Houdini plugin - Maxwell Render (ROP)

The Maxwell Render output operator is located in the TAB menu of the out network or can be added to the scene via the Render > Create Render Node > Maxwell Render command from the menu or using the Maxwell Render shelf.

During the rendering process the plug-in writes .mxs scene files per frame to the disc and calls Maxwell Render asynchronously to render the sequence. After the render is done the MPlay window is opened with the rendered images. Render channels (such as alpha, motion pass or depth buffer) are also read back to MPlay.

The node’s user interface consists of the basic ROP parameters (such as Render Control… and Start/End/Inc frame) and the Maxwell Render parameters which are separated to the following tabs:

• Settings
• Objects
• Channels
• Tone Mapping
• SimuLens
• Overlay Text
• IPR
• Scripts

Maxwell Render can also be started from the film wheel icon in the bottom left corner to render the actual viewport.

The operator interface follows the structure of the Maxwell Render application interface where it’s possible.

General Settings

The Settings tab contains global render and output parameters.

Scene

The following parameters are available to control the render process.

• Render Time: specifies the maximum time the render may run. There are two ways to stop a render in Maxwell Render: by setting a Sampling Level (level of quality) or by setting a Render Time (in minutes). If both parameters are set, the render will stop when one of them is reached. The longer the time, the cleaner and more accurate your image will be.
• Sampling Level: specifies the level of quality when the render should stop. Setting the Sampling Level is useful to ensure that all the frames of the sequence will reach the same quality level, regardless of the time needed for each specific frame. Higher sampling level will give a cleaner and more accurate image.
• Multilight: enables multilight control for intensity or color. Maxwell Render’s multilight feature enables users to adjust the intensity of all the individual or grouped lights in the scene interactively during or after the rendering process to get the required results. It’s possible to export all the emitters contribution to independent images (Separate), or saving only the composed render (Embedded).
  • Read back: if this option is set the multilight settings will be read after the render has finished and the values (such as sky intensity, emitter color, etc.) will be modified in the Houdini scene.
• CPU Threads: specifies the number of threads dedicated to the render. All available CPUs / Cores will be used by default. One core in a multi-core CPU is considered 1 CPU thread.
• Quality: specifies the quality of the render.
• Draft: low quality render with fast calculations.
• Production: high quality render.
• Command Line: specifies command line arguments when calling Maxwell Render. See the available command line parameters.

• Display dialog on error: pops up a dialog window on render errors when enabled.

• Camera: specifies the camera of the render. Render can not be started when there is no camera node added to the scene. If the Active Camera field is empty, the plug-in uses the first camera node from the scene.
• Motion Blur Steps: defines the number of iterations used to calculate transformation blur.
• Motion Blur: enables / disables motion blur calculations in the scene.

Options

Illumination and caustics settings are located on the Options tab. These controls are useful to deactivate certain aspects of the rendering calculations for compositing purposes.

• Displacement: enables / disables displacement calculations in the scene.
• Dispersion: enables / disables dispersion calculations in the scene.
• Direct Lighting: enables / disables direct lighting for illumination.
• Indirect Lighting: enables / disables indirect lighting for illumination.
• Direct Reflection Caustics: enables / disables direct reflection caustics.
• Indirect Reflection Caustics: enables / disables indirect reflection caustics.
• Direct Refraction Caustics: enables / disables direct refraction caustics.
• Indirect Refraction Caustics: enables / disables indirect refraction caustics.

Output

The following parameters specify render outputs.

• Output MXI: specifies the path of the .mxi file which will be generated by Maxwell Render.
• Output Image: specifies the path and the format with bit depth of the output image.
• Image Scale: scales the resolution of the output image. Resolution is defined by the camera, which is multiplied by this value.
• Show In MPlay: enables / disables opening the rendered image in MPlay.
• Output Scene (MXS): specifies the path of the output .mxs scene file which is passed to Maxwell Render. Use the Export button to export the .mxs file without starting Maxwell Render.
• Global Scale: specifies the scale of the translation.

• Export MXS files (no render): writes out Maxwell scene (mxs) files without starting the render.

Render Zone

This feature allows you to define an area of your image that will be rendered to a higher Sampling Level than the general frame, helping to distribute the rendering effort in those areas you consider that need more time. Find more information about the Extra Sampling feature here.

• Zone: enables/disables extra sampling.
• Mask: defines mask (area) of the extra sampling render.
  • Region: renders the region specified by the render camera.
  • Image: renders area covered by the given image.
  • Custom Alpha: renders zone covered by a custom alpha channel.
  • Alpha: renders zone covered by alpha channel.
• Sampling Level: specifies sampling level of the render.
• Custom Alpha: specifies the name of the custom alpha channel for Custom Alpha mask based render.
• Image: specifies the image for Image maks based render.
• Invert Mask: renders zone outside of the specified mask.

Objects

The objects tab defines which geometries and lights are translated to Maxwell from the scene. The fields are similar to the Mantra renderer.

• Candidate Objects: geometry objects in this parameter will be translated to Maxwell Render if their display flags are turned on.
• Force Objects: geometry objects in this parameter will be translated to Maxwell Render regardless of the state of their display flag.
• Exclude Objects: geometry objects in this parameter will be excluded from the scene regardless of whether they are selected in the Candidate Objects or Force Objects field.
• Solo Light: only lights in this parameter will be translated to Maxwell Render. If this parameter is set, the candidate, forced, and exclusion parameters are ignored.
• Candidate Lights: each light in this parameter will be translated to Maxwell Render if their display flags are turned on.
• Force Lights: each light in this parameter will be translated to Maxwell Render regardless of the state of their display flag.
• Exclude Lights: each light in this parameter will be excluded from the scene regardless of whether they are selected in the Candidate Lights or Force Lights field.

