The Decay Light Filter provides control over the light decay with many more parameters other than the decay rate.
Creating a Decay Light Filter
To create a decay light filter, right-click in the GafferThree's Object table and select Add → Decay Light Filter, or press the B key. Decay light filters are not shown in the Viewer, but they do offer a Decay Filter Manipulator in the Viewer, which is explained in a following section.
A decay filter in the GafferThree node parameters.
Applying a Decay Light Filter to a Light
Decay filters can be applied on area lights, distant lights, spot lights and point lights.
In order to apply a filter to a light, it must be set as a child of that light. Alternately, a light filter reference can be put in place as a light child; it will act as a filter proxy. To set the filter as the light child, simply middle-click and drag the light filter on the light, in the Gaffer Object Table. To use a light filter reference as a proxy: Using a light filter reference allows sharing one filter with several light sources.Alt+F;
Controlling a Decay Light Filter
Interactively editing Decay Filter Controls in the Viewer
To enable the Decay Filter Manipulator, select a decay light filter in the Scene graph or the Viewer. It will unlock a Manipulators → Decay Filter menu item in the Viewer. Choose this menu item or press the Tab key to display the decay filter manipulator.
Displaying the manipulator will also fill the Quick Editor with the decay filter parameters. The Quick Editor can be displayed by choosing Layout → Show Quick Editor, by pressing the A key, or by dragging the right edge of the Viewer to the left.
The decay filter manipulator offers controls on the Decay Range Start and Decay Range End parameters. Drag the manipulator boxes to edit values. The filter parameters are detailed in the next sections.
Decay Light Filter Controls
The Material tab contains several parameters which are explained in the following sections.
The Material tab of a decay light filter.
Decay Type
Specify on what variable the decay is evaluated. Available options are:
| Value | Description |
|---|---|
| Distance from light | Decay curve sections define radial regions from the light source. |
| Distance from light plane | Decay curve sections define regions perpendicular to the light source's emitting plane. |
Angle from axis | Decay curve sections define angle ranges from the light's axis. A given curve section will define a wider light region when placed toward the right end of the decay curve. |
| Distance from axis | Decay curve sections define distances from the light's axis. |
Decay Range Start
Decay Range End
This pair of parameters defines the range of distances (or angles when Decay Type is set to 'Angle from Axis') over which the decay curve is applied.
Decay Curve
Defines the decay values over the range specified by Decay Range Start & End. The curve gadget is very similar to the Curve Editor:
Points can be added with a CTRL + ALT + left mouse click, or by toggling on the point insertion mode by pressing the Insert keyboard key; each mouse click will then add a point. Press the ESC key to exit insertion mode.
Points can be deleted by selecting them and pressing the Delete keyboard key.
Position
The position of the currently selected curve point.
Value
The value of the currently selected curve point.
Interpolation mode
How values are interpolated between curve points. Available interpolation modes are:
| Value |
|---|
| catmull-rom |
| bspline |
| linear |
| constant |
Presets
A list of predefined curves. Available presets are:
| Value | Description |
|---|---|
| Constant Min | A flat curve set at 0. |
| Constant Max | A flat curve set to 1. |
| Linear Min to Max | A straight line from 0 to 1. |
| Linear Max to Min | A straight line from 1 to 0. |
| Smooth Min to Max | A S-curve from 0 to 1. The lower and higher end values progress more slowly than the middle portion. |
| Smooth Max to Min | A S-curve from 1 to 0. The higher and lower end values progress more slowly than the middle portion. |
| Cut-On-Cut-Off | The curve starts and ends at 0, and is set to 1 for the middle 80% of the range and sharp S-curves for the transitions. |
| Cut-Off-Cut-On | The curve starts and ends at 1, and is set to 0 for the middle 80% of the range and sharp S-curves for the transitions. |