vtkLightKit

Section: Visualization Toolkit Rendering Classes

Usage

vtkLightKit is designed to make general purpose lighting of vtk scenes simple, flexible, and attractive (or at least not horribly ugly without significant effort). Use a LightKit when you want more control over your lighting than you can get with the default vtk light, which is a headlight located at the camera. (HeadLights are very simple to use, but they don't show the shape of objects very well, don't give a good sense of "up" and "down", and don't evenly light the object.)

A LightKit consists of three lights, a key light, a fill light, and a headlight. The main light is the key light. It is usually positioned so that it appears like an overhead light (like the sun, or a ceiling light). It is generally positioned to shine down on the scene from about a 45 degree angle vertically and at least a little offset side to side. The key light usually at least about twice as bright as the total of all other lights in the scene to provide good modeling of object features. The other lights in the kit (the fill light, headlight, and a pair of back lights) are weaker sources that provide extra illumination to fill in the spots that the key light misses. The fill light is usually positioned across from or opposite from the key light (though still on the same side of the object as the camera) in order to simulate diffuse reflections from other objects in the scene. The headlight, always located at the position of the camera, reduces the contrast between areas lit by the key and fill light. The two back lights, one on the left of the object as seen from the observer and one on the right, fill on the high-contrast areas behind the object. To enforce the relationship between the different lights, the intensity of the fill, back and headlights are set as a ratio to the key light brightness. Thus, the brightness of all the lights in the scene can be changed by changing the key light intensity.

All lights are directional lights (infinitely far away with no falloff). Lights move with the camera.

For simplicity, the position of lights in the LightKit can only be specified using angles: the elevation (latitude) and azimuth (longitude) of each light with respect to the camera, expressed in degrees. (Lights always shine on the camera's lookat point.) For example, a light at (elevation=0, azimuth=0) is located at the camera (a headlight). A light at (elevation=90, azimuth=0) is above the lookat point, shining down. Negative azimuth values move the lights clockwise as seen above, positive values counter-clockwise. So, a light at (elevation=45, azimuth=-20) is above and in front of the object and shining slightly from the left side.

vtkLightKit limits the colors that can be assigned to any light to those of incandescent sources such as light bulbs and sunlight. It defines a special color spectrum called "warmth" from which light colors can be chosen, where 0 is cold blue, 0.5 is neutral white, and 1 is deep sunset red. Colors close to 0.5 are "cool whites" and "warm whites," respectively.

Since colors far from white on the warmth scale appear less bright, key-to-fill and key-to-headlight ratios are skewed by key, fill, and headlight colors. If the flag MaintainLuminance is set, vtkLightKit will attempt to compensate for these perceptual differences by increasing the brightness of more saturated colors.

A LightKit is not explicitly part of the vtk pipeline. Rather, it is a composite object that controls the behavior of lights using a unified user interface. Every time a parameter of vtkLightKit is adjusted, the properties of its lights are modified.

.SECTION Credits vtkLightKit was originally written and contributed to vtk by Michael Halle (mhalle@bwh.harvard.edu) at the Surgical Planning Lab, Brigham and Women's Hospital.

To create an instance of class vtkLightKit, simply invoke its constructor as follows

  obj = vtkLightKit

Methods

The class vtkLightKit has several methods that can be used. They are listed below. Note that the documentation is translated automatically from the VTK sources, and may not be completely intelligible. When in doubt, consult the VTK website. In the methods listed below, obj is an instance of the vtkLightKit class.