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a5e7ae69e440f6816420fc99599f044e79e716b6vboxsyncfrom The Open Group.
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * Written by Brian Kelleher; Jan 1985
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * This file contains a few macros to help track
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * the edge of a filled object. The object is assumed
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * to be filled in scanline order, and thus the
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * algorithm used is an extension of Bresenham's line
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * drawing algorithm which assumes that y is always the
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * major axis.
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * Since these pieces of code are the same for any filled shape,
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * it is more convenient to gather the library in one
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * place, but since these pieces of code are also in
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * the inner loops of output primitives, procedure call
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * overhead is out of the question.
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * See the author for a derivation if needed.
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * In scan converting polygons, we want to choose those pixels
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * which are inside the polygon. Thus, we add .5 to the starting
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * x coordinate for both left and right edges. Now we choose the
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * first pixel which is inside the pgon for the left edge and the
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * first pixel which is outside the pgon for the right edge.
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * Draw the left pixel, but not the right.
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * How to add .5 to the starting x coordinate:
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * If the edge is moving to the right, then subtract dy from the
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * error term from the general form of the algorithm.
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * If the edge is moving to the left, then add dy to the error term.
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * The reason for the difference between edges moving to the left
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * and edges moving to the right is simple: If an edge is moving
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * to the right, then we want the algorithm to flip immediately.
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * If it is moving to the left, then we don't want it to flip until
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * we traverse an entire pixel.
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync#define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) { \
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * if the edge is horizontal, then it is ignored \
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * and assumed not to be processed. Otherwise, do this stuff. \
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync if ((dy) != 0) { \
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync if (dx < 0) { \
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync#define BRESINCRPGON(d, minval, m, m1, incr1, incr2) { \
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync if (m1 > 0) { \
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync if (d > 0) { \
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync if (d >= 0) { \
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * This structure contains all of the information needed
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * to run the bresenham algorithm.
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * The variables may be hardcoded into the declarations
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * instead of using this structure to make use of
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync * register declarations.
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsynctypedef struct {
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync int d; /* decision variable */
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync#define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \
a5e7ae69e440f6816420fc99599f044e79e716b6vboxsync BRESINITPGON(dmaj, min1, min2, bres.minor, bres.d, \