TITLE: Batteries Not Included
NAME: John Aughey
COUNTRY: United States
EMAIL: jha@aughey.com
TOPIC: Toys
COPYRIGHT: I SUBMIT TO THE STANDARD RAYTRACING COMPETITION COPYRIGHT.
MPGFILE: marble.mpg
RENDERER USED: 
    Povray

TOOLS USED: 
    Self written Perl script

CREATION TIME: 
    14 hours

HARDWARE USED: 
    300Mhz Pentium II

ANIMATION DESCRIPTION: 

This animation shows a steel marble rolling down a 2 gague wire track.

DESCRIPTION OF HOW THIS IMAGE WAS CREATED:
The entire animation was created using a Perl script I wrote.  Much of
the viewer code was taken from my submission to the January 1998
animation contest, snake.mpg.

The script reads in an input file consisting of control points for the
track.  These control points are used to build a cubic spline curve
which is used to draw the actual track.  This input file also contains
information for vertical supports, flags, and camera orientation.

Once the spline functions are created for the track, a function
traverses the splines and generates short cylinders which represent
the track.  The angle between 2 adjecent cylinders is at most 1
degree.  A sphere is placed at the joining point of each cylinder pair
to elimate the gap that would be visible between the two cylinders.
All of these short cylinders joined head to tail give the illusion of
one solid wire track.  7642 cylinders and 7642 spheres are used to
create the track.

Second, a function traverses the spline functions again to compute the
ball position at each frame of the animation.  The acceleration due to
gravity is taken into consideration so the ball will speed up and slow
down as it goes down and up hills.  When the ball hits the stop at the
end of the track, the velocity vector is reversed and greatly
dimished.  From there, friction takes over to slow the ball down to a
stop.

The camera motion uses 5 seperate spline curves to determine the x,y,z
focal point and the x,y angle.  The control points for the x,y angle
splines are created from values in the input file.  The control points
for the x,y,z focal point splines are created using the ball sequence
points.  If each ball point were used as a control point for this
spline, then the ball would be in the exact center of the image for
each frame.  Instead, every 15th ball point is used as a control point.
This causes the camera to look in the general direction of the ball,
but not focused right on it.  The camera also lags a few frames behind
the ball.  This combined with the fluid angular changes creates a very
pleasing camera motion.

The Perl script uses the Tk and OpenGL module to provide a user
interface to the animation.  Sliders are available to control every
aspect of the animation.  Camera angle, position, lens, frame lag, and
slack can be changed to view the animation from any angle.  Any
changes are reflected in the OpenGL window which displays the current
scene.  All changes can be viewed in real time to see the effect on
the image.  The animation can be viewed in OpenGL window over and over
again until the desired effect is accomplished.  

When I am ready to create the animation using Povray, I click on the
Povray tab, select the image size and quality, and hit go.  A total
time and estimated time to complete is updated continously so I know
when to return from my coffee break.

VIEWING RECOMMENDATIONS: 

This is a rather large animation, ~590 frames, and the surface the
track is placed on is rather complex.  As a consequence, the mpeg
image quality suffers.  You may notice unavoidable compression
artifacts.  This animation is best viewed between 20 and 25 fps.