Introduction
This tutorial covers the basic issues of dealing with RenderMan's
Curves and issues relating to the specification of their normals. A rib file can
either specify the surface normals of a curve or it can let the renderer orientate the
curve so that is always faces the camera. Figure 1 shows four colored Curves rendered without
their normals being specified.
Figure 1
The rib file that rendered the curves is shown in listing 1.
Listing 1
ObjectBegin 1
Basis "b-spline" 1 "b-spline" 1
Curves "cubic" [8] "nonperiodic"
"P" [0.1 0 0 0.1 0 0 0.1 0 0
1 2 0 1.5 2 0 2 1 0
2 1 0 2 1 0 ]
"constantwidth" [0.125]
"Cs" [0.090 0.501 0.090 0.090 0.501 0.090
0.090 0.501 0.090 0.090 0.501 0.090
1 1 0 1 1 0]
ObjectEnd
Display "curve_normals" "it" "rgba"
Format 427 240 1
Projection "perspective" "fov" 40
ShadingRate 1
LightSource "distantlight" 1 "intensity" 2.5
"from" [0 0 0] "to" [0 0 1]
Translate 0 -0.8 4.7
Rotate -30 1 0 0
Rotate 40 0 1 0
Scale 1 1 -1
WorldBegin
ReadArchive "cutrAxes.rib"
AttributeBegin
Surface "plastic"
ObjectInstance 1
Rotate -90 0 1 0
ObjectInstance 1
Rotate -90 0 1 0
ObjectInstance 1
Rotate -90 0 1 0
ObjectInstance 1
AttributeEnd
WorldEnd
|
So that the b-spline curve starts and ends at it first and last control vertex
the the point data "P" duplicates the xyz's of the first
and last cv.
Figure 2
Figure 2 shows the same curves rendered with normals ("N") and the rib
file is shown in the next listing. It appears that with prman version 13 (and higher) the negative
z-axis scaling applied by the camera transformations requires the use of ReverseOriention
within the Attribute block. The scaling is applied so that the world coordinate system is
right-handed ie. it matches the handedness of Maya and Houdini. Refer to the tutorial
"Rib: Left-hand & Right-hand Coordinate Systems".
Listing 2
ObjectBegin 1
Curves "cubic" [8] "nonperiodic"
"P" [0.1 0 0 0.1 0 0 0.1 0 0
1 2 0 1.5 2 0 2 1 0
2 1 0 2 1 0 ]
"constantwidth" [0.125]
# arbitary normals!
"N" [0 1 0 0 1 0 0 1 0
0 1 0 0 1 0 0 1 0]
"Cs" [0.090 0.501 0.090 0.090 0.501 0.090
0.090 0.501 0.090 0.090 0.501 0.090
1 1 0 1 1 0]
ObjectEnd
Display "curve_normals" "it" "rgba"
Format 427 240 1
Projection "perspective" "fov" 40
ShadingRate 1
LightSource "distantlight" 1 "intensity" 2.5
"from" [0 0 0] "to" [0 0 1]
Translate 0 -0.8 4.7
Rotate -30 1 0 0
Rotate 40 0 1 0
Scale 1 1 -1
WorldBegin
ReadArchive "cutrAxes.rib"
AttributeBegin
ReverseOrientation #<<-- required
Surface "plastic"
ObjectInstance 1
Rotate -90 0 1 0
ObjectInstance 1
Rotate -90 0 1 0
ObjectInstance 1
Rotate -90 0 1 0
ObjectInstance 1
AttributeEnd
WorldEnd
|
The Basis statement in rib files generated by RenderMan for Maya Pro (RfM Pro) is shown below.
Basis [-0.166667 0.5 -0.5 0.166667
0.5 -1 0.5 0
-0.5 0 0.5 0
0.166667 0.666667 0.166667 0 ] 1
[-0.166667 0.5 -0.5 0.166667
0.5 -1 0.5 0
-0.5 0 0.5 0
0.166667 0.666667 0.166667 0 ] 1