunny", RI_NULL );

FIXME: document the following interface extensions -

Conditional RIB

RtVoid RiIfBegin ( RtString condition )

RtVoid RiElseIf ( RtString condition )

RtVoid RiElse()

RtVoid RiIfEnd()

Layered Shaders

RiShaderLayer ( RtToken type, RtToken name, RtToken layername, ...parameterlist... )

RiConnectShaderLayers ( RtToken type, RtToken layer1, RtToken variable1, RtToken layer2, RtToken variable2 )

Appendix: Additional filter functions