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302abf53d2b1a686f6eafd445c49e1e006afb190bnicholesdocumentation.
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302abf53d2b1a686f6eafd445c49e1e006afb190bnicholesfrom The Open Group.
9558e9fdb620dd6f42ca93beac6c3ab734086706bnicholes * Written by Brian Kelleher; Jan 1985
9558e9fdb620dd6f42ca93beac6c3ab734086706bnicholes * This file contains a few macros to help track
9558e9fdb620dd6f42ca93beac6c3ab734086706bnicholes * the edge of a filled object. The object is assumed
9558e9fdb620dd6f42ca93beac6c3ab734086706bnicholes * to be filled in scanline order, and thus the
9558e9fdb620dd6f42ca93beac6c3ab734086706bnicholes * algorithm used is an extension of Bresenham's line
9558e9fdb620dd6f42ca93beac6c3ab734086706bnicholes * drawing algorithm which assumes that y is always the
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * major axis.
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * Since these pieces of code are the same for any filled shape,
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * it is more convenient to gather the library in one
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * place, but since these pieces of code are also in
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * the inner loops of output primitives, procedure call
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * overhead is out of the question.
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * See the author for a derivation if needed.
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * In scan converting polygons, we want to choose those pixels
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * which are inside the polygon. Thus, we add .5 to the starting
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * x coordinate for both left and right edges. Now we choose the
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * first pixel which is inside the pgon for the left edge and the
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * first pixel which is outside the pgon for the right edge.
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * Draw the left pixel, but not the right.
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * How to add .5 to the starting x coordinate:
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * If the edge is moving to the right, then subtract dy from the
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * error term from the general form of the algorithm.
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * If the edge is moving to the left, then add dy to the error term.
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * The reason for the difference between edges moving to the left
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * and edges moving to the right is simple: If an edge is moving
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * to the right, then we want the algorithm to flip immediately.
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * If it is moving to the left, then we don't want it to flip until
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * we traverse an entire pixel.
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes#define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) { \
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * if the edge is horizontal, then it is ignored \
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * and assumed not to be processed. Otherwise, do this stuff. \
ac7985784d08a3655291f24f711812b4d8b1cbcffuankg if ((dy) != 0) { \
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes if (dx < 0) { \
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes#define BRESINCRPGON(d, minval, m, m1, incr1, incr2) { \
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes if (m1 > 0) { \
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes if (d > 0) { \
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes if (d >= 0) { \
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * This structure contains all of the information needed
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * to run the bresenham algorithm.
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * The variables may be hardcoded into the declarations
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * instead of using this structure to make use of
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes * register declarations.
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholestypedef struct {
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes int d; /* decision variable */
302abf53d2b1a686f6eafd445c49e1e006afb190bnicholes#define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \