TITLE: Coffee Break
NAME: Alexander Ebel
COUNTRY: Germany
EMAIL: alexander.ebel@online.de
WEBPAGE: http://www.desert-of-the-real.de
TOPIC: Frozen Moment
COPYRIGHT: I SUBMIT TO THE STANDARD RAYTRACING COMPETITION COPYRIGHT.
JPGFILE: aecoffee.jpg
RENDERER USED: 

    mental ray for Maya 1.5 (mental ray version 3.1.4.1)


TOOLS USED: 

    Maya 4.5


RENDER TIME: 

    36h:05m:43s


HARDWARE USED: 

    AMD Athlon XP 1701-D



IMAGE DESCRIPTION: 


So the topic was "Frozen Moment". Hey, that's cool! I like that. It didn't need
long to come to the idea of a falling coffee-cup. Everytime when I make me
coffee and walk around with it, I ask myself how it would looks like, if I
would let it fall to the ground with a light spin, and all the coffee would
pour out of it - in bullet-time (or wouldn't it be called "droplet-time" then?
<g>). I ever wanted to do that in an animation. So here's the first picture of
it. The most interesting picture of it. The moment, when the cup hits the
ground (or you could say a nanosecond after it). The moment frozen in time.





DESCRIPTION OF HOW THIS IMAGE WAS CREATED: 


Ok first of all I made the cup. It's a revolved NURBS-Surface with a modified
NURBS-Torus atached to it. I converted it to polygons to "breake" it. Then I
made the room in which all this takes place. I needed a whole room, because I
used global illumination. The table and chairs in the background are modified
objects of my last picture "Paradise Lost" for the IRTC on the
Loneliness-topic. They're just for the mood. Without them you would miss
something in the background. You wouldn't really have the feeling, this
wood-plankets were the ground. So you subconciously recognize this "something"
in the background to be objects on the ground, so you know, this is the ground.
So far, so good. But here's the tricky part: The coffee. I tried diffrent
things, but nothing seemed to work as I wanted. Actually I'm currently working
on a particle-based fluid-dynamics system in C++. But unfortunately it's still
miles away from beeing "finished". So the best method couldn't came to play. So
I thought about the maya-particles and to mel-script them to behave like water
(I could have used my knowledge about water from my own system) and then use a
blobby-shader. But unfortunately mental ray for maya (which I wanted to use
because of the cool global illumination and caustics) isn't yet able to render
the maya-particles. Well, Maya 4.5 has it's own really cool new set of
fluid-dynamics-functions BUT you can't make pouring water with it because you'd
need two fluids then (water and air) because of the possibility of emerging
droplets, and maya in the current version only supports one. So you can make
beautiful clouds and interstellar gas-nebulars and viscous lava and
cigarette-smoke and whole oceans and and... but not pouring water. So at the
end I needed to get my own hands dirty and model the shape of the coffee by
myself. I had a little help from a set of free mel-scripts which are intended
to make pouring fluids in maya, but what I could create with it could only be
considered as a raw estimate. It looked more like mud or something like that.
That's because it's not very accurate by calculating the intermolecular forces
of the fluid to make it fast. So I had a lot of work to tweak it and bend it
and deform it... At the end, well, it's close to what I meant it to be - but
only close. The section direct over the ground isn't very realistic. I think
there should be more drops and less coherent shape, but I hadn't the time to
tweak it endless. So, the time is up, here's my result. Oh, something on the
colors: I thought, as a coffee-picture it should have typical coffee-colors, so
I used all shades of brown. And I chose to make black coffee (usually I drink
it with sugar and cream) because it's optically more interesting this way, when
the background shines trough it. And it was able to cast caustics on the floor
then. By the way, if you should use Mental Ray too, and get nasty errormessages
like "no photons stored after emitting 10000 photons" when you're using
caustics, try this: Place you're whole scene into a closed object (like a box
that is the room, or a sphere that is the universe or something) and invert the
normals of it. Make sure you're objects have the setting "cast + receive
caustics" enabled (more is better, because Mental Ray paradoxically seems to
get faster if it has bigger surfaces to calculate (you can also make your
caustic-casting object bigger, without adjusting the rest)) and the object that
has to cast the caustics must have a "reflected color" not equal to pure black
(since the color of the reflected caustic-photons depends on it). If you're
still get the errormessage, try placing the (photon-emitting) light(s) closer
to the caustic-casting object - much closer. If you can't do this because this
light is crucial in the lighting on your scene, then make an extra spotlight
for the caustics which emitts no specular and no diffuse, so it will not
brighten up the scene, just cast caustics (if you place it close enough to your
object). That's what I did to make it work. I puzzled a long time around with
that. Perhaps you've found a better method, then please tell me.

Oh, one last thing to mention: No real cups were harmed by the making of this
image. ;-)