On Jan 20, 7:23 am, Jon Harrop <j...@[EMAIL PROTECTED]
> wrote:
> I was reading up on real time ray tracing and stumbled upon this demo:
>
> http://www.flipcode.com/cgi-bin/fcarticles.cgi?show=65091
>
> it is one of the best such demos that I've seen.
>
You haven't seen much then I guess :)
> I thought I'd try my hand at remaking the demo using OpenGL instead of
ray
> tracing:
>
> http://www.ffconsultancy.com/free/bunny/
>
> When hardware accelerated, the OpenGL-based renderer can render the same
> image over 100x faster than the real time ray tracer with 1/10th as much
> code.
>
First of all, have you got any idea how much more FP power your GPU has
compared to the CPU?
You seem not to use shadowing in your example whereas ray tracer has
dynamic pixel-perfect self-shadowing. Please add it to your demo and
then come back to compare the two. Vertex lighting is not shadowing.
Another interesting thing would be if you would try to render that
Buddha statue with full detail (~1M triangles) and with (pixel perfect)
shadows. I wouldn't be too surprised when CPU would beat HW accelerated
OpenGL in that scenario even though it has much less raw power.
Anyway, ray tracing a bunny isn't really the best thing to do with ray
tracing. Add in some reflections-refractions and shadows and then start
comparing RT vs rasterizing in terms of speed, FLOPS used and code
length.
> But I noticed something else interesting. When my graphics drivers were
> broken and OpenGL resorted to software rendering, it was still faster
than
> the ray tracer.
>
As I said, your test scene wasn't good when comparing the two rendering
algorithms. Add shadows to your demo and then we'll talk about if
software OpenGL is faster than software ray tracing.
> This leads me to think that a z-buffer (or s-buffer) might be a better
way
> to render primary rays in a ray tracer. Tracing ray bundles seems like a
> first step in this direction.
>
It wouldn't help all that much since primary rays take only part of the
time in rendering. When you add in shadows and secondary rays then
tracing primaries won't make a big difference any more, especially when
you use things such as MLRTA.
> PS: Anyone got any links to better real time ray tracing demos?
Of course:
http://ompf.org/forum/index.php
Look under "visuals" and "tools, demos & sources". Especially
interesting is the Arauna tracer, availiable here:
http://ompf.org/forum/viewtopic.php?p=2721#2721
> --
> Dr Jon D Harrop, Flying Frog Consultancy
> Objective CAML for
Scientistshttp://www.ffconsultancy.com/products/ocaml_for_scientists/index.html...
Ahh, the ffconsultancy. Have you already forgot the thread that was
here around 1.5 years ago?
http://groups.google.com/group/comp.graphics.rendering.raytracing/browse_frm/thread/3119086d94a78fa3/3e82fd2ec7e68189?tvc=1
I'd like to make a request for you. You already have a program on your
home page that renders a sphereflake using occlam. What would be the
speed and code length of comparable OpenGL program?
In case you have forgot where it is, here is a link:
http://www.ffconsultancy.com/free/ray_tracer/index.html
|
