Houdini 17.0 Nodes Render nodes

OpenGL render node

Render an image using the hardware-accelerated 3D viewport renderer.

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The OpenGL output operator renders the scene using the graphics hardware present on the system. It uses the 3D viewport renderer, but without rendering any handles, guides or other decorations. A limited set of display options is provided as parameters. This operator can be used in non-graphical applications, such as hbatch or hython.

Note

A GL3.3-capable graphics device must be present on the system in order to render from this output driver.

Parameters

Render

Begins the render with the last render control settings.

Render Control

Opens the render control dialog to allow adjustments of the render parameters before rendering.

Valid Frame Range

Controls whether this render node outputs the current frame (Render any frame) or the image sequence specified in the Start/End/Inc parameters (Render Frame Range).

Render Frame Range (strict) will render frames start to end when it is rendered, but will not allow frames outside this range to be rendered at all. Render Frame Range will allow outside frames to be rendered. This is used in conjunction with render dependencies. It also affects the behavior of the Output Override for Frame Range in the Render Control dialog.

Two possible cases where you would want strict behavior:

  • A 60 frame walk cycle written out to a geo, but part of a larger ROP net to render out a larger frame range.

  • A texture loop from 1-20.

Otherwise, you will usually set this to non-strict.

Render Current 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.

Render With Take

The output driver will switch to this take before rendering and then restore the current take when rendering is done. Choose Current to use the current take when rendering.

Tip

Use chs("take") to use this value in other parameters. See the chs expression function for more information.

Scene

Camera

The camera object which defines the scene.

Scene Path

The root path for the scene. All objects and lights in this object network will be rendered.

SOP Source

Which geometry to render in the object, either the SOP with the display or the render flag set.

Candidate Objects

Specifies which objects will be rendered in the scene, if their display flags are also set. The paths can be absolute (\/obj\/geo1) or relative to the scene path (geo1, with a scene path of \/obj). Wildcards can be used (\*, ?), as can the exclusion operator (^). \* \^geo? would render all objects except for those like geo1, geo2, geoN.

Force Objects

Specifies that the objects that match the names or patterns of this parameter should always appear in the scene, even if their display flag is off.

Note

This overrides the Candidate Objects and Exclude Objects parameters.

Exclude Objects

Do not include objects in the scene if they match the names or patterns given by this parameter. This overrides both Candidate and Force Objects.

Candidate Lights

Specifies which lights will be used to light the scene, if they are enabled. The same rules apply to the light mask as

Force Lights

The lights matching the names or patterns of this parameter will always be included, even if they are disabled.

Exclude Lights

Do not include lights in the scene if they match the names or patterns given by this parameter. This overrides both Candidate and Force Lights.

Initialize Simulation OPs

Forces all simulation OPs to be reset. This includes DOP Networks, POP SOPs, and other OPs that cache their results.

Show in Viewport Menu

When enabled, this ROP will appear in the viewport’s render menu.

Override Camera Resolution

Normally, the resolution channels on the camera determine the output resolution. Enabling this parameter allows an alternate resolution to be used.

Resolution

Allows you to override the camera resolution.

Pixel Aspect Ratio

The pixel aspect ratio represents the width of a pixel divided by the height of a pixel. It is not the aspect ratio of the image (which is determined by the resolution of the image). This parameter does not affect rendering, it is only used to change how images are displayed, by stretching the pixels by this factor.

Background Image

Specifies a background image to use, either a file or a COP node reference with op:. The background image is fit to the viewport area if the aspect ratios or size don’t match.

Viewport Comment

Places a comment in the upper left corner of the image, in addition to any viewport comment on the camera.

Output

Output Image

The image or device where the resulting image will be rendered. You can set this value to ip which renders the image in MPlay, or you can save it to an image. The following image types are supported: .pic, .tif, .sgi, .pic.gz, .rat, .jpg, .cin, .rta, .bmp, .tga, .rad, .exr, and .png.

Include $F in the file name to insert the frame number. This is necessary when rendering animation. See expressions in file names for more information.

