Now that it's easier to swap out "tracers", it was a snap to, for example, drop one in that visualizes normals instead of doing normal raytracing, the results of which you see below.
Additionally, after the rewrite I didn't even need to worry about where those weird speckles were coming from in my previous refraction blog entry. I think adding a ShadeRecord to the hit functions of all my objects took care of that problem. So I started working on splitting the energy between reflected and refracted rays by just dividing it in half everywhere.
Then I tried fiddling with the constant value a bit. This resulted in interesting images, but they're definitely not correct.
The red sphere which appears on the surface of the left-most sphere in this scene is actually behind it and it's image is visible due to refraction. I don't seem to have to the reflections here.
Now in the image below you can see that the reflection of the red sphere, which should have become more visible in it's transparent neighbor due to the incidental view angle on the transparent sphere, is completely missing. So my Fresnel term isn't working yet.
Oh, is this more like it? I can see below that when my view angle at a transparent sphere hit point gets closer to 90 degrees from the normal, the reflections on the surface of the sphere are more visible, but where my view angle is close to the normal angle, I see more of the refraction.
I don't know. These sphere's look weird, below. They don't seem to have any blending between where you see refracted and reflected images. The whole set of seven spheres have indices of refraction ranging from 1.1 to 1.7, and to me, the lower ior spheres look better. Maybe that's because a perfect sphere with an ior of 1.7 just doesn't exist in nature, so my eye isn't used to what it should look like?
It's very pronounced below. Around the edges, you see all reflection, and in the middle you see all refraction.
I'm definitely missing something, because when I set a sphere's index of refraction to 1.0, it still completely disappears.
In image below, I tried setting the index of refraction of this sphere to something less than that of air. I believe it was 0.9.
Below you can see all seven spheres in one shot, the one with the lowest index of refraction is on the right, the sphere with the highest is on the left.
This one is still a mystery to me. I put my camera inside this sphere, and I get a mess! If this is what is seen from inside the sphere, why doesn't it show up in refracted rays that leave the sphere and reflect off other objects?
I'm not sure it's correct, but I like this image below, looking down the line of spheres, with the dark side of the scene in the background.
Here I decided to take a little break and get some color filtering, or attenuation due to Beer's Law, working while I keep working on the Fresnel term.
I'm currently working on getting OBJ file reading working. I'm actually just wrapping up some code I found from Nate Robins to read the OBJ files, and then I'm going to create a compound object in my geometric object hierarchy which will allow me to contain all the triangles of an OBJ file in a BVH within the compound object itself. Hopefully soon I'll have a Frank model rendered as colored glass!
I'm also still working on getting other types of compound objects working which can be composed of parts of implicitly defined objects.
Ok, well I got a good tip to visualize the fresnel terms on my transparent spheres and see if they, indeed, looked like a step function as all the above images seem to indicate. The following sequence of images illustrate the situation.
Above is an image created by a "Tracer" which keeps only refracted rays from transparent surfaces, and doesn't even compute reflections at all. Now look at the image below, created by my buggy tracer which computes the Fresnel term and allows for wavelength-dependent absorption in the medium of each sphere.
Instead of a gradual change from refraction to reflectance as rays approach hitting the sphere at a glancing angle, there appears to be an arbitrary cutoff. So in the next image, I'm visualizing this Fresnel term which determines the reflect/refract ratio, and it's clearly a step function. The white outer rim indicates a Fresnel term of 1.0, corresponding to pure reflection and no refraction, the black inner circle indicates a Fresnel term of 0.0, corresponding to pure refraction.
So I went to work and found the problem, now that I was sure where it was. When I had fixed the problem, the first thing I saw were much more reasonable looking Fresnel terms, seen below.
So then I went back to doing the normal refraction/reflection rendering, and the images immediately looked a lot better. Notice in the following images that the reflections on the spheres are visible pretty much all over, but they're very faint when you look straight into the center of the sphere, and they get more visible as you look closer to the edge of the sphere.
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