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Date:         Wed, 02 Jun 93 14:18:43 EDT
From: "Breno A. Silva" <rutgers!brufse.bitnet!INF02>
To: bobsbox.rent.com!lightwave
Subject: Re: Caligari vs Real 3D vs others



MR STUART FERGURSON REPLIED:

>+--  BRENO A. SILVA ([e-mail]) SAID:

>| LET'S MAKE SOME POINTS CLEAR HERE:

>I FEEL THE NEED TO CLARIFY THE CLARIFICATIONS.
And I feel the need to clarify the clarifications to the... well, you
got it!

>| -LIGHTWAVE IS NOT A SOLID MODEL RENDERER, IT'S A POLYGONAL RENDERER.
>| REAL 3D IS A SOLID MODEL RENDERER, WHAT MEANS THAT IT DESCRIBES 3D
>| SURFACES THROUGH MATHEMATICAL EQUATIONS, FASTER TO RENDER AND MUCH MOe
>| MEMORY EFFICIENT. LIGHTWAVE IS A 3D PROGRAM THAT DESCRIBES SURFACES
>| BY MULTIPLE POLYGONS.

>CSG MODELS ARE ONLY MORE EFFICIENT IF YOUR OBJECT CAN BE DESCRIBED
>EFFICIENTLY WITH THE PRIMITIVE SOLIDS ALLOWED BY THE MODELER.  UNLESS
>THERE IS A FRACTAL LANDSCAPE PRIMITIVE IN THE SOLID MODELER, REAL 3D
>WILL PROBABLY BE MUCH MORE INEFFICIENT THAN LIGHTWAVE IN ITS
>DESCRIPTION, FOR EXAMPLE.
'Probably' it's not 'surely', surely. The point you probably forgot
is that CSG models can be described not only by primitives, which
for itself it's enough for lots of applications, and I repeat, face
jaggies-free. You can also modify the CSG model heavily with boolean
operations, and you all know how much boolean operators can be a pain
for polygonal renderers. In Real 3D the calculation is almost instan-
taneous, and the rendering much faster than a mesh-only modeler, with
the extra benefit of not having to worry with points or polygon
proximity, like in Imagine. *But*, if you tryed to say you won't have
much flexibility with CSG, I totally agree with you. A face, for exam-
ple, it's not suited for CSG modelling. The problem is: I didn't say
it! I just said that a similar model in polygons renders slower than
in CSG, but that presumes similar models, i.e., suited for both. Clear?

>| -YOU CAN'T TURN RAYTRACE ON FOR JUST ONE SURFACE.

>NOT SPECIFICALLY, BUT IN EFFECT YOU CAN.  YOU CAN, FOR EXAMPLE, SET UP
>TWO REFLECTIVE SURFACES IN A SCENE, ONE WITH A REFLECTION MAP AND ONE
>WITHOUT, AND IF REFLECTION TRACING IS TURNED ON, THE MAPPED SURFACE
>WILL HAVE REFLECTIONS COMPUTED FROM THE REFLECTION MAP (FAST) AND THE
>OTHER REFLECTIVE SURFACE WILL HAVE REFLECTIONS CALCULATED BY RAYTRACING
>(SLOW).  NOTE THAT THESE TWO OBJECTS CAN BE IN THE SAME SCENE, AND ONLY
>THOSE PIXELS WHICH REQUIRE RAYTRACING WILL INVOKE THE RAYTRACER.  THE
>REFLECTION MAPPED OBJECT CAN EVEN BE REFLECTED IN THE RAYTRACED ONE.
I said it, and I repeat it: You *can't* turn tracing for just 1 surface!
How the renderer proceeds on tracing has nothing to do with what I said!

>| IF YOU ACTIVATE TRACE
>| REFLECTIONS, REFRACTIONS OR SHADOW, YOU ACTIVATE FOR THE WHOLE SCENE.
>| EVEN IF YOUR OBJECT IS ABSOLUTELY NOT TRANSPARENT (NO REFRACTION NEEDd)
>| NOT REFLECTION MAPPED (NO REFLECTION NEEDED) OR DOESN'T RECEIVE SHADOs
>| (NO SHADOWS NEEDED), YOU WILL STILL SEE A VERY NOTICEABLE RENDERING
>| SLOW-DOWN, MAINLY IN SHADOWS TRACING.
>TO MY KNOWLEDGE, THIS IS FALSE.  SINCE LIGHTWAVE IS A SELECTIVE RAYTRACr,
>IF NO TRACING IS REQUIRED THEN THE RENDERING TIME WILL BE THE SAME WHETer
>RAYTRACING OPTIONS ARE ON OR OFF.  OBVIOUSLY YOU CAN'T HAVE A SLOW-DOWNin
>SHADOW TRACING IF NO SHADOWS ARE TRACED.
Your technical manual-reader knowledge is not totally right. In *practice*,
that's what really means, Even on faster processors, the program slow downs.
Tipically 3-6 seconds. I don't know why it happens, but it's probably - and
that's a guess - in the rendering initializing process, when it first needs
to detect which polygons will be ray-traced or not. As to the slow-down,
it's obviously ridiculous in these situations, but what normally happens is
that you want a water with a high refraction index and a big glass which
should have no ray-tracing, with a refraction index of one. Guess what?
You can't! It will slow, and now will tipically double your rendering time.
Your selective ray-tracer theory now totally fails, as even though the re-
sult will be absolutely the same - this I tested - the rendering time will
be much higher, the software doesn't make any distinction. Sorry for don't
making that out clear enough.

