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cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsyncfrom The Open Group.
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * Written by Brian Kelleher; Jan 1985
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * This file contains a few macros to help track
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * the edge of a filled object. The object is assumed
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * to be filled in scanline order, and thus the
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * algorithm used is an extension of Bresenham's line
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * drawing algorithm which assumes that y is always the
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * major axis.
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * Since these pieces of code are the same for any filled shape,
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * it is more convenient to gather the library in one
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * place, but since these pieces of code are also in
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * the inner loops of output primitives, procedure call
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * overhead is out of the question.
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * See the author for a derivation if needed.
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * In scan converting polygons, we want to choose those pixels
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * which are inside the polygon. Thus, we add .5 to the starting
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * x coordinate for both left and right edges. Now we choose the
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * first pixel which is inside the pgon for the left edge and the
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * first pixel which is outside the pgon for the right edge.
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * Draw the left pixel, but not the right.
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * How to add .5 to the starting x coordinate:
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * If the edge is moving to the right, then subtract dy from the
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * error term from the general form of the algorithm.
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * If the edge is moving to the left, then add dy to the error term.
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * The reason for the difference between edges moving to the left
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * and edges moving to the right is simple: If an edge is moving
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * to the right, then we want the algorithm to flip immediately.
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * If it is moving to the left, then we don't want it to flip until
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * we traverse an entire pixel.
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync#define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) { \
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * if the edge is horizontal, then it is ignored \
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * and assumed not to be processed. Otherwise, do this stuff. \
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync if ((dy) != 0) { \
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync if (dx < 0) { \
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync#define BRESINCRPGON(d, minval, m, m1, incr1, incr2) { \
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync if (m1 > 0) { \
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync if (d > 0) { \
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync if (d >= 0) { \
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * This structure contains all of the information needed
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * to run the bresenham algorithm.
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * The variables may be hardcoded into the declarations
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * instead of using this structure to make use of
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync * register declarations.
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsynctypedef struct {
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync int d; /* decision variable */
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync#define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \
cabde247f900dcf6e58d009bbdd15099c028c6fcvboxsync BRESINITPGON(dmaj, min1, min2, bres.minor, bres.d, \