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45e9809aff7304721fddb95654901b32195c9c7avboxsyncfrom The Open Group.
45e9809aff7304721fddb95654901b32195c9c7avboxsync * Written by Brian Kelleher; Jan 1985
45e9809aff7304721fddb95654901b32195c9c7avboxsync * This file contains a few macros to help track
45e9809aff7304721fddb95654901b32195c9c7avboxsync * the edge of a filled object. The object is assumed
45e9809aff7304721fddb95654901b32195c9c7avboxsync * to be filled in scanline order, and thus the
45e9809aff7304721fddb95654901b32195c9c7avboxsync * algorithm used is an extension of Bresenham's line
45e9809aff7304721fddb95654901b32195c9c7avboxsync * drawing algorithm which assumes that y is always the
45e9809aff7304721fddb95654901b32195c9c7avboxsync * major axis.
45e9809aff7304721fddb95654901b32195c9c7avboxsync * Since these pieces of code are the same for any filled shape,
45e9809aff7304721fddb95654901b32195c9c7avboxsync * it is more convenient to gather the library in one
45e9809aff7304721fddb95654901b32195c9c7avboxsync * place, but since these pieces of code are also in
45e9809aff7304721fddb95654901b32195c9c7avboxsync * the inner loops of output primitives, procedure call
45e9809aff7304721fddb95654901b32195c9c7avboxsync * overhead is out of the question.
45e9809aff7304721fddb95654901b32195c9c7avboxsync * See the author for a derivation if needed.
45e9809aff7304721fddb95654901b32195c9c7avboxsync * In scan converting polygons, we want to choose those pixels
45e9809aff7304721fddb95654901b32195c9c7avboxsync * which are inside the polygon. Thus, we add .5 to the starting
45e9809aff7304721fddb95654901b32195c9c7avboxsync * x coordinate for both left and right edges. Now we choose the
45e9809aff7304721fddb95654901b32195c9c7avboxsync * first pixel which is inside the pgon for the left edge and the
45e9809aff7304721fddb95654901b32195c9c7avboxsync * first pixel which is outside the pgon for the right edge.
45e9809aff7304721fddb95654901b32195c9c7avboxsync * Draw the left pixel, but not the right.
45e9809aff7304721fddb95654901b32195c9c7avboxsync * How to add .5 to the starting x coordinate:
45e9809aff7304721fddb95654901b32195c9c7avboxsync * If the edge is moving to the right, then subtract dy from the
45e9809aff7304721fddb95654901b32195c9c7avboxsync * error term from the general form of the algorithm.
45e9809aff7304721fddb95654901b32195c9c7avboxsync * If the edge is moving to the left, then add dy to the error term.
45e9809aff7304721fddb95654901b32195c9c7avboxsync * The reason for the difference between edges moving to the left
45e9809aff7304721fddb95654901b32195c9c7avboxsync * and edges moving to the right is simple: If an edge is moving
45e9809aff7304721fddb95654901b32195c9c7avboxsync * to the right, then we want the algorithm to flip immediately.
45e9809aff7304721fddb95654901b32195c9c7avboxsync * If it is moving to the left, then we don't want it to flip until
45e9809aff7304721fddb95654901b32195c9c7avboxsync * we traverse an entire pixel.
45e9809aff7304721fddb95654901b32195c9c7avboxsync#define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) { \
45e9809aff7304721fddb95654901b32195c9c7avboxsync * if the edge is horizontal, then it is ignored \
45e9809aff7304721fddb95654901b32195c9c7avboxsync * and assumed not to be processed. Otherwise, do this stuff. \
45e9809aff7304721fddb95654901b32195c9c7avboxsync if ((dy) != 0) { \
45e9809aff7304721fddb95654901b32195c9c7avboxsync if (dx < 0) { \
45e9809aff7304721fddb95654901b32195c9c7avboxsync#define BRESINCRPGON(d, minval, m, m1, incr1, incr2) { \
45e9809aff7304721fddb95654901b32195c9c7avboxsync if (m1 > 0) { \
45e9809aff7304721fddb95654901b32195c9c7avboxsync if (d > 0) { \
45e9809aff7304721fddb95654901b32195c9c7avboxsync if (d >= 0) { \
45e9809aff7304721fddb95654901b32195c9c7avboxsync * This structure contains all of the information needed
45e9809aff7304721fddb95654901b32195c9c7avboxsync * to run the bresenham algorithm.
45e9809aff7304721fddb95654901b32195c9c7avboxsync * The variables may be hardcoded into the declarations
45e9809aff7304721fddb95654901b32195c9c7avboxsync * instead of using this structure to make use of
45e9809aff7304721fddb95654901b32195c9c7avboxsync * register declarations.
45e9809aff7304721fddb95654901b32195c9c7avboxsynctypedef struct {
45e9809aff7304721fddb95654901b32195c9c7avboxsync int d; /* decision variable */
45e9809aff7304721fddb95654901b32195c9c7avboxsync#define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \
45e9809aff7304721fddb95654901b32195c9c7avboxsync BRESINITPGON(dmaj, min1, min2, bres.minor, bres.d, \