View Full Version : Spotlight shadow problem...

10-22-2004, 07:53 PM
I don't know if it means anything to anyone but I was playing around with Lightwave and I noticed that spotlights when on shadow mapped shadows does not take any transparency into account when rendering. I don't know if anyone else has noticed it, but if you have and know I am missing something please do tell so.

I basically just set up a simple polygon as a plane, and another two-segmented flat square blocking part of a spotlight from hitting the plane. One segment of the blocking square has 50% transparency while the other has none. When the spotlight is set to Ray Trace shadows all goes well; halve of the shadow is grayish due to transparency and the other halve is fully black (light's shadow color is set to black). But when I switch on Shadow Map the shadow is fully black. I usually use Area Lights (I tested area lights and they don't have this problem) but I might use Spotlights in the near future due to rendering times and I was wondering if there is a way around this and if not I just wanted to let people know (unless everyone already knew, sorry about that).

Thank you.

10-22-2004, 10:22 PM
It's not a bug -- when you use shadow maps you need to accept some limitations. If you need realistic shadows involving transparency, you have to use ray tracing. Shadow maps are great for opaque objects, plus they are faster and you can set the edge blurryness. But if you need to cast a shadow from a semi-transparent object, shadow maps don't work.