First post: reflections and shadows?

[elektrosport]

Despite iot being a great renderer I confused about one issue (and it may just being me who hasn't understood something basic?), here goes:

How come when I create a glass material with the vray material and add reflection it starts casting shadows?

A material with only refraction set to 100% cast no shadow, adding either a fall-off map or checking fresnel with reflect. to 100% make the material cast a "vague" shadow, while unchecking fresnel and leaving reflect at 100% cast a deep shadow.

Where I come from reflections never cast any shadow how come vray works like that?

BTW "affect shadows" is checked.


cheers,
K

[natty]

hi
have you got the Transparent shadows ticked in the light settings... well that depends if you are using standard lights.

[elektrosport]

Shadow is cast with both transparent shadows checked and unchecked.

The light is a standard max directional light with vray shadows.


cheers,
K.

[natty]

im not quite sure what you are trying to achieve ... everything has some sort of density.

[elektrosport]

of course I understand that, but...

I just don't see the logic in the equation: added reflections=added density.

Until recently I thought that it was some sort of refraction bug that didn't allow for 100% transparent glass with the vray material (ie transparent as in not casting shadows) but much to my surprise it seems to be the reflections instead.

Density, I think, should rather be taken care of by refraction or fog, not reflections.

Another odd thing (stumbled upon by my quest for a non-shadow casting reflecting vray mat) is that when adding a vray map to the reflection slot, reflections vary in colour from that of just plain 100% reflections..

It's all very intriguing..


cheers,
K.

[percydaman]

well I think it more a question of caustics. since all light that passes through glass is considered caustics, its rather inefficient to force caustics to get light through glass in a scene.

why is it hard to imagine that the higher reflectivity of a surface the more light is bounced off of it and not through it?

I think you might need to post some images illustrating your point, as i did some tests and didn't get the same results. my glass pane with fresnel reflection didn't cast any more shadows then the pane with no reflections. And if you uncheck fresnel, its going to create 100% reflectivity, why are you surprised that you get shadows? its essentially become a mirror and overriding any refractions. seems to make perfect sense to me.

[egz]

Shadows are created when light does not pass through an object. Reflections reflect parts or all of the light so that it does not pass through. Hence the shadows.

As for a map in the Reflection slot, this is not like adding an environment that you want to be reflected in your object. What you are mapping is the reflective color of the object. That's why you are seeing unexpected colors. If you want to add an environment map (like a reflection map in old style materials) you add this to the environment slot.

[elektrosport]

ok, I'm clearly not tuned or fit to keep the arguments flowing, I know nout about these formulas and how light really works.. I've got a basic understanding and some sense of logic (or a view on how things should be)..

When I open my balcony door and look at the sun shining through the glass and the open door, the difference in shade is not as great as featured in Vray, this even though a piece of light and heat reflective film is added to the pane.
This is where my arguments come to a halt. I'll accept your explanations but only because it really doesn't matter.. The glass will continue to cast shadows, whether I submit to your arguments or not.


As for the vray map in the reflect slot, it was a desperate attempt to see if shadows could be removed..
There are no valid arguments as to why I should do it, other than having worked in 3ds for a decade now have taught me not to dismiss any desperate attempt to fake a wanted result. I was just puzzled by the difference in colour.

To get the glass I want obviously takes me to the standard max material and a material wrapper.. plus those ridiculous (in comparison) rendertimes, can't beat those..


cheers,
K.

[trixian]

Ah...but then in real life, the light that comes through your glass is in "correct" cg terms refracted caustics.....and you don't want to try doing that on a large inerior scene

Fake anything as long as it doesn't look fake I say.

I wonder if we will se any renderer in the future where the artificial difference between diffuse and speculars are removed. Where light is just treated as light. Maybe when im 80 or so.