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b9a21c3c91c47e090316e28d759194e46628ed49vboxsyncfrom The Open Group.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * Written by Brian Kelleher; Jan 1985
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * This file contains a few macros to help track
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * the edge of a filled object. The object is assumed
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * to be filled in scanline order, and thus the
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * algorithm used is an extension of Bresenham's line
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * drawing algorithm which assumes that y is always the
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * major axis.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * Since these pieces of code are the same for any filled shape,
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * it is more convenient to gather the library in one
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * place, but since these pieces of code are also in
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * the inner loops of output primitives, procedure call
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * overhead is out of the question.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * See the author for a derivation if needed.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * In scan converting polygons, we want to choose those pixels
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * which are inside the polygon. Thus, we add .5 to the starting
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * x coordinate for both left and right edges. Now we choose the
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * first pixel which is inside the pgon for the left edge and the
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * first pixel which is outside the pgon for the right edge.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * Draw the left pixel, but not the right.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * How to add .5 to the starting x coordinate:
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * If the edge is moving to the right, then subtract dy from the
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * error term from the general form of the algorithm.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * If the edge is moving to the left, then add dy to the error term.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * The reason for the difference between edges moving to the left
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * and edges moving to the right is simple: If an edge is moving
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * to the right, then we want the algorithm to flip immediately.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * If it is moving to the left, then we don't want it to flip until
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * we traverse an entire pixel.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync#define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) { \
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * if the edge is horizontal, then it is ignored \
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * and assumed not to be processed. Otherwise, do this stuff. \
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync if ((dy) != 0) { \
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync if (dx < 0) { \
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync#define BRESINCRPGON(d, minval, m, m1, incr1, incr2) { \
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync if (m1 > 0) { \
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync if (d > 0) { \
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync if (d >= 0) { \
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * This structure contains all of the information needed
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * to run the bresenham algorithm.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * The variables may be hardcoded into the declarations
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * instead of using this structure to make use of
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * register declarations.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsynctypedef struct {
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync int d; /* decision variable */
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync#define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync BRESINITPGON(dmaj, min1, min2, bres.minor, bres.d, \