RenderMan DSO

Operation

There are two forms of the XGen RenderMan procedural: patch and face. The rib generator is responsible for putting the patch level procedural calls into the rib. XGen expands those into face procedurals when, and if, the patch procedural is cracked open. It is only when the face procedural is cracked that primitives are generated and therefore any real rendering begins. It is the patch procedural that takes all of the flags given below. A bounding box must be given for the patch procedural. It must bind all of the faces and all of the primitives that are to be rendered. If it is too small, clipping occurs. If it is too large, the procedural cracks open too soon and memory is wasted. The bounding box should bind all motion samples for that patch.

When a patch procedural is cracked, it parses the parameters. If it determines that this is the first time that the given palette has been hit, it loads in the palette file, reads the appropriate geometry for the motion samples, and caches it. It then emits face procedurals for all of the faces on the named patch. If the palette has already been cached, then the file is not read, but instead the process skips ahead and begins emitting the face procedurals for the named patch.

The palettes are cached based on their name, which includes the name of the nameSpace. This allows the same .xgen file to be used multiple times in order to populate a forest or a crowd. However, you must give each instance a unique name so that they do not end up sharing geometry inadvertently. For example, you have two trees that share the same .xgen file and share the same .caf animation file, but are offset by 50 frames in the animation cycle. You must give one tree a nameSpace of tree1 and the other a nameSpace of tree2. If you do not, then the first tree would come in and get cached. The second would come along and simply find the first cache and use it. The geometry for the second would never get loaded and the trees would be identical.

The geometry files are cached separately from the palette files, allowing for greater sharing. For example, the same geometry is often used multiple times, even within the same palette. You may have a forest of trees where a few are the same. Memory can be saved by allowing sharing. The XGen palettes would not be shared, but the underlying geometry would.

Arguments

The procedural takes a number of arguments as flags. Each is listed below with a brief description and an indication as to whether or not it is optional.

RenderMan Settings

A collection of settings are required within the rib file. These are settings that are not suited for the xgen file, as it would make the file specific to a frame, camera, or render phase (color versus shadow). It is often useful to bake out a rib that contains elements such as wind cycles, and then instance that rib throughout a scene. These RenderMan settings allow this to be done while each element still renders as if it were rendered in that position (that is, face camera, culling, level of detail all still work).

# directory for writing temp files
Option "user" "string irCacheDir" ["/disk1/tmp/renderPipeTemp12766"]

# the current render phase
Option "user" "uniform string phase" ["Shadow"]
Option "user" "uniform string generator" ["key_dir"]

# the 'current camera/generator' (once in rib)
Attribute "user" "string irCurrentCam" ["true, -0.633307, -0.591462, -0.499094"]
Attribute "user" "string irCurrentCamFOV" ["90, 90"]
Attribute "user" "string irCurrentCamXform" ["0.773158, 0.0338928, 0.633307, 0, -0.511791, 0.623091, 0.591462, 0, -0.374562, -0.781414, 0.499094, 0, 0, 0, 0, 1"]
Attribute "user" "string irCurrentCamRatio" ["1"]

# tell xgen the 'render camera' (once in rib)
Attribute "user" "string irRenderCam" ["false, 5.33365, 7.04902, 14.19"]
Attribute "user" "string irRenderCamFOV" ["54.4321, 54.4321"]
Attribute "user" "string irRenderCamXform" ["0.93606, -0.148352, 0.319037, 0, 0, 0.906762, 0.421643, 0, -0.351842, -0.394683, 0.848783, 0, 0, 0, -16.718, 1"]
Attribute "user" "string irRenderCamRatio" ["1.94445"]

The irCacheDir is used for writing out dra files when using the DRA render method. There is an assumption that when rendering the shadow passes, the directory is one level deeper than when rendering the color passes. The phase indicates the type of render: Color or Shadow. The assumption is that all shadow renders occur before the color render. If the phase is Shadow, then the name of the shadow generator is given with the generator option.

The next two sets of values represent the cameras being used. The first is the irCurrentCam, and represents the current camera or shadow generator. The example shown is a shadow render, and so the current camera is a shadow generator (that is, a light). The first value is a bool indicating if the camera is orthographic, and the next three values are the position (if the camera is perspective); or, the direction (if orthographic). The irCurrenCamFOV is the field of view for the camera (values for orthographic are 90,90; as shown). irCurrentCamXform is the inverse camera transform. Finally, irCurrentCamRatio is the ratio for the camera at 2k and is used for stochastic level of detail. This final attribute is computed as 2.0*focalLength/25.4044/horizontalFilmAperture.

The next set of values is irRenderCam, and they represent the camera for the color pass. If possible, both sets of values should be provided for all renders. If you are unable to produce both sets, and can only provide the values for the current camera, then pass those values into both sets of attributes.

Config Variables

There are a few config variables available for controlling the renderer as well. Some of these are specific to the DSO, and some are general, but since they all affect the process, they are included here as reference. When these variables are set, they override any flag value given above.