Transformations applied before WorldBegin establish the spatial relationship of the world relative to the camera. Rib files produced by mtor make a call to a ConcatTransform statement. The statement specifies a transformation matrix of 16 values. The following example has been reformatted to more clearly show the 4 by 4 matrix of values.
ConcatTransform [ 0.707 -0.331 -0.625 0.0
0.0 0.884 -0.469 0.0
-0.707 -0.331 -0.625 0.0
0.0 0.0 44.822 1.0 ]
Although it is not obvious this matrix inverts the z-axis of the world
so that its coordinate system conforms to Maya's right hand coordinate system.
Fortunately, RenderMan provides more human-friendly statements for specifying
the same information.
The rib statements shown below in bold setup exactly the same world/camera
relationship as that specified by the (less readable) ConcatTransform.
The transformations
do not effect the current coordinate (camera) system but rather, as figures 2 to 6 will
show, they effect a copy of the current coordinate system.
It is often extremely helpful when debugging a scene or when developing a
shader to make use of a simple rib file rather than trying to deal with a
complex rib written by mtor. The following link compares
two rib files that
render exactly the same images.
1 2 3 4 5 6 7 8 9 10 11 12 |
Display "untitled" "framebuffer" "rgb"
Projection "perspective" "fov" 40
Format 427 240 1
Translate 0 0 5
Rotate -30 1 0 0
Rotate 45 0 1 0
Scale 1 1 -1
WorldBegin
ReverseOrientation
...
WorldEnd
|
Although the renderer "reads" the transformations in the order in
which they appear the effect they have may be considered to be the
result of the renderer applying the transformations in reverse sequence.
Figures 1 to 5 illustrate how the transformations are applied to
the coordinate system of the world.
figure 1 - active (left hand) coordinate system
before the transformations are applied
