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b9a21c3c91c47e090316e28d759194e46628ed49vboxsyncfrom The Open Group.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * Created by Brian Kelleher; Oct 1985
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * Include file for filled polygon routines.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * These are the data structures needed to scan
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * convert regions. Two different scan conversion
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * methods are available -- the even-odd method, and
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * the winding number method.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * The even-odd rule states that a point is inside
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * the polygon if a ray drawn from that point in any
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * direction will pass through an odd number of
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * path segments.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * By the winding number rule, a point is decided
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * to be inside the polygon if a ray drawn from that
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * point in any direction passes through a different
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * number of clockwise and counter-clockwise path
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * segments.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * These data structures are adapted somewhat from
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * the algorithm in (Foley/Van Dam) for scan converting
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * polygons.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * The basic algorithm is to start at the top (smallest y)
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * of the polygon, stepping down to the bottom of
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * the polygon by incrementing the y coordinate. We
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * keep a list of edges which the current scanline crosses,
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * sorted by x. This list is called the Active Edge Table (AET)
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * As we change the y-coordinate, we update each entry in
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * in the active edge table to reflect the edges new xcoord.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * This list must be sorted at each scanline in case
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * two edges intersect.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * We also keep a data structure known as the Edge Table (ET),
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * which keeps track of all the edges which the current
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * scanline has not yet reached. The ET is basically a
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * list of ScanLineList structures containing a list of
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * edges which are entered at a given scanline. There is one
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * ScanLineList per scanline at which an edge is entered.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * When we enter a new edge, we move it from the ET to the AET.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * From the AET, we can implement the even-odd rule as in
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * The winding number rule is a little trickier. We also
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * keep the EdgeTableEntries in the AET linked by the
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * nextWETE (winding EdgeTableEntry) link. This allows
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * the edges to be linked just as before for updating
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * purposes, but only uses the edges linked by the nextWETE
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * link as edges representing spans of the polygon to
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * drawn (as with the even-odd rule).
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * for the winding number rule
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync BRESINFO bres; /* Bresenham info to run the edge */
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync struct _EdgeTableEntry *next; /* next in the list */
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync struct _EdgeTableEntry *back; /* for insertion sort */
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync struct _EdgeTableEntry *nextWETE; /* for winding num rule */
b9a21c3c91c47e090316e28d759194e46628ed49vboxsynctypedef struct {
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * Here is a struct to help with storage allocation
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * so we can allocate a big chunk at a time, and then take
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * pieces from this heap when we need to.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * number of points to buffer before sending them off
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * to scanlines() : Must be an even number
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * a few macros for the inner loops of the fill code where
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * performance considerations don't allow a procedure call.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * Evaluate the given edge at the given scanline.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * If the edge has expired, then we leave it and fix up
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * the active edge table; otherwise, we increment the
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * x value to be ready for the next scanline.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * The winding number rule is in effect, so we must notify
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * the caller when the edge has been removed so he
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * can reorder the Winding Active Edge Table.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync#define EVALUATEEDGEWINDING(pAET, pPrevAET, y, fixWAET) { \
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * Evaluate the given edge at the given scanline.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * If the edge has expired, then we leave it and fix up
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * the active edge table; otherwise, we increment the
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * x value to be ready for the next scanline.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync * The even-odd rule is in effect.
b9a21c3c91c47e090316e28d759194e46628ed49vboxsync int /*count*/,