Lens flare shader how to create a virtual radius area lights
Article needs peer review
Summary
The source of any Point or Spot light that is not an Area light is an absolute point. Consequently, it is not possible to render the light (and it's flare) as being partially obstructed when an object passes between it and the camera - either the light is visible or it isn't.
In SOFTIMAGE|3D, one would use the Virtual Radius option to gradate between the light's on and of status', interpolating the effect over a range of frames, and thus achieving a realistic eclipse type of light play. In SOFTIMAGE|XSI version 1.0, the Virtual Radius option is no longer available for the Lens Flare shaders.
Steps
The Virtual Radius option became a redundant with the introduction of Area Lights. The user defines the size of the Area Light and applies it to the light source itself (i.e. the shader).
TIP: You can make an Area Light Exclusive and use it simply to create flares; it's color can be tuned to achieve
the desired visual effect without affecting the scene's illumination whatsoever.
More Information
"But don't Area Lights increase render time?"
This is a generalization that certainly does not apply to this scenario.
It is true that, contrary to a standard Point or Spot light, an Area Light has to be sampled multiple times, once for every point on each surface it illuminates. The higher the number points on the surface, the more complex the computation ...and the longer the rendering time.
However, if the Area Light is simply being used to create flares, then only one sampling takes place, the one required to determine how much light is reaching the camera.
References
Online Documents
Shaders, Lights & Cameras guide:
Working with Lights and Blurs, Flares & Other Effects chapters
Knowledge Base articles
<A href="article.asp?ID=197">Associate Objects to an Inclusive/Exclusive light</A>
Applies To: XSI 1.0,XSI 1.5 on NT,Win2K,Irix
Posted: 10/12/2000
