3Delight For Maya gives you the ability to execute MEL scripts at certain locations during the rendering. This opens up the possibility of doing whatever tweaks required before each rendering. Since 3delight comes with a set of MEL bindings for the RenderMan standard, it also becomes possible to insert RenderMan commands anywhere during rendering (see Chapter 6 [MEL Binding], page 130). This is the equivalent of “RIB Boxes” in other packages but with the added flexibility of a scripting language. In addition to the MEL scripts listed here, there are others available in geometry attribute nodes (see Section 3.5 [The Geometry Attribute Node], page 14) and in the light attribute nodes (see Section 3.8.8 [Light Attribute Node MEL Scripts], page 43).
The following variable is automatically defined in the context of these scripts execution:
‘string $render_pass’
This variable is assigned the current render pass node name.
Chapter 3: The User Interface 75
Figure 3.60: The MEL Scripts panel
‘Pre Render MEL’ ‘Post Render MEL’
Specify scripts to run before and after the rendering is finished, respectively. Those scripts are guaranteed to run first and last. They are also executed outside of any RiBegin/RiEnd block, so these scripts are not appropriate for invoking RenderMan commands.
‘Pre Frame MEL’ ‘Post Frame MEL’
Specify scripts to run before and after each frame, respectively. These two scripts are the very first and last things executed for each frame; they are called even before and after the RiBegin/RiEnd block, so these scripts are not appropriate for invoking RenderMan commands.
‘Post Option MEL’
Specifies a script to execute after all RenderMan options have been issued, but before the camera transforms. This can be used to override any option.
‘Pre World MEL’
Specifies a script to execute just before RiWorldBegin which is also right after where the camera transforms are issued.
‘Post World MEL’
Specifies a script to execute right after RiWorldEnd (but before RiFrameEnd).