Transparency maps and light fog ?

# 1 06-03-2008 , 10:20 AM

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Hello 2 all

I have been experimenting with lightfog and transparency maps.

I had an idea on how to generate the light beams for my underwater scene, but I am having trouble getting this setup to work properly.

Ok I have a plane with a blinn applied to it I have mapped a file to the transparency of the blinn, just added a simple checker texture, for this test.

I added a spot light, and added light fog to that and placed it above my plane shining down. when I render It does,t cut out the black squares in the checker texure and allow the light fog to come through. Also I get that harsh light cone on the black(transparent areas) of my plane. Also on the white areas of the plane.
Ok this is just a test, but how can I get the result I am after ??

Any help on this would be great.

Thanks

Andy Gee

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# 2 06-03-2008 , 10:26 AM

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# 3 06-03-2008 , 10:45 AM

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# 4 16-03-2008 , 02:43 AM

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i believe that light fog doesn't go through transparent materials, only through actual holes... so if you wanted the light fog to pass through the floor you'd have to create a panel that actually had holes in it.

as for the harsh white, what is the value of your spotlight? it looks like you've got that sucker cranked up pretty high...

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# 5 17-03-2008 , 04:54 PM

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Hey, as far as getting light fog to pass through transparency objects there is a nice bit of a tutorial at the gnomon workshop found here .

Basically what you need to do is create an object that has the hole you want the fog to go through. Leave the default material on it and open up the objects render settings. Turn the visibility off so that it does not render but it will still affect the light. This will allow you to make it look like the fog is going through the items.

Hope that helps!

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# 6 17-03-2008 , 05:02 PM

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# 7 17-03-2008 , 05:10 PM

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I have attached a quick mockup of what I do believe you were trying to do. Instead of using a texture for transparency I simply plced my plane and cut out the necessary holes to demonstrate the effect. Where the fog seems to separate is where the plan is but as it is not visible in renders it will still affect the light so if you had a textured plane there which did not affect shadows but showed in renders you should be able to achieve your desired look.
I have the file here still if you'd like to see what has been done. All you would have to do is place a plane with your trasnparent texture over the original plane and then adjust its render settings so that it does not affect shaows, and such.

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Last edited by alexanderH; 17-03-2008 at 06:03 PM.

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# 8 17-03-2008 , 11:00 PM

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yea! cut holes in it!

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# 9 17-03-2008 , 11:18 PM

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Hey AlexanderH

How did you cut holes in the geometry ??

The reaon I am asking is because I want to add an image sequence to plane which is animated so I am not sure how to cut holes from an image sequence ?

any further help would be great.

thanks

Andy Gee

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# 10 18-03-2008 , 01:06 AM

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i think for an image sequence you can attach that to the light itself like alexander H shows in the one render... as long as you have an alpha channel attached to the image sequence it should only create the fog within the image's area.

(because to cut holes you have to delete portions of geometry - like faces for polygons or perform trims for nurbs planes...)

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# 11 18-03-2008 , 02:59 PM

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yeah if you are mapping an image to the colour value of the light, if you map that same image sequence to the lightfog it will only have fog where there is colour. Furthermore the color based transparency in the lightfog options will give you more realistic fog based on that image sequence.

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Transparency maps and light fog ?

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