View Full Version : hello

04 April 2009, 06:36 PM
I'd like some help from someone that understands light fogs.

Im trying to create a spotlight with a image-gobo that also is supposed to have a light fog. I've created a spotlight and connected the image (jpeg) to its color node. The light itself falls nicely on the plane in the shape of the white part of the image but the light fog doesn't react the same way at all. it either light up entirely in the shape of the whole conevolyme or doesnt display at all.

I've almost had a nervous break down today because of this so I'd appricate any thoughts regarding this alot.

Best Regards

04 April 2009, 07:27 PM
What software? Is your light fog cone scaled enough to encompass the entire area of intensity? Are you making sure to use depth mapped shadows?

04 April 2009, 07:44 PM
oh right, i'm using maya. I think the coneshape is allright although I haven't tried to scale the it individually,, just the whole cone angle of the spotlight itself. and i've tried to switch on both depth map and raytraced shadows using both maya software or mental ray.

I just descovered that light fog doesnt respond to a gobopicture even though it has an alphachannel. not may way, anyway.

so my ideas are starting to run out!!

04 April 2009, 07:49 PM
Transparency does not work with normal depth mapped shadows, that's where your issue lies. However, if you're using mental ray under the mental ray options for your light you can enable 'detail shadow map' and that should fix your problem after making adjustments.

04 April 2009, 09:30 PM
ok. im not sure im doing this right (im a little new to all this) but I've switched to "detail shadow map" and also enabled the shadow map override (?) and don som tweaking (turning on raytraced shadows, increasing samples and shadowrays etc) but it doesnt happen anything.

Are you sure your method work even though im using a picture to mask the light instead of a polygon??

04 April 2009, 09:36 PM
this is whats going on inside my maya:

04 April 2009, 10:35 PM
When using a detail shadow map you cannot have raytracing on for the light, you need to have depth maps on. Does the light fog work without the image attached? Try starting at the most basic thing, your light with no gobo, and light fog. When that's working, enable your gobo and then when that's working try the shadows. Using this method you'll be able to pinpoint exactly where your issue is.

04 April 2009, 11:09 PM
ok! I thought depthmap shadows didnt work so well in mental ray, but lets try it anyway. I'm all out of ideas anyway.

this is the workflow thats been most successful:

1. create a spotlight, switch on lighFog
2. attach the image (jpeg, grayscaled with white text and black background)
3. that results in a visible fog around the text shaped as the cone and negative area revealing the text. so i figure, if I just invert the texture file in the effects tab I'd get the opposite lightvolyme illuminated, but noo, the text simply appears in white, as you can se in the screenshot I attached. (only in that scene I've also connected a colorramp to the colorgain channel of the texture mask.)

and thats as close as I get

04 April 2009, 12:53 AM
If you still can't get it working my last suggestion would be to, instead of using an alpha for transparency, just use black. It will effectively do the same thing.

04 April 2009, 08:33 AM
that did actually make a change!!!

thank you very much for your help, sir!
very impressive portfolio by the way :)

all the best

04 April 2009, 10:57 AM
Thank you! glad to be able to help!

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04 April 2009, 10:57 AM
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