kalle.last@[EMAIL PROTECTED]
wrote:
>> 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?
Exactly.
> 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.
I'm working on it. There are plenty of OpenGL programs already out there
with shadowing, of course. Look at Quake 4, for example.
> Vertex lighting is not shadowing.
Indeed.
> 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.
I seriously doubt it. Jacco couldn't ray trace 1M pixels in real time, let
alone triangles...
> Anyway, ray tracing a bunny isn't really the best thing to do with ray
> tracing.
Exactly. Ray tracing only seems to be good for sphereflakes.
> Add in some reflections-refractions and shadows and then start
> comparing RT vs rasterizing in terms of speed, FLOPS used and code
> length.
Shadows won't make any difference. Reflections of distant objects can be
done with cube maps, so that won't make any difference either.
Accurate close-up reflections and refractions you'd need to use something
akin to ray tracing. Use mathematically simple primitives like spheres and
ray tracing has a benefit. So ray tracing is great for reflective
sphereflakes and bad for everything else...
>> 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.
I already added a completely naive shadow rendering algorithm and using
OpenGL is still many times faster than Jacco's ray tracer. I'll optimise
my
OpenGL and post it.
>> 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.
Even in real time ray tracers?
>> 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
The screenshot on that page is about as compelling as Jacco's grainy
bunny.
> 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
Sure, TBP said that sphereflake's should ray trace "in the blink of an
eye".
Then he posted an optimised sphereflake ray tracer to back up his claim.
It took me a year to reply, but TBP's C++ ray tracer turned out to be only
60% faster than the OCaml:
http://groups.google.co.uk/group/comp.graphics.rendering.raytracing/browse_frm/thread/eeefae7a63d2e86d/433095e794bf9ced?lnk=st&q=harrop+ray+tracer&rnum=2&hl=en#433095e794bf9ced
> 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?
OpenGL would not fare well. However, do you have a ray tracer that can
render that in real time? Many people have claimed that is has been done,
but I've never seen anything like it.
--
Dr Jon D Harrop, Flying Frog Consultancy
Objective CAML for Scientists
http://www.ffconsultancy.com/products/ocaml_for_scientists/index.html?usenet
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