[X3D-Public] Why X3D 3.3 changes the default values of beamWidth and cutOffAngle

Michalis Kamburelis michalis.kambi at gmail.com
Sat Jan 21 18:22:50 PST 2012


I was looking at the draft of X3D 3.3 specification, and noticed a 
change to the default SpotLight.beamWidth and cutOffAngle. Looks like in 
X3D 3.3:

- cutOffAngle is by default pi/2
- beamWidth is by default pi/4

In X3D 3.2 and earlier, it was the other way around,

- cutOffAngle by default pi/4
- beamWidth by default pi/2

This is a very bad change in my opinion...

1. It breaks compatibility for no good reason. Suddenly by changing 
version number from 3.2 to 3.3 on your X3D scene, you will have 
SpotLights with larger size (cutOffAngle) and smooth borders. (Unless 
you specified angles explicitly in the file, of course.)

2. The defaults in X3D 3.2 were also much safer and faster. When 
beamWidth is > cutOffAngle, you have a light without a falloff (constant 
intensity within light cone). This is implementable using fixed-function 
OpenGL spot lights. Cases when beamWidth is < cutOffAngle are not 
precisely implementable using standard OpenGL spot lights with 
fixed-function pipeline.

I hope that this is just a typo in X3D 3.3 draft, and it's going to be 
corrected :)

For reference:
- X3D 3.3 about lighting component: 
- X3D 3.2 lighting component SpotLight: 


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