Re: Refracted ray

Hn <Hn@[EMAIL PROTECTED]
> writes:
>>    glass air
>>    glass water
>>    glass ice
>>
>> depending on where a ray is.  Today I use a list of medium being
>> traversed but I can't seem to be able to exit a material directly
>> into another one..
>
> Can you use a stack? Push the old IOR's as you enter a new medium (from
> the 'front' ), then pop them back when you exit a medium (from the back)

I suspect he's already using a stack (the "list of medium being
traversed"), but the problem is often it's convenient to be able to have
"objects" which aren't properly nested.

E.g.,
                              R
                             /
      ---+       +----------4-+        +---
         |       |    I    /  |        |
         +-------+--------3---+--------+
          \      |       /    |       /
          |      +------2-----+       |
          |            /              |
          |          W/               |
           \         /               /
           +--------1----------------+
                   /
              G   .
                 .
         -------0-----------------------

I being the ice cube, W the water and G the glass.  The ray R traverses
various interfaces at points 1 - 4.

You can handle the G->W at point 1 transition using the method I
previously mentioned (since that interface is probably static), and the
W->I interface at point 2 because it's an "entering" transition, but
what do you do at point 3 and 4?

That would seem more amenable to treating the list of "active" media as
a set than as a proper stack -- e.g., when you make an "exit"
transition, go back through the history of the ray, and find the
innermost medium which hasn't been exited.

So at point 3, you have a ray history like:

   0: enter G, from IOR = 1
   1: exit  G
    + enter W   (special handling because it's a dual interface)
   2: enter I, from IOR = W's IOR
   3: exit  W

[The "from IOR" at each "enter" point is just whatever IOR was current
at that point.]

I is the innermost active medium, so you'd use W's IOR as the new
current IOR.

At point 4, you have additionally:

   4: exit I

So no medium is active, and you'd just use 1 as the new IOR.

[I suppose the overlap between the ice cube and the water isn't quite
proper, but it's very convenient from a scene-definition point of view
to be able to do that kind of thing...]

-Miles
--
My spirit felt washed.  With blood.  [Eli ****n, on "The Passion of the
Christ"]