Image Format

The image format or device for the output image. If you leave this at the default value of Infer from filename, the image format will be selected based on the file extension (eg. .pic will automatically generate a Houdini format image).

The options inside the box that follows are image format-specific.

Create Intermediate Directories

Create intermediate parent directories for output files as needed. This currently only applies to generated scripts, images, and shadow maps.

Save Retries

The number of times the image save will be attempted again before it reports that the save failed.

Image Type

The type of image to render:

Color Image

Regular 2D RGBA image of the color beauty pass (RGBA).

Depth Image

2D depth image, with depth in camera space (fp32 single channel).

360' Cube map

360 degree render of the beauty pass to a cube map (RGBA).

Color Correction

Style of color correction to apply to the output image.

None

No color correction, leave in linear colorspace.

LUT and Gamma

Apply a LUT (lookup table) file and a gamma correction.

OpenColorIO

Optionally apply OpenColorIO looks and convert to the specified colorspace from linear colorspace.

Gamma

Applies gamma correction to output image. This should usually be left at 1.0.

Display LUT

Applies a LookUp Table (LUT) to the output image, after gamma is applied.

OCIO Colorspace

The OpenColorIO colorspace to transform the linear colors produced by the OpenGL render. If empty, leave as linear.

OCIO Looks

A optional, whitespace separated list of OpenColorIO looks to apply to the color data before converting to the specified colorspace.

Display Options

Note

The capabilities of the graphics hardware and driver may cause some of these options to be disabled.

Antialias

Enables high-quality rendering by smoothing jagged edges of lines and polygons. Increasing this setting will proportionately increase the amount of framebuffer memory used. 4× and 8× modes should only be used if the graphics memory installed on the graphics card is 1GiB or higher.

High Dynamic Range

Enables High Dynamic Range (HDR) rendering which produces higher quality results for volumes and transparency. It can also be used in conjunction with a LUT to view superwhite values. If enabled, 16b or 32b floating point HDR images are rendered. Enabling this option doubles or quadruples the framebuffer size.

Off

Render using normal dynamic range, black to white, to a 8b framebuffer.

HDR (16b FP)

Full HDR (32b FP)

Stereo Mode

When the Camera is a stereo camera, this determines the type of output image(s).

Anaglyph

A red/cyan anaglyph image is produced, for use with red/cyan glasses.

Separate Left/Right Images

Two images are produced for each frame, one for the left eye and the other for the right.

Left/Right

The images for the left and right eyes are placed side by side in the same image, left eye on the left.

Right/Left

The images for the left and right eyes are placed side by side in the same image, left eye on the right.

Over (L)/Under (R)

The images for the left and right eyes are placed one above the other in the same image, left eye on the top.

Over (R)/Under (L)

The images for the left and right eyes are placed one above the other in the same image, left eye on the bottom.

Shading Mode

Select a shading mode for all geometry in the scene.

Display Textures

Materials will include textures if enabled.

High Quality Light Shading

Area and environment lights are rendered with more accurate representations. Spotlight falloff and ramp-based attenuation are also incorporated into the shading. This mode attempts to closely match the results seen in mantra at the expense of performance.

Note

This may disable Antialiasing if the graphics hardware does not support certain OpenGL features.

This shading does not apply to transparent objects if Transparency is enabled. Normal shading is used instead. Additionally, this feature requires Material Shaders.

Light Sampling

The number of samples to use when rendering area and environment lights in High Quality Light Shading mode. It is ignored when this mode is not active. Higher numbers produce more accurate results, at a slight performance hit.

Shadows

Enables light shadowing from those lights which have their Shadow Type parameter set to a shadowing method. This option decreases performance and increases graphics memory use but greatly improves the quality of the viewport display.

Tip

The light’s shadow map(s) are re-calculated when its position, orientation or projection changes. You may want to disable shadows while editing a light to improve interactivity.

Increasing the shadow quality will improve the shadow’s visualization, especially for area and environment lights, with a corresponding performance decrease.

Point

All lights are shadowed as if they were point lights, producing hard shadow edges. This is the lowest quality setting.

Antialiased Point

Improve the shadow edges by softening jagged edges caused by light map aliasing.

