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Light linker pane

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Note

In Houdini 13 and later, use of the light linker is discouraged in favor of the light bank.

Overview

The light linker lets you manage links between various nodes.

The light linker lets you link lights to objects to control which lights illuminate which objects (Light Mask), which objects cast shadows from which lights (Shadow Mask), and which objects are reflected in other objects (Reflection Mask).

You can work by choosing which objects are lit by a light (Light-Centric), or by choosing which lights light an object (Object-Centric). For reflections, you can choose Reflector-Centric or Reflection-Centric.

The pane consists of two subpanes the contents of which are determined by the Link type and Mode settings. Each of these subpanes contains a hierarchical display of nodes, groups and bundles . Links are created by first selecting one or more items in the left (source) subpane and then selecting one or more items in the right (target) subpane.

How to

By default, all lights cast light on all objects, and all objects cast shadows from all lights (if they have shadows turned on). However, this is often not what you want, either because it’s inefficient, or because you want to use common but technically non-realistic techniques such as character-specific lights.

You can use light linking to set up specific relationships, so that an object only receives light from certain lights, and/or only casts shadows from certain lights.

You can link lights and shadows interactively using the Light Linker pane, individually for each object and light directly in the parameter editor, or by specifying categories.

To...Do this

Open the light linker pane

Click the new tab icon in the network editor and selecting New Pane Tab Type ▸ Light Linker. You can also change an existing pane to a light linker pane by clicking on an existing pane and choosing Light Linker.

Illuminate objects

  1. Choose Light Mask from the Link Type drop-down menu.

  2. Choose a mode from the Mode drop-down menu.

  3. Select the lights from the Light Sources pane.

  4. Select the objects to light from the Lit Objects pane.

or

On the Render tab of an object, set the Light Mask on the Shading sub-tab in the parameter editor to determine which lights will illuminate your object.

Cast shadows from objects

  1. Choose Shadow Mask from the Link Type drop-down menu.

  2. Choose a mode from the Mode drop-down menu.

  3. Select the lights from the Light Sources pane.

  4. Select the objects which will cast shadows from the Shadow Casters pane.

or

On the Shadows tab of a light, choose the Shadow Type from the drop-down menu (The default is No Shadows). Set the Shadow Mask to determine which objects will cast shadows from your light.

Reflect objects in other objects

  1. Choose Reflection Mask from the Link Type drop-down menu.

  2. Choose a mode from the Mode drop-down menu.

  3. Select the objects that are reflected from the Reflection Sources pane.

  4. Select the objects to reflect from the Reflector Objects pane.

or

On the Render tab of an object, set the Reflection Mask on the Shading tab in the parameter editor to determine which objects will be reflected by your object.

Set up the link editor

  1. Choose the Link type and Mode.

  2. You can optionally filter the items using the Filter field.

Link source items to target items

  • Choose the source of the link in the left subpane. The right subpane shows all possible link targets, with the currently linked items highlighted. Select items in the right subpane to link them to the source item in left subpane.

    The link editor always reflects the current state of the scene file. Linked items are blue in the target list. Partially linked items are white.

  • Use the Select field to control which items are selected in the target list with a pattern. Enter a pattern in the field and click + to add select any matches, - to deselect any matches, or = to select only the matches.

    The @bundle_name pattern will match the contents of a bundle , not the bundle itself. To match the bundle, use @@bundle_name instead.

See the parameter values being controlled by the link

  • Move the mouse over the appropriate sub-pane, press ((Ctrl + RMB)) and choose Show Spreadsheet, or press W. Only the subpane whose items contain the parameter being affected can show this spreadsheet. This will be the subpane displaying the lit objects when light masking, light sources when shadow masking, and reflector objects when reflection masking.

Tip

A quick way to add a node to a group or bundle is to drag it onto the corresponding tree node.

Tip

The cells in the spreadsheet column can be edited and multiple cells can be selected by holding Space and either clicking or dragging.

Tip

Channel references are followed when setting mask parameters making it possible to link objects embedded in locked assets.

Toolbar buttons

Export view camera (camera icon)

When this button is on, when you select a light in the source tree, the 3D viewer will automatically look down the light.

Read-only target selection (lock icon)

When this button is on, you cannot select or deselect link targets.

Select toolbar

Sets the selection to items that match the value in the Select field.

Adds items that match the value in the Select field to the current selection.

Removes items that match the value in the Select field from the current selection.

Pane menu entries

Linker

Read-only target selection

When this button is on, you cannot select or deselect link targets.

Export source as view camera

When this button is on, when you select a light in the source tree, the 3D viewer will automatically look down the light.

View

Source tree spreadsheet

When this toggle is on, the left subpane will contain a column displaying the parameters being modified (if appropriate).

Target tree spreadsheet

When this toggle is on, the right subpane will contain a column displaying the parameters being modified (if appropriate).

Expose linked target nodes

When this toggle is on, selecting items in the left subpane will cause the currently linked items in the right subpane to be exposed, expanding parent items as necessary.

Troubleshooting

I can’t select items in the target list

Possible causes and solutions:

  • The read-only button is on.

    Make sure the lock button above the right/target list is off (the button is bright yellow when it’s on).

  • The parent is a bundle or a group.

    You cannot individually link a member of a bundle or a group using the contents of that bundle or group in the tree. This is by design. You will need to find the node in the operator hierarchy in order to link it.

I can’t see my group or bundle

  • The group or bundle is not empty, but contains no operators of the expected type. The linker will display empty groups or bundles to allow linking before populating them. However, once a group or bundle is non-empty, the linker attempts to reduce the clutter in the subpanes.

    Either add an operator of the expected type to the group or bundle, or create a new one.

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