>OH WAIT -- I THINK I SEE WHAT YOU'RE SAYING.  IF YOU HAVE A SHADOW-CASTng
>LIGHT ILLUMINATING A SHADOW-RECEIVING OBJECT, THEN THERE WILL NATURALLY
>BE A SLOW-DOWN SINCE THE PROGRAM HAS TO CALCULATE WHETHER THERE ARE ANY
>SHADOWS ON THE OBJECT.  IF YOU KNOW THERE ARE NONE, JUST TURN OFF
>SHADOWS ON THE LIGHT OR THE OBJECT.  OTHER OBJECTS OR LIGHTS IN THE SCEe
>CAN STILL HAVE SHADOWS.
Same as above.

>| -AS I'VE ALREADY SAID, LIGHTWAVE *CAN* TRACE SHADOWS, BUT VERY UN-
>| REALISTIC DARK AND HARD-EDGED ONES, IN VERSION 2.0.

>THE DARKNESS OF THE SHADOW WILL DEPEND ON WHAT LIGHT FALLS IN THE
>SHADOWED AREA.  IF YOU USE ONLY ONE LIGHT, THEN THE SHADOWED AREA
>WILL BE LIT ONLY BY AMBIENT LIGHT, WHICH CAN LOOK BAD.  USING FILL
>LIGHTS, BACKGROUND LIGHTS AND "RADIOSITY" LIGHTS IN ADDITION TO THE
>KEY LIGHT WILL MAKE A SCENE WITH SHADOWS MUCH MORE REALISTIC.  THIS
>IS A MATTER FOR THE ARTIST, NOT THE SOFTWARE.
I agree, I just gave a typical result, and lot of the top artists have
problems with it in their masterpieces. As to me, I have no problem
with it, as I've developed a soft edge shadow technique since Toaster
2.0 release. There's your artist.

>| IN LIGHTWAVE PRO
>| (TOASTER 4000'S VERSION) YOU CAN HAVE PERFECT SOFT EDGED SHADOWS.
Once again, my "perfect" it's just an overall impression about the
results. If you want to take everything I say literally, mr. Stuart,
I'll probably write you a bible. Anyway, there aren't perfect shadows
(literally) anywhere out of the real world. Full stop.

>NOTE THAT THE SOFT-EDGED SHADOWS IN LIGHTWAVE 3.0 ARE "SHADOW MAP"
>SHADOWS, WHICH ARE NOT RAYTRACED.  THEY CAN BE MANY TIMES FASTER THAN
>RAYTRACED SHADOWS AND WILL BE SEVERAL MORE FACTORS FASTER STILL THAN
>SOFT-EDGED SHADOWS PRODUCED WITH RAYTRACING.
>UNFORTUNATELY, SHADOW MAPPING DOES NOT PRODUCE "PERFECT" SHADOWS IN
>THE GEOMETRIC OPTICS SENSE, BUT THEY CAN LOOK QUITE GOOD IN MANY
>CIRCUMSTANCES.

>| A QUICK TIP HERE: REMEMBER THAT FOR PERFECT SHADOWS, YOU NEED LIGHTS
>| THAT DIMINISH ITS INTENSITY ALONG THE DISTANCE (FALLOFF).
>WHILE THIS MAY BE MORE REALISTIC PHYSICALLY, IT MAY NOT NECESSARILY
>_LOOK_ MORE REALISTIC.  USE JUDGEMENT.
Of course you shall use your judgement! This one is for closed places,
like rooms or bathrooms. Didn't say anything about simulating a landsca-
pe with that!!!! Come on, mr. Stuart, we're talking to people with a mi-
nimal knowledge and good sense! Don't treat them as small children!

>| CALIGARI'S SHADOW'S
>| ARE A BIT BETTER THEN LIGHTWAVE'S AND MUCH FASTER (NOT RAYTRACED).
Once again, just a general impression, NOT a rule.
>LIGHTWAVE'S SHADOW MAP SHADOWS ARE NOT RAYTRACED EITHER.  AS WITH THE
>DIFFERENT REFLECTION METHODS, RAYTRACED SHADOWS AND SHADOW MAP SHADOWS
>CAN BE MIXED IN THE SAME SCENE.
So what? Simply because two renderers use similar methods it doesn't mean
their render quality will be the same or even similar. Not even worth a
comment...


Well, now that I'm aware that there are gramatical and literal-expressions
watchmen,I'll be much more careful about how I say what I say. It's always
boring, though, to see someone take the time to review every comma of what
we said. Anyway, I'm sure that I didn't make any mistake, just didn't made
myself clear enough for a clarification. Next time I'll probably let it to
mr. Literal Fergurson, as I'm tired to pointlessly discuss about minor de-
tails like those. ;)

Cheers,
Breno A. Silva ([e-mail])