DIRECTORY Rope; G3dEdgeBlt: CEDAR DEFINITIONS ~ BEGIN ROPE: TYPE ~ Rope.ROPE; EdgeDesc: TYPE ~ RECORD [ val: INT32, -- current value for incrementation, byte address or value stepsLeft: WORD _ 0, -- number of increments remaining length: WORD _ 0, -- total number of increments to make hiccups: WORD _ 0, -- number of offsets (hiccups) to make lngthIncr: INT16 _ 0, -- amount to increment by hicIncr: INT16 _ 0, -- amount to offset at hiccup bias: INT16 _ 0, -- change to # of increments to first offset (for wizards) indirect: BOOL _ TRUE, -- incrementing addresses if TRUE, else values nextEdge: CARD16 _ 0 -- next edge if part of a chain of edges (index in sequence) ]; EdgeSequence: TYPE ~ RECORD [ length: CARDINAL _ 0, element: SEQUENCE maxLength: CARDINAL OF EdgeDesc]; EdgeBltOptions: TYPE ~ RECORD [ includeStart: BOOL _ TRUE, -- include start point includeEnd: BOOL _ TRUE -- include endpoint ]; defaultOptions: EdgeBltOptions ~ [TRUE, TRUE]; EdgeBltTable: TYPE ~ RECORD [ dst, src: EdgeDesc, options: EdgeBltOptions _ defaultOptions ]; Error: SIGNAL [code: ATOM, reason: ROPE]; Incr: PROC [edge: EdgeDesc, array: REF EdgeSequence _ NIL] RETURNS [EdgeDesc]; Blt: PROC [ebt: EdgeBltTable]; END. ψG3dEdgeBlt.mesa Copyright Σ 1987 by Xerox Corporation. All rights reserved. Frank Crow, April 20, 1989 2:05:11 pm PDT A general-purpose Bresenham incrementer. Type Definitions Basic Procedures The fractional increment Dy/Dx must be added to y for every new position x. Whenever the fraction overflows, y is incremented, effectively subtracting 1 from the fraction. By removing the fractional part from y, we can instead increment by Dy until Dx is reached. To center the positions of the y-increments along x, the incrementation by Dy should be started at Dx/2. To further simplify, decrement by 2Dy and start at Dx, testing for < 0. In the following read Dx as longSize and Dy as shortSize. Increments EdgeDesc once unless runToHiccup is set. Κ^˜™J™