[fa.editor-p] Graphic Editing

C70:editor-people (06/27/82)

>From LAWS@SRI-AI Sun Jun 27 16:30:23 1982
The new issue of ACM Transactions on Graphics (April '82, Vol. 1,
No. 2) begins a regular column of concise descriptions of techniques
for interacting with graphic devices.  The two initial techniques
are on stretching and moving rectangles using a pointing device and
on interactive scaling of arbitrary shapes.

This issue also has an article by C.J. Van Wyk on a TROFF-compatible
language for specifying line drawings.  The IDEAL system is evidently
an outgrowth of METAFONT.  I would describe its chief features as:

  * An underlying algorithmic specification of how to draw figures
    given a set of coordinates or parameters.  The algebraic
    primitives operate in the complex domain to simplify rotation
    and scaling.  (I am not convinced that this domain is easier
    to use than one based on object-centered polar coordinates,
    but it certainly is powerful.)

  * An exceptionally fine mechanism for specifying the parameters
    of an object as a set of algebraic constraints rather than a
    set of parameter assignments.  The user may thus specify those
    relationships which he knows; the computer will then solve for
    the remainder.

  * A clean naming system which allows the user to refer to objects
    or to their internal variables (whether supplied by the user or
    computed from constraints).

  * An iteration mechanism for constructing dotted lines, textured
    region fill, and repeated patterns.

  * An opaquing capability so that later objects may overlay and
    obscure earlier ones.  This may also be used to mask a "textured
    brush" stroke so that it covers only a particular polygon (or
    its surround).

  * An annotation language for positioning labels relative to the
    symbolic coordinates of an object.

This system seems to offer both capability and convenience for
constructing technical line drawings.

					-- Kenneth Laws
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