Path: utzoo!mnetor!uunet!husc6!ut-sally!utah-cs!utah-gr!uplherc!sp7040!obie!wsccs!terry
From: terry@wsccs.UUCP (terry)
Newsgroups: comp.graphics
Subject: Re: Point Graphics
Message-ID: <362@wsccs.UUCP>
Date: 23 Mar 88 03:35:41 GMT
References: <165500005@uiucdcsb>
Lines: 54
Summary: You could...

In article <165500005@uiucdcsb>, mccaugh@uiucdcsb.cs.uiuc.edu writes:
> 
>  I would be very interested in any info on the emerging concept of "point
>  graphics" which is a graphics model assuming 'smart pixels' -- w.g., in 
>  an animation sequence involving the possibility of 2 or more objects
>  colliding, the first (i.e., fastest) object first sets a pixel-set to
>  the value 'occupied' so that other objects moving into the set will
>  cause a collision to be sensed. Presumably, the intent is to avoid
>  computation of first- and second-degree simultaneous equations to
>  decide presence of collision.

	I think that it would be possible to determine a graphics object
via rubber-banding bezier curves.  The method involved would be to simply
define your object in cubic arrangements of points, thereby giving sort
of spline-fractals.  Then you could determine collisions by determining
if any two lines defined by the edge of the cubic had a collision by
using any 3 of the 4 points involved to define a plane and determining
whether or not the fourth point was above or below the plane.  Admittedly,
if your curve exceeded the length of the line segment forming it, either
above or below the segment when projected into the plane defined by the
curve and the points defining the curve, you would have points sticking up
which could not be detected.  I believe this method would work if you
were to do several things:

	1) All points must be an integer unit distance apart, with implied
	   points at one unit intervals, therby describing equally sized
	   cubics which define the objects.

	2) All line segments must exceed or equal in heighth/depth the
	   curves they define, as projected onto them.

	3) The unit distance must be smaller than the resoloution of the
	   collisions to be detected (if your unit length was one millimeter,
	   you collision-detection accuracy could vary -+ a millimeter)

This would have the effect of defining an orthogonal 3 dimensional grid, within
which you could define your points defining your object.  If you have two
objects, this would have the effect of defining cubic objects in a single
reference frame, or multiple reference frames, if the objects are not defined
in cubics which are mutually perpindicular to each other.

Either way, you would simply have to do a matrix transformation for any angle
of approach of any two objects.  You calc the curves only for display
purposes.

	Much simpler!


| Terry Lambert           UUCP: ...{ decvax, ihnp4 }                          |
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| SLC, Utah                                                                   |
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