CLIM mail archive

# do geometry operations work?

```    Date: Thu, 5 Mar 1992 21:25 EST
From: "William M. York" <York@chuck-jones.west.dialnet.ila.com>

Date: Thu, 5 Mar 1992 16:08 PST
From: Jonathan Amsterdam <jba@ai.mit.edu>

Question 2 is, when these things do eventually work,
are they just going to create region-sets, or are they going to make some
effort to create a drawable thing?  If the intersection of two
polygons is a polygon, I'd like to get my hands on that polygon, not on
some object which says "this is the intersection of two polygons".
Apologies in advance for my naivete--I was hoping to use this piece of CLIM
as the substrate for some genuine 2D geometrical reasoning.

For now the non-rectangle cases are handled by the
REGION-DIFFERENCE object fallback.  This is just due to lack of
any resources focused in this area.  Apparently not much use is
being made of polygon arithmetic, since the problem report above
is somewhat of a show-stopper.

If someone came up with some good polygon-intersection and
-difference code, I'm sure that the right methods for REGION-XXX
on polygon classes could be added to CLIM.  Sorry.

It is currently the intention that CLIM 2.0 will either relegate the
more complex region code to PROVIDEd modules that can be requested via
REQUIRE, or eliminated altogether.  Unfortunately, as Bill points out,
there has been insufficient attention focused on this area.

There are a few questions that CLIM users need to answer on this subject:
(1) How important is it that a full complement of region arithmetic be
provided so that people can do 2D geometrical reasoning?
(2) Is it sufficient to provide just enough functionality so that
people can simply render these objects?  (This is less work then
providing support for doing reasoning.)
(3) What things would you give up in order to support (1) or (2).  That
is, what is less important?  Examples of things to trade off
against include support for gadgets, support for fast low-level
drawing optimizations, support for "color maps", and so forth.

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