Posted by Kristian Olivero (68.12.65.26) on July 23, 2002 at 09:42:10:

In Reply to: Computational Solid Geometry posted by Thanh Son on July 19, 2002 at 00:00:14:

Hi,
You don't mention which API, but you can setup things to draw dashed lines. If I remember correctly, many video cards don't support the custom line drawing, so that may not be the best approach. What you're trying to do isn't too hard to fake though.

-First, draw your geometry normally.
-Second, turn on wireframe mode, and draw the geometry again...this will give you your front outlines.
-Third, reverse your backface culling (so back facing triangles are drawn), and turn on alpha blending (which mode depends on the effect, try a couple and see what looks good). Also, turn off zbuffer. Draw again in wireframe mode to get the back face outlines.

You can change the effect a bit by changing the order of the abover. This won't look exactly like textbooks though, since on objects like cubes you will have an extra diagonal drawn on each face, since these are made of triangles. You would need an extra primitive made of only lines to draw the outline exactly.

If you need more specifics, let me know!

best regards,
Kristian Olivero
president, ba3D Software
www.ba3D.com
DrKO@ba3D.com

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