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From: jbickers@templar.actrix.gen.nz (John Bickers)
Newsgroups: comp.sys.amiga.programmer
Subject: Selecting curves.
Message-ID: <1804.tnews@templar.actrix.gen.nz>
Date: 1 Apr 91 05:41:42 GMT
Organization: TAP, NZAmigaUG.
Lines: 43


    Oops, I accidently deleted the article this is a followup to. The
    question was about selecting a curve, and a proposed solution which
    involved rendering the curve and checking each point for proximity
    with the mouse.

    Another approach, a lot simpler, and the one I'd use (ha, some
    recommendation, huh? :) is to have a pick box associated with the
    curve. It's an approach that I've seen used on a couple of large
    programs - Finale, a Mac scoring program, and Information Engineering
    Workbench, a PClone software engineering tool.

    The idea is to draw a little box at some point along the curve, and
    the user clicks in this to select the thing. You can XOR the box
    in, so it's optional whether it's displayed or not (for example,
    if you have several classes of objects, and only want to allow the
    user to select a particular class, you might only draw the pick
    boxes for objects in that class).

    This seems great for allowing the user to pick up control points for
    curves, endpoints for lines, etc. You can even give the user options
    for how large these pick boxes should be, use different pick boxes
    for different things, etc...

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    One nice thing is that it shows the user exactly where they can
    select, rather than having to have a feel for how close the mouse
    has to be to an object to select it.

    You can use this scheme for selecting anything, including those
    polygon shapes we were talking about before. Using a proper detection
    scheme is better for things like gadgets, where clicking on rectangles
    is what you're trying to avoid in the 1st place, but for clicking
    on objects in a drawing program pick boxes could be nicer.
--
*** John Bickers, TAP, NZAmigaUG.        jbickers@templar.actrix.gen.nz ***
***         "Patterns multiplying, re-direct our view" - Devo.          ***