I've always enjoyed Fabien's analyses so it's great fun to see what he makes of my own code. Anyway, a few clarifications from what I remember of this. (I wrote this '09, and I don't have my old notes in front of me right now):
* The `n` value returned by the trace function, `T()`, is the surface normal. It returns this whether it hit the plane or a sphere.
* The `r` vector in `S()` is the reflection vector off whatever was hit.
* The mystery `c` point in the `main()` function is the offset from the eye point (ignoring the lens perturbation `t`) to the corner of the focal plane. Note below that we're nominally tracing rays for pixel (x,y) in the direction of ax+by+c. At the image midpoint, this should be `g`.
* "although I suspect this to be a side effect: This is not how soft-shadows are done." True. There are true soft shadows in this, but this isn't where they're computed. That's the job of the randomization where `l` is computed in `S()`.
Anyway, please feel free to ask any questions about it.
BTW, I have listed a few good resources about raytracing at the bottom of the page: Do you know any other good books/websites ?
Scratchapixel was new to me, so thanks for that link. PBRT (which you already have) is definitely a favorite. You also cited Graphics Gems IV but I enjoy dipping into all of them. Other suggestions:
* http://tog.acm.org/resources/RTNews/html/ (Somewhat dead, but the archives are great)
* http://ompf2.com/ (Active, lots of ray tracing specific discussion)
* http://www.realtimerendering.com/ (I'm fond of the book as well)
* http://kesen.realtimerendering.com/ (Especially the sections for "Symposium on Interactive Ray Tracing" and it's successor, "High Performance Graphics")
If I had to pick one, though, it'd be PBRT since it's a unified work that starts from the ground up.
Demo here: http://antirez.com/misc/rt.html
But really, it was just personal preference. Way back when I was learning 3D graphics, I found it easiest to visualize Z as elevation above the XY plane. I'd also used some software that followed that convention (like trueSpace and later 3D Studio Max).
These days, I mainly work with software that tends to favor a Y-up convention by default.
According to legend, this is why the Math and Physics departments hate each other.
X is almost always to the right, so this gives me Y and Z to work with. To satisfy both the positive values into the screen and right handedness I need either Z forward and Y down or Y forward and Z up. Since most of the time you draw a graph with an axis going up rather than down, that settles it.
It's entirely arbitrary in the end, a single matrix will fix any dispute you have amongst peers.
#define rt return
Then replacing the corresponding inline tokens shaves off another 25 bytes from the source without affecting the output or (arguably) the readability.
Sorry, my inner obfuscator couldn't resist :-)
Beautiful bit of coding, btw.
Yes, it's true that even more could have been shaved off and I did explore some #defines. As I recall, there were also some other changes I could have made to shave off yet more. Ultimately, I decided against them for two main reasons. First, they'd need to occupy lines by themselves which I felt created a bigger gap at the top that ruined the aesthetics somewhat. I wanted something that would look nice and roughly fill the 1.75 aspect ratio of a typical US business card. Secondly, as noted in my reply to matthew-wegner below, I'd noticed the file size that I had achieved.
I dunno, I kinda like the current size.
I reformatted it so it would justify right like the original but for some reason Pastebin likes to reflow things.
It turns out the single-character tokens 'u' and 'w' were not being used so repurposing them for the #defines leads to a saving of 46 characters at the cost of an extra line. There are a few other recurring tokens but you hit a point of diminishing return.
One should not, however, lose sight of what an awesomely clever hack the whole thing is. Reminds me of some of the text-flow layouts in old illuminated manuscripts, or the more modern variations here (like the one with the light-bulb): http://www.smashingmagazine.com/2008/02/11/award-winning-new...