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61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * Written by Brian Kelleher; Jan 1985
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * This file contains a few macros to help track
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * the edge of a filled object. The object is assumed
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * to be filled in scanline order, and thus the
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * algorithm used is an extension of Bresenham's line
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * drawing algorithm which assumes that y is always the
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * major axis.
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * Since these pieces of code are the same for any filled shape,
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * it is more convenient to gather the library in one
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * place, but since these pieces of code are also in
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * the inner loops of output primitives, procedure call
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * overhead is out of the question.
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * See the author for a derivation if needed.
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * In scan converting polygons, we want to choose those pixels
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * which are inside the polygon. Thus, we add .5 to the starting
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * x coordinate for both left and right edges. Now we choose the
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * first pixel which is inside the pgon for the left edge and the
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * first pixel which is outside the pgon for the right edge.
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * Draw the left pixel, but not the right.
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * How to add .5 to the starting x coordinate:
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * If the edge is moving to the right, then subtract dy from the
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * error term from the general form of the algorithm.
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * If the edge is moving to the left, then add dy to the error term.
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * The reason for the difference between edges moving to the left
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * and edges moving to the right is simple: If an edge is moving
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * to the right, then we want the algorithm to flip immediately.
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * If it is moving to the left, then we don't want it to flip until
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * we traverse an entire pixel.
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync#define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) { \
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * if the edge is horizontal, then it is ignored \
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * and assumed not to be processed. Otherwise, do this stuff. \
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync if ((dy) != 0) { \
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync if (dx < 0) { \
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync#define BRESINCRPGON(d, minval, m, m1, incr1, incr2) { \
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync if (m1 > 0) { \
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync if (d > 0) { \
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync if (d >= 0) { \
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * This structure contains all of the information needed
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * to run the bresenham algorithm.
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * The variables may be hardcoded into the declarations
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * instead of using this structure to make use of
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync * register declarations.
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsynctypedef struct {
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync int d; /* decision variable */
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync#define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \
61cb83a8ccd1dd7f671f31fa93c9d8b7be09b4ccvboxsync BRESINITPGON(dmaj, min1, min2, bres.minor, bres.d, \