Shadows on Glass

[FBM]

Greetings,

 

I'm rendering a building we're designing and it has light shaders (brise soleil) above various windows. The rendering is working perfectly and shadows look great.

 

However, the brise-soleil is not casting a shadow onto the glass where there should be one. To verify this I rendered the glass as a solid material and the shadow was there.

 

Any tips on rendering shadows onto glass?

 

Thanks,

 

Julien

[distracted]

Physically that is normal: basic glass doesn't receive shadows.

There are double glazings with special film on them that eventually can receive some traces of shadows. But not the shadows you expect me thinks.

Anyhow, if you really want to see shadows on your glass then you have to reduce the refraction amount I think. It depends on your mat settings I don't know.

[jkletzien]

Precisely speaking glass (transparent or mirror) does receive shadows, however they are so faint that they are negligible.

 

Conservation of energy and all that, but the same principle also ensures glass barely gets brighter when the light hits it (unless the source reflects into your eye). Think about a flashlight on a mirror if you're unconvinced - the mirror doesn't get brighter but conveys the light energy back out to the room.

 

It may be bad news for your client as a lot of architects don't want to hear it (even some pretty smart ones) but glass doesn't hold light or shadow, and the computer in this case is correct.

[ikinman]

Actually glass can show shadows, as long as it hasn't been cleaned in a while...

 

When I started out in rendering (Jebus, it's been almost 20 years now) I had one of my bosses constantly pound that point into me - no shadows on glass, unless it's filthy. It was his personal bugaboo. He would make me and others walk around and look at buildings specifically for shadows on glass, which you obviously wont find.

 

If an architect or client is giving you grief about shadows on glass, politely ask him or her to point out a real-world example of that. That advice works for a lot of things. Everyone who is starting out in rendering should wander around and really look at how materials and buildings behave in light.

[Vince Paske]

I think what often happens is, looking from a distance, there may be surface just behind the glass (blinds etc) that is casting a shadow that gives an illusion of glass casting the shadow. Close up, its easy to see, but from a distance it may fool the brain into thinking the shadow is actually on the glass when it isn't.