raytracing on a white plain...

# 1 25-03-2005 , 03:29 PM

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hey all,

i have a scene which is basically a glass object (ramp shader + reflections mapped to the reflected color) on top of a plane which has a white lambert assigned to it. i have everything set up with raytracing so that the shadow of the glass object is being refracted in the glass object itself. no problems here. but... now i want the plane to be plain white. real white. i usually do this by assigning a back ground shader to the plane and by setting up a plain white image plane. with dmap shading this works fine, but with raytracing it does not. for me at least. in my case i get indeed a plain white plane, but it goes wrong in the refraction part. the plane is refracted BLACK in the glass. so, my glass object is now almost totally black. i tried several things, like playing around with the visible in refraction/reflections for both plane and image plane, but i can't get it to work. when i turn off visible in refractions for the plane, the blackness is gone, but, off course, i have no refraction of the shadow, just the shadow unrefracted. i also played around with the environment colors for camera and object, but black for both seems to be the way to go. when i set them to white i get an almost all white glass object...
i bet there is probably an easier way to set up a totally white plane, but i have not found it so far. can someone point me in the right direction? thanks alot.

tiz

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# 2 25-03-2005 , 05:32 PM

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pics

hey,

thought i provide 2 images that clarify the prob. this is not my actual object, this is just for clarification. the first is how i want it, but then with a whiter plane. the second is a picture of the problem. one can see the point of the plane in the lower right corner. it's black there, because the image plane is not positioned that low. the left top corner of the image plane is refracted BLACK in the sphere. it should just be refracted white. this way the shadow is not visible. it seems as if in refraction the use background shader does not see image planes... therefore it uses the default background color (black). if i change the background color of the environment to white (and delete the image plane), nothing changes, and the plane is refracted black as well. by the way, if i turn reflections on, the white background will turn the whole scene into whiteness, so it's not an option either way. help.

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# 3 25-03-2005 , 05:35 PM

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the prob

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# 4 28-03-2005 , 09:00 PM

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anyone?

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# 5 29-03-2005 , 08:10 AM

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make the colour white and then push the ambient value up to pure white aswell. That will give you a pure white plane.

user added image

Alan

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# 6 29-03-2005 , 07:33 PM

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yes, but... there will be no shadow that way...

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# 7 29-03-2005 , 09:55 PM

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so do a separate shadow pass then... user added image

that's the simplest way to do it rather than attempting to do it all in one render.

Alan

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# 8 30-03-2005 , 07:11 AM

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hey alan, thanks for helping me out here. appreciate it.
seperate passes is not the way to go either i guess. i need the shadow of my object refracted in my object. if i push the ambient value of my plane shader up and render in different passes, i will indeed get:
1. a white plane
2. an object with a white refracted plane
3. a seperate shadow.

only, the shadow is the shadow without refractions. and the object just refracts the white plane, not the shadow anymore. one could leave the ambient value as it is and then do the render pass thing. one is stuck with the color of the plane (not pure white) as it is refracted in the object. post compositing in photoshop (placing a white plane behind the object) will not effect the refracted plane INSIDE the object, which therefore will keep it's own (not pure) white color.

it seems like a very simple problem, but turns out to be not so much... user added image

especially id you have played around with this prob for a while now...

i found a workaround though. it involves using a shading map shader, a lambert and a ramp texture. you can basically let the shading map take all light parts (without shadow) of the plane and make them whiter, while not altering the shadow brightness. maya does this in post. the ramp texture needs some tweeking, but it somehow works. if someone wants to know exactly how it works, let me know and i'll post it here. it is not an ideal method though, so any other suggestions are still welcome! user added image