mental ray render node

Renders the scene using the mental ray renderer from mental images.

Overview

mental ray is a highly efficient fully featured ray tracing program written by mental images GmbH. It supports procedural shading, motion blur, global illumination, caustics, volumetric effects and many other features.

For more information see the mental images website.

Parameters

Render

Starts the render.

Render Control

Bring up the menu the rendering control options.

Valid Frame Range

Render Any Frame	Renders a single frame, based on the value in the playbar or the frame that is requested by a connected output render node.
Render Frame Range	Renders a sequence of frames. If an output render node is connected, this range is generally ignored in favor of frames requested by the output render node.
Render Frame Range (Strict)	Renders a sequence of frames. If an output render node is connected, this range restricts its requested frames to this frame range.

Start/End/Inc

Specifies the range of frames to render (start frame, end frame, and increment). All values may be floating point values. The range is inclusive.

These parameters determine the values of the local variables for the output driver.

$NRENDER	The number of frames to be rendered by the output driver.
$N	The current frame being rendered (starting at 1 and going to $NRENDER).

For example, if the parameters are set to:

Start	End	Inc
10.5	12	0.5

There will be 4 frames rendered (10.5, 11, 11.5, and 12), so $NRENDER will have a value of 4. $N will have the value:

Frame	10.5	11	11.5	12
$N	1	2	3	4

Render With Take

The output driver will switch to this take before rendering to restore the current take when rendering has been completed.

Main

The output driver is responsible for generating .mi files. These files describe the Houdini scene to mental ray. The Main tab determines how the .mi generation is processed.

Render Target	Choosing a target version of mental ray allows you to generate a .mi targeted to a specific build of mental ray.
Camera	The camera object which defines the scene.
Disk File	The location where the .mi file is saved to disk. You must turn on the Disk File checkbox to enable this parameter.
Command	The command where the .mi file is sent. This will be disabled if the .mi file is saved to disk.
Block Until Render Completes	When sending the output to a command, Houdini will normally return control after it is finished writing the .mi. This allows the render process to complete in the background. Turning on this parameter will force Houdini to block until mental ray finishes rendering the frame. When rendering a frame range, this option is automatically turned on. However, the option is not automatically turned on when rendering in an hscript or python loop construct. Therefore caution must be used or it is possible to end up starting multiple background renders. Note The rps and rkill hscript commands can be used to query or kill background renders. See the Troubleshooting section for more information.
Initiate Simulation OPs	If this option is turned on, POP and DOP simulations will be initialized before rendering.

Objects

The parameters on this tab determine which objects and lights are included in the .mi.

The order of processing these parameters is as follows:

Candidate objects/lights are selected.
Forced objects/lights are added.
Objects/Lights matching the exclusion parameter are removed.

Candidate Objects	The geometry objects in this parameter will be included in the .mi if their display flags are turned on and their display channel is enabled.
Force Objects	Objects in this parameter are added to the .mi regardless of the state of their display. Objects can only be added to the .mi once.
Exclude Objects	Objects in this parameter are excluded from the scene, regardless of whether they are selected in the Candidate Objects or Force Objects.
Solo Light	Only lights in this parameter will be included in the .mi. This includes shadow map generation and illumination. If this parameter is set, the candidate, forced, and exclusion parameters are ignored. Note Using this parameter in conjunction with the render_viewcamera property provides a quick way of generating shadow maps for selected lights.
Candidate Lights	Each light in this parameter is added to the .mi if the dimmer channel of the light is not 0. The standard light sets the dimmer channel to 0 when the light is not enabled.
Force Lights	The lights in this parameter are added to the .mi regardless of the value in their dimmer channels.
Exclude Lights	These lights will be excluded from the scene, even if they are selected in Candidate Lights or Force Lights__.
Visible Fog	The fog/atmosphere objects in this parameter are included in the .mi if their display flags are turned on and their display channel is enabled.

Properties

Camera

See the mental ray documentation for output statements.

Note

To view mental ray output in mplay when the File Type is Houdini mplay, you must use proto_install to install MiDisplay.

Open Houdini Command Line Tools.
Type proto_install.
Choose MiDisplay.

Sampling

Hover your mouse over the parameter names and use the reference in the tool tip to look up the corresponding information in the mental ray documentation for the Samples, Jitter, Contrast, and Time Contrast parameters.

Enable Motion Blur	mental ray will render the image using motion blur. The shutter parameter on the camera determines the duration of the shutter, specified as a fraction of the frame.
Xform Time Samples	The number of transformation blur motion samples. Each object (unless the parameter exists on the object) will have this many transforms output over the shutter duration. Increasing this number will result in smoother sub-frame motion, at a small memory and compute expense. Any number of segments may be specified.
Geo Time Samples	The number of deformation blur motion samples. Each object (unless the parameter exists on the object) will have this many copies of the geometry included in the .mi. When an object is deforming, increasing this parameter will result in smoother sub-frame motion blur. This option has no effect objects, which use velocity blur, since velocity blur is linear by nature. Note Any number of segments may be specified; however, duplicate geometry is sent down for each sample which may significantly impact the memory footprint of the output driver.
Geometry Velocity Blur	Blurs an image by using pixel velocity to produce a motion blur effect.
Motion Factor	This parameter automatically adjusts the shading quality for objects which are significantly blurred. When an object is blurred heavily, whether due to depth of field or motion blur, increasing the motion factor will automatically decrease the shading quality.

Hardware

Hover your mouse over the parameter names and use the reference in the tool tip to look up the corresponding information in the mental ray documentation.

Algorithms

Hover your mouse over the parameter names and use the reference in the tool tip to look up the corresponding information in the mental ray documentation.

Tesselate

Hover your mouse over the parameter names and use the reference in the tool tip to look up the corresponding information in the mental ray documentation.

Object

Hover your mouse over the parameter names and use the reference in the tool tip to look up the corresponding information in the mental ray documentation.

Scripts

Each script command refers to an hscript command which will be run, regardless of the expression language selected for the parameter. The resulting string will be run as an hscript command.

Note

It is possible to use the python, unix or source hscript commands to perform complex processing.

The commands are always run when rendering occurs. The command checks the parameters of the output driver when it is rendering a range or sending output to a command.

Before the render occurs, Houdini will automatically set the current hscript directory to point to the output driver.

Pre-Render Script	This command is run before any .mi files are generated. It is only run once per render.
Pre-Frame Script	This command is run before each .mi is generated.
Post-Frame Script	This command is run after each .mi is generated. Note Although the .mi may have been generated, this does not necessarily mean that mental ray has finished rendering the image when this command is run.
Post-Render Script	This command is run one time, after all .mi files have been generated. Note Although the .mi may have been generated, this does not necessarily mean that mental ray has finished rendering the image when this command is run.

Usages in other examples

Example name	Example for