DMM Varkon® Tutorial
A Beginner's Guide to the Varkon Parametric Modeling and CAD Application Development System
By David M. MacMillan
This is just a quick note pending the completion of a proper description and example.
In Varkon, hidden line removal is accomplished by "dressing" a model in b_planes (bounded planes). A b_plane is a triangular or trapezoidal plane segment which is transparent when viewed from one side and opaque when viewed from the other side. One makes an item appear solid by covering it with b_planes whose opaque side is on the outside. Varkon automatically calculates the intersections of b_planes.
Thus, to make a cube appear solid, you put 6 b_planes on the 6 faces of the cube. To make a cylinder appear solid, you make the cylinder faceted and put b_planes on each of the outside facets. To make the ends solid, you put triangular b_planes on the end in a radial pattern.
To make a plane with a hole in it, you cover the entire plane, except the hole, with trapezoidal b_planes.
An apparent problem arises when doing this, however, because the edges of b_planes are not themselves invisible. Thus, if you use triangular b_planes to define the ends of a cylinder, you get a radial pattern of lines created by the b_planes' edges when hidden line removal is performed. A similar problem occurs when "drilling" a hole in a surface.
The solution to this problem is to define all of the b_planes to be in a different level than the rest of the drawing. That level is then made hidden. b_planes in hidden levels still perform their hidden-line-removal functions, but they themselves are invisible (their edges are invisible). I have found it convenient to reserve one level for the use of hidden b_planes and simply to create all b_planes in that level throughout the entire model.
I hope soon to add an example of a "solid" block with a hole drilled through it.
With the exception of any material noted as being in the public domain, the text, images, and encoding of this document are copyright © 1998 by David M. MacMillan.
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