6 ms·

Hi there, code author here. I've been lurking here for years, but couldn't resist an invitation like this. I've always enjoyed Fabien's analyses so it's great

by a_e_k 13y ago

Hi there, code author here. I've been lurking here for years, but couldn't resist an invitation like this. 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.

fabien_sanglard 13y ago
Thanks Andrew, that 'c' variable was giving me a headache ;) ! I have updated the article with your remarks. BTW, I have listed a few good resources about raytracing at the bottom of the page: Do you know any other good books/websites ?
- antirez 13y ago
  Some time ago I wrote a raytracing program in javascript that is supposed to be very simple to understand: https://github.com/antirez/jsrt/blob/master/rt.html https://github.com/antirez/jsrt/blob/master/rt.html Demo here: http://antirez.com/misc/rt.html http://antirez.com/misc/rt.html
  - Uchikoma 13y ago
    Nice! We did a real time raytracer with 2 spheres where you could move around one with C and a cluster of DEC Alphas 20 years ago, funny to see this on my laptop in Javascript (!) now.
- a_e_k 13y ago
  You're welcome! 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/ http://tog.acm.org/resources/RTNews/html/ (Somewhat dead, but the archives are great) * http://ompf2.com/ http://ompf2.com/ (Active, lots of ray tracing specific discussion) * http://www.realtimerendering.com/ http://www.realtimerendering.com/ (I'm fond of the book as well) * http://kesen.realtimerendering.com/ 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.
raminf 13y ago
#define op operator #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.
- fabien_sanglard 13y ago
  Can you pastebin.com it so we can see what it looks like ?
  - raminf 13y ago
    http://pastebin.com/ktukPBHE http://pastebin.com/ktukPBHE 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-newspaper-designs/ http://www.smashingmagazine.com/2008/02/11/award-winning-new...
- zem 13y ago
  #defines have to be one to a line, though - in this case, where you're optimising for layout rather than bytes, i'm not sure it would be a net win. counting, there are 5 instances of "operator", so that's a saving of 36 chars versus 40 taken up by the #define (including the whitespace at the end). there are 10 "return"s, so saving 40 chars there just about draws you even.
- a_e_k 13y ago
  Thanks, glad you liked it! 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.
fabien_sanglard 13y ago
How come you decided for a coordinate system with Z pointing up instead of the traditional right hand/left hands coordinate systems ?
- a_e_k 13y ago
  Actually, Z-up coordinate systems can also be called right or left handed depending on which way Y points. :-) 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.
- mistercow 13y ago
  In non-programming math contexts, it's pretty standard for Z to point up. I have no idea why, as it seems to me like the typical way it works in graphics programming is the more obvious extension of 2D plotting into 3D.
  - Sharlin 13y ago
    As far as I know, in the CAD world Z is typically up/down. It makes sense if you look at the scene from above, like an architect a floor plan - world-space X and Y map to screen-space X and Y, and Z is then the depth. In a 3D virtual world, on the other hand, the perspective is usually of a person embedded in the world, in which case "Y is up" is more intuitive.
    - mistercow 13y ago
      OK, thinking about the architecture angle finally made it click for me.
  - Luc 13y ago
    It makes sense if you think of the X and Y axis as being drawn on paper, which usually lies flat on the desk.
vldr 13y ago
As a (poor :) 3d/raytrace excercise, I've translated the code to python: http://vanderwijk.info/blog/business-card-raytracer-in-python/ http://vanderwijk.info/blog/business-card-raytracer-in-pytho...

by a_e_k 13y ago

fabien_sanglard 13y ago

Thanks Andrew, that 'c' variable was giving me a headache ;) ! I have updated the article with your remarks. BTW, I have listed a few good resources about raytracing at the bottom of the page: Do you know any other good books/websites ?

antirez 13y ago
Some time ago I wrote a raytracing program in javascript that is supposed to be very simple to understand: https://github.com/antirez/jsrt/blob/master/rt.html https://github.com/antirez/jsrt/blob/master/rt.html Demo here: http://antirez.com/misc/rt.html http://antirez.com/misc/rt.html
- Uchikoma 13y ago
  Nice! We did a real time raytracer with 2 spheres where you could move around one with C and a cluster of DEC Alphas 20 years ago, funny to see this on my laptop in Javascript (!) now.
a_e_k 13y ago
You're welcome! 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/ http://tog.acm.org/resources/RTNews/html/ (Somewhat dead, but the archives are great) * http://ompf2.com/ http://ompf2.com/ (Active, lots of ray tracing specific discussion) * http://www.realtimerendering.com/ http://www.realtimerendering.com/ (I'm fond of the book as well) * http://kesen.realtimerendering.com/ 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.

raminf 13y ago

#define op operator #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.

fabien_sanglard 13y ago
Can you pastebin.com it so we can see what it looks like ?
- raminf 13y ago
  http://pastebin.com/ktukPBHE http://pastebin.com/ktukPBHE 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-newspaper-designs/ http://www.smashingmagazine.com/2008/02/11/award-winning-new...
zem 13y ago
#defines have to be one to a line, though - in this case, where you're optimising for layout rather than bytes, i'm not sure it would be a net win. counting, there are 5 instances of "operator", so that's a saving of 36 chars versus 40 taken up by the #define (including the whitespace at the end). there are 10 "return"s, so saving 40 chars there just about draws you even.
a_e_k 13y ago
Thanks, glad you liked it! 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.

fabien_sanglard 13y ago

How come you decided for a coordinate system with Z pointing up instead of the traditional right hand/left hands coordinate systems ?

a_e_k 13y ago
Actually, Z-up coordinate systems can also be called right or left handed depending on which way Y points. :-) 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.
mistercow 13y ago
In non-programming math contexts, it's pretty standard for Z to point up. I have no idea why, as it seems to me like the typical way it works in graphics programming is the more obvious extension of 2D plotting into 3D.
- Sharlin 13y ago
  As far as I know, in the CAD world Z is typically up/down. It makes sense if you look at the scene from above, like an architect a floor plan - world-space X and Y map to screen-space X and Y, and Z is then the depth. In a 3D virtual world, on the other hand, the perspective is usually of a person embedded in the world, in which case "Y is up" is more intuitive.
  - mistercow 13y ago
    OK, thinking about the architecture angle finally made it click for me.
- Luc 13y ago
  It makes sense if you think of the X and Y axis as being drawn on paper, which usually lies flat on the desk.

vldr 13y ago

As a (poor :) 3d/raytrace excercise, I've translated the code to python: http://vanderwijk.info/blog/business-card-raytracer-in-python/ http://vanderwijk.info/blog/business-card-raytracer-in-pytho...