View Full Version : shadowmaps don't like transparancy

07-12-2007, 10:23 AM
I have a nice medical animation scene built with pretty soft shadows cast by about 10 spot lights. The problem occurs when I dissolve away the skin to expose the muscles, then again when I dissolve away the muscles to show the bones and ligaments. When the skin is just partially transparent, everything beneath is murky dark. Then at the 99-100% transparent threshold, BOINK!, pretty and bright muscles. I hope my description is clear.

I just did a keyword search and found 4 year old posts that explain that shadowmaps don't like transparancy. Is this still true in version 9.0? Is my best option to change my lights to area lights? Because, personally, I don't like the sharp crisp shadows of raytrace. Does anyone remember the old trick of spinning a distant light (raytrace shadow) at a thousand rpm to make it have a soft shadow. Does that still work? I don't remember exactly how that was done.

Well, hopefully someone will have a cleaver work around for this! You guys and gals rock!

07-12-2007, 10:52 AM
It is still strue.
The easiest way... render two scenes, one with one without the muscles and one with them - fade in post/editing.


07-12-2007, 02:33 PM
Thanks, Mike Lightwolf,
I was afraid that would be the answer. I have a number of things fading in and out- skin layers, muscles, ligaments, veins, arteries, nerves, lymphs, plus certain things dissolving to 30% so you can still see them, but to see thru them for placement reference. All the time, the camera is moving thru the scene. That is a lot of renderings to keep track of. Oye!
Are you familiar with G2, or dpont's shadow node? I have run across mention of both of those today on other forums. Just wonder what you thought of them.
Well, I'd better buck up and start reworking my scenes. Thanks again!

07-12-2007, 02:40 PM
To be honest, no, I'm not familiar with them.

Also, rendering dissolves can be very, very, veeeeery slow, so you might end up rendering 100 frames without dissolving quicker than 5 frames of dissolves (or even worse, a 30% transparency).
(My partner once sent a scene to the render farm, 5 minutes per frame... except for a couple of frames that took up to 3 hours to render... which was due to dissolves. 36 times slower than the usual frame for the sequence).
Granted, it needs more planning, but you will be rewarded with a lot more flexibility, and maybe even a shorter total rendering time.