Channels

Several render channels are available in Maxwell Render which are useful for compositing tasks. This tab contains settings for the different channels used.

• Channels: specifies the way how the channels are exported:
• Separated: as independent files
• Embedded: as one single file. The Alpha channel can be embedded in the tga, png, tiff and exr formats.
  
  
• Render: the main render image. The following render types are allowed:
• Diffuse + Reflections: outputs the whole render including the diffuse and reflections (complete render).
• Diffuse: outputs only the diffuse color of the surfaces.
• Reflection: outputs only the reflective component of the surfaces.
• Alpha: enables / disables the alpha channel. The alpha channel is a black & white image which is reserved for transparency information.
  • Opaque: if this option is unchecked, transparent materials will render with a transparent alpha.
• Z-buffer: outputs an image representing the scene depth.
  • Range: specifies the range of the depth in meters (from the camera to the farthest object)
• Shadow: enables / disables shadow channel. Shadow channel is a grayscale image that represents the shadows received by objects that have a material applied to them with the “Shadow” option turned on.
• Material ID: outputs multicolored material silhouettes.
• Object ID: outputs multicolored object silhouettes.
• Motion Vector: outputs the x,y,z translation of each pixel. Useful to apply motion blur in compositing as a post process.
• Roughness: outputs an image containing the roughness value of the materials in the scene. High Roughness materials will appear white in the image, while low Roughness materials will appear dark.
• Fresnel: outputs an image containing the Fresnel information of the surfaces.
• Normals: outputs an image containing normals of the surfaces. Normals can be displayed in world or camera space.

• Position: outputs an image containing position information of the surface points. Position can be displayed in world or camera space.

• Deep: outputs a deep image format, which stores the depth information per pixel. You can save the whole RGBA channels with deep information or just the Alpha channel.

  • Min Distance: closer distance to the camera for taking the first depth sample.

  • Max Samples: number of depth information samples stored per pixel.

• UV:  outputs an image containing the information of the UV coordinates from the objects.

• Custom Alpha: generates an individual pure black&white alpha mask per user defined individual objects. An object can be assigned to custom alpha channels with the Maxwell Object Parameters node (see Camera and object parameters).

Selected render channels are displayed in MPlay together with the main render channel.

Custom Alpha

Custom alpha channels can be defined and assigned to any objects or materials on this tab. More details...

• Number of Channels: specifies the number of custom alpha channels in the scene. The following options will appear for each channel:
  • Name: name of the custom alpha channel.
  • Objects: list of object this channel is assigned to.
  • Materials: list of materials this channel is assigned to.

Tone mapping

This tab contains settings for the dynamic range of the image.

• Color Space: specifies color space for the rendered image.
• Temperature (K) / Tint: together they form the white balance tool in Maxwell. Please see the Camera white balance page for details.
• Burn: controls the highlights in a render. Lower burn values will decrease the intensity of the highlights to avoid “burned out” areas in the image.
• Monitor Gamma: controls the gamma conversion. Lower gamma values darken the image, higher values lighten the image.
• Sharpness: controls antialiasing filterings. In most of the situations the default value should work fine.

SimuLens

The SimuLens™ system mimics certain optical effects found in all camera lenses adding more realism to the render.

• Aperture Map: specifies the shape of the diaphragm which models the pattern of light that reaches the film. For example, a circular diaphragm will create circular patterns, a hexagonal diaphragm will create 6 light streaks. The aperture map should be black with white specifying the shape and size of the aperture.
• Obstacle Map: a black & white map to control diffraction effects. Aperture map is required to use the obstacle map. The two maps must have the same resolution. The obstacle map should be white with black areas specifying dirt or scratches on the lens surface.
• Diffraction: controls diffraction / glare intensity.
• Frequency: controls the frequency of coloring in the diffraction effect. Higher values will make the patterns denser.
• Scattering: specifies the instensity of scattering, commonly known as bloom.
• Devignetting: Vignetting is an artifact that darkens an image around the edges due to camera optics. The Devignetting slider removes the vignetting effect partially or completely by dragging it from 0 to 100%. In the real world, the more wide-angle the lens is (for example, a focal length of 24mm), the more pronounced the vignetting will be.

Overlay Text

You can display an overlay text in the rendered image using the following settings.

• Text: the text to be drawn if enabled.

• Font: specifies the font used to display the text.

• Position: specifies the position of the text in the image (top or bottom).

• Color: specifies the color of the text.

• Background: fills the background of the overlay with the specified color if enabled.

IPR

The Maxwell Render output driver is integrated with the Fire engine which provides Interactive Preview Render. The following parameters are control the quality of the render in interactive mode.

• Sampling Level: specifies the maximum sampling level required. The render will stop when this sampling level is reached.
• Time: specifies the maximum render time for the render in minutes.
• Size: specifies the size of the IPR output image relative to the render output resolution.
• Motion Blur: enables motion blur calculation in the interactive render (FIRE).
• Floating Shadows / Floating Reflections: enables displaying floating shadows and reflections of your objects on the ground. With this feature it is easy to show an object over a solid color background while producing reflections and shadows in the ground.

Scripts

User defined scripts can be added before and after the render process on the Scripts tab. This can be practical to execute automated operations such as file manipulations, etc.

• Pre-Render Script: defines a hscript or python script which will be run before the render starts.
• Post-Render Script: defines a hscript or python script which will be run after the render has been finished.
• Pre-Export Script: defines a hscript or python script which will be run before exporting to MXS.
• Post-Export Script: defines a hscript or python script which will be run after MXS export has been finished.