Area

Area lights use many shadow maps to produce a soft shadow effect. Environment lights perform more sampling. This has no effect on other light types (point will be used in these cases). Moving an area light with this option on will result in slower interactivity.

Antialiased Area

Soften the jagged edges of shadows, which improves the soft shadow look.

Shadow Map Size

Controls the resolution of the shadow maps. Increasing the shadow map size will reduce the jaggedness of shadow edges and improve fine shadow detail. Larger maps may affect performance and will use more graphics memory.

Ambient Occlusion

Enable screen-space ambient occlusion, which shadows objects based on the amount of ambient light that could reach a surface. Areas in corners and sunken areas will receive shadowing. The numeric value increases the quality and range of effect of the occlusion. Enabling this option will slow performance somewhat. High Quality Light Shading and Material Shaders are required for occlusion to work.

Note

The HIP file’s Unit Length parameter affects how far away the shadowing effect extended.

Transparency

Draw objects with per-pixel alpha, texture maps with alpha or material transparency using alpha blending (via an over operation). When off, pixels with non-zero alpha are drawn and zero alpha pixels are discarded. The quality of the transparency can also be selected, with the higher quality options impacting performance.

Low

Transparent objects are only sorted by object order. Overlapping surfaces within an object may be rendered incorrectly, unless objects are sorted manually in the scene hierarchy list or a Sort SOP is used at the end of the object’s geometry chain.

Medium

Transparent objects are sorted per-pixel, producing a more realistic display of complex transparent objects.

High

Transparent objects are sorted per-pixel and are shadowed, if shadows are enabled. More render passes are used to resolve transparent layering issues, if they are needed.

Note

Medium and High transparency modes require Material Shaders.

Depth of Field

Enable depth of field effect, based on the camera’s f-stop, aperture, and focus distance. This is done by rendering the scene multiple times while jittering the camera. When enabled, the parameter specifies the number of times the camera is jittered. Higher values produce a better quality image, at the expense of a longer render time.

Motion Blur

Enable a motion blur effect, based on the camera’s shutter. The scene is rendered at multiple subframes around the current frame and blended. When enabled, the parameter specifies the number of subframes to render. Increasing the number of subframes improves the image quality, at the expense of a longer render time.

Displacement

Enable displacement mapping for those materials with a GL Displacement Map parameter. The slider field can be used to increase or decrease the tessellation factor of the displaced surface. OpenGL 4.0 is required for this feature.

Reflections

Enable reflections using reflection cubemaps. This simulates reflections by rendering the scene to a cubemap with the reflection object removed, at the reflective object’s centroid. Reflective objects are those with a material with a GL Reflect parameter that is greater than zero.

Min Reflection

Require that a material have a GL Reflect parameter set to at least this value, otherwise do not consider the material reflective. No reflection cubemaps are generated for objects with non-reflective materials. This can reduce the number of reflection maps generated for very dull materials.

HDR Reflections

Use a FP16 cubemap to store high-dynamic range reflections. When disabled, an 8b cubemap is used (standard 0-1 color range). HDR reflections look brighter, but use twice the texture memory.

Reflection Map Size

Resolution of the cubemap’s square images, in pixels. Larger maps produce sharper reflections at the expense of increased reflection map generation time and texture memory use.

Geometry

Volume Quality

Very Low

An axis-aligned volume is drawn, with volume slices parallel to one of the volume box’s faces. This is the fastest option but produces a visual pop as the volume is rotated in the view. Overlapping volumes will produce visual artifacts.

Low

A view-aligned volume is drawn, with volume slices drawn parallel to the viewport. This produces a higher quality visualization of the volume. Overlapping volumes will render correctly. The slices are widely spaced apart. This is the fastest of the view-aligned options, and is useful for working interactively with dozens of volumes.

Normal

A view-aligned volume is drawn, with volume slices packed more densely together. More slices are drawn so the overall render is slower than 'Low'. This option strikes a good balance between quality and performance.

High

A view-aligned volume is drawn with slices drawn very densely. This is the slowest but best quality rendering of volumes.

