it turns out that it's not necessary to use IDL IC=100.  using the simple glass refractive/reflective
shader with approx. 0.01 diffuse, I'm seeing the hdri lite go into the glass-front box and it
appears to be bouncing around.  a lite meter inside the box appears to detect about 50% of
the illumination seen by a lite meter outside the box, which might be expected in reality
(darker inside than outside during the day).  I can't tell if the glass is cutting down on diffuse rays
from the hdri as they enter the box.  will try to post render later.

when I look into a room with a sliding glass door half open, I don't see this much vertical deflection, even tho glass IOR is 1.5 or greater, not 1.2.  it appears that the refractive glass is preventing some lite from getting into the box, and is also preventing it from bouncing back out.  presence of small amt. of diffuse has no effect AFAICT.

Quote -
when I look into a room with a sliding glass door half open, I don't see this much vertical deflection,
even tho glass IOR is 1.5 or greater, not 1.2.  it appears that the refractive glass is preventing some
lite from getting into the box, and is also preventing it from bouncing back out.  presence of small
amt. of diffuse has no effect AFAICT.

I've been meaning to address this with a diagram but I've been kind of busy.

The thing about thin glass is this: it has the same refraction as any glass - it is glass. But it is thin. When light enters the glass, it bends towards the normal. Then it travels a very short distance through the glass and reaches the other side. From there, the reverse refraction happens, bending the light back to the original direction it had when it entered in the first place. The result is a photon passing though thin glass does not change direction at all. It simply hops off its original path a tiny bit, but its ultimate path is parallel to its oriignal path. This is completely different from thick or curved glass.

Poser's Refract node does not understand that it should be using the specified IOR when passing from outside to inside, and then the inverse IOR when passing from inside to outside. This is why it looks wrong. It is doing a double entry refraction, instead of a proper entry/exit refraction.

The usual hack to deal with this when using a single layer mesh is to simply set the IOR to a really small value, like 1.05.

Here's the diagram.

Note that if the two sides of the glass at entry and exit are not exactly parallel, then the heading does change.

A curved glass airplane canopy does change the heading a little bit because it isn't flat. The entry point and exit point are not parallel.

Also, even if a glass pane is flat, there are tiny imperfections or undulations in the surface that make it not perfectly flat, so there is some distortion possible. But it is usually so neglible as not easily noticed through casual observation. For the most part, looking through a modern window produces an undistorted view.

BB, did you ever post the shader you were using in the examples earlier in the thread?

Not yet but I will soon.

I hope this thread has not been forgotten! I have a planned poser project where a wine glass is the focal point of the image and I'd like to do it under IDL. I don't want to have to revert back to Poser Pro.

But I dont' have any new solution for IDL. I posted last week - nothing you do in Poser 8 or Poser Pro 2010 makes this work right.

SM needs to fix the IDL. It must honor transparency.

Second, SM needs to let us specify transmission (letting light through) even if we're using refraction.

Meanwhile, I already posted a wine glass weeks ago, with shader that does the glass and the wine. Did you miss it?

The, now banned, DP Hoadley was using it.

Ah, yes, I have that prop. I can hope that maybe SM will take consideration on the problems you've brought up when it comes to transparency and refraction. I can but hope.