From: utzoo!decvax!ucbvax!C70:editor-people Newsgroups: fa.editor-p Title: Graphic Editing Article-I.D.: ucb.1433 Posted: Sun Jun 27 16:33:24 1982 Received: Tue Jun 29 07:18:21 1982 >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 -------