Tip

Enabling HDR Rendering will remove any banding artifacts from volumes.

Geometry LOD (Level of Detail)

Increases or decreases the display resolution of Metaballs, NURBS, and Bezier surfaces.

Wire Width

The width, in pixels, of wireframe and wire-over-shaded lines.

Wire Blend

The amount that wire-over-shaded lines are blended with the underlying shaded surface. Values near zero make these lines very faint, while a value of one draws the line without any blending (opaque). This does not affect pure wireframe, hidden line, or invisible line modes.

Particle

The particle representation to use:

Point

Draw particles as points, affected by the Point Size, in screen pixels. They are not affected by perspective.

Pixel

Each particle is a single pixel. This is useful for visualizing dense flip simulations.

Lines

Particles are drawn as streaks so it is possible to see their direction.

Discs

Draw particles as discs, affected by the Disc Size, in world units. They are affected by perspective.

Orient Discs to N

In particle disc mode, discs can be oriented to the direction of the normal (N) attribute on the particle. They will face the direction of the normal. Otherwise the discs are drawn screen-aligned so that they face the camera.

Use Sprites

Display sprites instead of the current Particle representation if a sprite attribute is found, such as spriteshop, spritescale or spriterot. If disabled, these attributes are ignored and the Particle representation is always used.

Use Geometry Color

When enabled, a Cd attribute on the geometry will be respected. It is ignored otherwise.

Limits

Warning

Greatly exceeding these limits can cause instability based on your graphics driver and OS platform. Windows in particular can reset the graphics driver if a single draw takes longer than 2 seconds.

Limit 2D Textures

Limit 2D Textures (images) to a maximum resolution in one of three ways. Textures are still subject to the Tex Mem Limit memory limitation for a single texture. If a texture exceeds this limit it will be uniformly downscaled to the limit.

OpenGL Limit

Textures are only limited by the maximum 2D texture resolution reported by OpenGL (usually 8192 or 16384).

Auto-Detected Limit

Texture size recommended by Houdini based on the amount of VRAM installed on the graphics hardware.

Specify Limit

Manually specify the limit using the Max 2D Resolution parameter.

Max 2D Resolution

Maximum allowable 2D texture width or height.

2D Texture Format

The maximum allowable bit depth for 2D textures. If a texture’s bit depth exceeds this limit, it will be downcast to the limiting bit depth. If a textures bit depth is less than the limit, it will remain unchanged (ie, not up-converted to the limit bit depth).

8b Fixed

Standard dynamic range (0..255) bit depth. Uses the least amount of memory but super-white values are clamped at white.

16b FP

High dynamic range bit depth with reasonable color resolution. A good memory vs. quality setting.

32b FP

Ultra high dynamic range bit depth. Uses twice as much memory as 16b FP and has an impact on texture filtering speed. Use with caution.

Limit 3D Textures

Limit 3D Textures (volumes) to a maximum resolution in one of three ways. Textures are still subject to the Tex Mem Limit memory limitation for a single texture. If a texture exceeds this limit it will be uniformly downscaled to meet the limit.

OpenGL Limit

Textures are only limited by the maximum 3D texture resolution reported by OpenGL (usually 2048 or 8192).

Auto-Detected Limit

Texture size recommended by Houdini based on the amount of VRAM installed on the graphics hardware.

Specify Limit

Manually specify the limit using the Max 3D Resolution parameter.

Max 3D Resolution

Maximum allowable 3D texture width or height.

3D Texture Format

The maximum allowable bit depth for 3D textures. If a texture’s bit depth exceeds this limit, it will be downcast to the limiting bit depth. If a textures bit depth is less than the limit, it will remain unchanged (ie, not up-converted to the limit bit depth).

8b Fixed

Standard dynamic range (0..255) bit depth. Uses the least amount of memory but super-white values are clamped at white. Not recommended for volume display.

16b FP

High dynamic range bit depth with reasonable color resolution. A good memory vs. quality setting.

32b FP

Ultra high dynamic range bit depth. Uses twice as much memory as 16b FP and has an impact on texture filtering speed. Use with caution.

