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114 Chapter 17: Rendering
Use Fast R asterizer (R apid Motion B lur)—When
on, uses a fast rasterizer method to generate the
first generation of rays to trace. This can improve
rendering speed. D efault=off.
This option works well with object motion blur,
andalsowithscenesthathavenomotionblur.
The following settings are available for the fast
rasterizer:
•
Samples per Pi xel—Controls the number of
samples p er pixel used by the fast rasterizer
method. More samples result in greater
smoothness, at a cost of render time. Range=1
to 225. Default=16.
•
Sha des per P ixel—Controls the approximate
number of shading calls per pixel. Greater
values result in more accurate renderings, at a
cost of render time. Range=0.1 to 10000 (ten
thousand). Default=1.0.
•
Time Samples—When the scene uses motion
blur, controls the number of times the material
is shaded during each time inter val (set by
Camera Effects rollout (page 3–100) >Motion
Blur group > Shutter). Range=1 to 128.
Default=1.
By default, the material is shaded only once,
and then blurred. If the material changes
rapidly during the shutter interval, it might be
useful to increase this value, in order to obtain
more accurate motion blur. Rapid changes in
reflections or refract ions might require a higher
Time Samples value.
Ray Tracing group
Enable—When on, mental ray uses ray tracing
to render reflections, refractions, lens effects
(motion blur and depth of field), and indirect
lighting (caustics and global illumination). When
off, the renderer uses the scanline method only.
Ray tracing is slower but more accurate and more
realistic. Default=on.
You must turn on Ray Trace to render reflections,
refractions, depth of field, and indirect lighting
(caustics and global il lumination).
Use A ut ovol ume —When on, uses the mental ray
autovolume mode. When Autovolume is on,
you can render nested or overlapping volumes
such as the intersection of two spotlight beams.
Autovolume also enables a camera to move
through the nested or overlapping volumes.
Default=off.
To use Autovolume, Ray Trace must be turned on,
Scanline must be turned off, and the shadow mode
must be set to Seg ments. (You set the shadow
mode on the
Shadows And Displacement rollout
(page 3–111)
.) If these conditions aren’t met when
you click to turn on A utovol ume, an alert warns
you about this, and gives you the option of making
the appropriate setting changes.
Raytrace Acceleration Group
Method—The drop-dow n list sets which a lgorithm
to use for
rayt r ace acceleration (page 3–1094) .
The other controls in this group box change,
depending on which acceleration method you
choose. These are the alternatives:
•BSP(thedefault)
TheBSPmethodhasSizeandDepthcontrols.
See
Ray-Trace Acceleration: Parameters for the
BSP Methods (page 3–125)
.
This method is the fa stest on a single-processor
system. Use it for sma ll-to-medium size scenes
onasingleprocessor. BSPisalsothebest
method to use when ray t racing is turned off.
•Grid
TheGridmethodhasSize,Depth,and
Resolution controls. See
Ray-Trace
Acceleration: Parameters for the Grid Method
(page 3–125)
.
This method uses less memor y than BSP. It is
also faster than BSP on multiprocessor systems.