The perfect glass

[Mokiloke]

Yes I know this topic comes up again and again, but having read most of the previous posts and following the instructions given by Dave Buchorfer I find that one fundamental item has been neglected.

 

The problem is that when glass is reflecting something dark it should be more transparent, but what I find is that Max raytrace, reflect/refract and Vray all reflect dark objects as black instead of an absence of reflection.

 

The effect is shown perfectly in the rendering by Dibbers in the Finished works forum.

 

How can this be achieved, the only way that I can see that may work is to put a bitmap in the reflection channel and the same bitmap inverted in the opacity channel, does anyone know a better way??

[Wolf]

have a look into your extended parameters rollout of your material,

there is a section called reflection dimming.

this might be what you are after

[Mokiloke]

I read the manual and this parameter only affects objects that are not in direct light, but does not make the glass more tranparent where dark objects are reflects as far as I can tell anyhow.

[Wolf]

how about this

 

add a falloff map to the reflection/refraction map

and set the falloff to be based on shadow light.

now add 2 different raytrace settings in each of the 2 slots.

 

with a bit of tweaking, i think you might get what you are after.

[jucaro]

what you are trying to achieve is the fresnel effect commonly seen on reflective materials. this can be simulated by putting a fall off material in your raytrace material fall off and assigning a fresnel effect.

 

check this site:

http://www.opengl.org/developers/code/sig99/shading99/course_slides/ShadingComputations/sld001.htm

 

[ November 12, 2002, 08:02 AM: Message edited by: jucaro ]

[Christopher Nichols]

... this is in Vray... Mostly Vray Free... but the same principle applies to other rendering engines, including the native 3D Studio Raytracer.

 

Note that this does not include Refraction...

 

Check this out:

 

http://pixelmonkey.freeservers.com/Vray/Glass-01.jpg

[Wolf]

guys..read his post again

he isnt talking about fresnel,

but instead the more transparent areas you see in the real world on glass, when there is a shadow casting on it.

[Mokiloke]

Hey Guys

 

Thanks for the input. I was actually refering to the way that when glass reflects a landscape the part reflecting the sky (bright)is almost completely opaque, where as where the glass is reflecting a building(dark)it is much more transparent). No shadows or glancing angle Fresnel reflections involved.

 

I have found that if I boost the blackness of my environment map with the output colour map to make it output at less than 0 the colour that appears in the reflection is black and not 100% transparency as it should be. (I'm not sure if this is a valid test but surely an object should never reflect black)

[alejandro]

"Thanks for the input. I was actually refering to the way that when glass reflects a landscape the part reflecting the sky (bright)is almost completely opaque, where as where the glass is reflecting a building(dark)it is much more transparent). No shadows or glancing angle Fresnel reflections involved."

 

This may sound a bit simplistic but it actually seems to me that you are talking about specularity and glossyness here.

It seems to me that with those two parameters you can make the glass which reflects more light more opaque as well.

If you wish to add more drama, maybe you can use your opacity and your reflectivity as well by attaching to them a fallof shadow/light (not sure about this one). If anything you could try the falloff mirror but this may require some tricky uvw mapping