Tex Mem Limit (MB)

The maximum allowable texture size for a single texture. If the computed texture size exceeds this limit it will be uniformly downscaled to meet this limit. This applies to both 2D and 3D textures, though it more frequently affects tiled textures (UVTile, UDIM). The total memory size of all textures can exceed this size - it only applies to large textures.

Max Sprite Resolution

The maximum allowable resolution for sprite textures. Sprites larger than this resolution will be downscaled to fit.

Instancing Percent

The percentage of instances shown when Point Instancing is enabled. Instances not shown will be replaced by the Instancing Standin geometry.

Instancing Limit (M)

The maximum number of polygons that can be generated when instancing, in millions of polygons. If a single Point Instancing operation exceeds this amount, some of the instances will be replaced by the Instancing Standin geometry.

Instancing Stand-in

Geometry to substitute for instances that are culled by either the Instancing Percent or Instancing Limit parameters.

None

Don’t show anything for culled instances.

Location Marker

Show a small marker for culled instances at their object position.

Bounding Box

Show a wireframe bounding box for culled instances.

Scripts

Each script parameter refers to an hscript command or python script which will be run. Each script parameter has a enable toggle as well as a language selection (hscript or python).

The scripts 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 rendering is started. It is only run once per render.

Pre-Frame Script

This command is run before each frame is rendered.

Post-Frame Script

This command is run after each frame is rendered.

Post-Render Script

This command is run one time, after all rendering is complete.

See also

Render nodes

  • Agent

    This output operator is used to write agent definition files.

  • Alembic

  • Archive Generator

    Generates disk-based archives which can be used by either mantra or RIB renderers.

  • Bake Animation

    Bakes animation from object transforms and CHOP overrides.

  • Bake Texture

    Generates a texture map from one or more objects' rendered appearance.

  • Batch

    Renders the input ROP in a single batch job.

  • Brick Map Generator

    Allows you to convert Houdini volume primitives into Pixar brickmap files.

  • Channel

    The Channel output operator generates clip files from a particular CHOP.

  • Composite

    The Composite output operator renders the image(s) produced in the Compositing Editor.

  • DSM Merge

    Merges two or more deep shadow/camera map files.

  • Dynamics

    Saves the state of a DOP network simulation into files.

  • Fetch

    Makes a dependency link to a ROP in a different network.

  • Filmbox FBX

    Exports entire scenes to FBX files.

  • Frame Container

    Prevents frame dependency changes in the contained nodes from affecting its inputs.

  • Frame Depedency

    Allows an output frame to depend on one or more input frames.

  • Geometry

    Generates geometry files from a SOP or DOP network.

  • HQueue Render

    HQueue, or Houdini Queue, is a distributed job scheduling system.

  • HQueue Simulation

    HQueue, or Houdini Queue, is a distributed job scheduling system.

  • Hair Card Texture

    Renders hair textures for use on hair cards.

  • MDD Point Cache

    This output operator is used to write an MDD animation file.

  • Mantra

    Renders the scene using Houdini’s standard mantra renderer and generates IFD files.

  • Mantra Archive

    Generates disk-based archives which can be used by mantra.

  • Merge

    Merges several render dependencies into one.

  • Net Barrier

    Blocks the ROP network until synchronization occurs.

  • Null

    Does nothing.

  • OpenGL

    Render an image using the hardware-accelerated 3D viewport renderer.

  • Pre Post

    Renders ROPs before and after a main job.

  • RenderMan

    Renders the scene using Pixar’s RenderMan renderer.

  • RenderMan

    Renders the scene using Pixar’s RenderMan RIS renderer.

  • RenderMan Archive

    Generates disk-based archives which can be used by RenderMan .

  • Shell

    Runs an external command.

  • Subnetwork

    The SubNetwork output operator provides an easy way to manage large number of output operators.

  • Switch

    Renders one of several inputs.

  • Tractor

    Tractor is a program shipped out with Pixar’s distribution of RenderMan.

  • Wedge

    Re-renders the same ROP multiple times with different settings

  • Wren

    This output operator is used to drive the Wren rendering program.

  • glTF

  • glTF