/* $TOG: poly.h /main/5 1998/02/06 17:47:27 kaleb $ */

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/*

 *     This file contains a few macros to help track

 *     the edge of a filled object.  The object is assumed

 *     to be filled in scanline order, and thus the

 *     algorithm used is an extension of Bresenham's line

 *     drawing algorithm which assumes that y is always the

 *     major axis.

 *     Since these pieces of code are the same for any filled shape,

 *     it is more convenient to gather the library in one

 *     place, but since these pieces of code are also in

 *     the inner loops of output primitives, procedure call

 *     overhead is out of the question.

 *     See the author for a derivation if needed.

 */

/*

 *  In scan converting polygons, we want to choose those pixels

 *  which are inside the polygon.  Thus, we add .5 to the starting

 *  x coordinate for both left and right edges.  Now we choose the

 *  first pixel which is inside the pgon for the left edge and the

 *  first pixel which is outside the pgon for the right edge.

 *  Draw the left pixel, but not the right.

 *

 *  How to add .5 to the starting x coordinate:

 *      If the edge is moving to the right, then subtract dy from the

 *  error term from the general form of the algorithm.

 *      If the edge is moving to the left, then add dy to the error term.

 *

 *  The reason for the difference between edges moving to the left

 *  and edges moving to the right is simple:  If an edge is moving

 *  to the right, then we want the algorithm to flip immediately.

 *  If it is moving to the left, then we don't want it to flip until

 *  we traverse an entire pixel.

 */

#define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) { \

    int dx;      /* local storage */ \

\

    /* \

     *  if the edge is horizontal, then it is ignored \

     *  and assumed not to be processed.  Otherwise, do this stuff. \

     */ \

    if ((dy) != 0) { \

        xStart = (x1); \

        dx = (x2) - xStart; \

        if (dx < 0) { \

            m = dx / (dy); \

            m1 = m - 1; \

            incr1 = -2 * dx + 2 * (dy) * m1; \

            incr2 = -2 * dx + 2 * (dy) * m; \

            d = 2 * m * (dy) - 2 * dx - 2 * (dy); \

        } else { \

            m = dx / (dy); \

            m1 = m + 1; \

            incr1 = 2 * dx - 2 * (dy) * m1; \

            incr2 = 2 * dx - 2 * (dy) * m; \

            d = -2 * m * (dy) + 2 * dx; \

        } \

    } \

}

#define BRESINCRPGON(d, minval, m, m1, incr1, incr2) { \

    if (m1 > 0) { \

        if (d > 0) { \

            minval += m1; \

            d += incr1; \

        } \

        else { \

            minval += m; \

            d += incr2; \

        } \

    } else {\

        if (d >= 0) { \

            minval += m1; \

            d += incr1; \

        } \

        else { \

            minval += m; \

            d += incr2; \

        } \

    } \

}

/*

 *     This structure contains all of the information needed

 *     to run the bresenham algorithm.

 *     The variables may be hardcoded into the declarations

 *     instead of using this structure to make use of

 *     register declarations.

 */

typedef struct {

    int minor_axis;	/* minor axis        */

    int d;		/* decision variable */

    int m, m1;		/* slope and slope+1 */

    int incr1, incr2;	/* error increments */

} BRESINFO;

#define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \

	BRESINITPGON(dmaj, min1, min2, bres.minor_axis, bres.d, \

                     bres.m, bres.m1, bres.incr1, bres.incr2)

#define BRESINCRPGONSTRUCT(bres) \

        BRESINCRPGON(bres.d, bres.minor_axis, bres.m, bres.m1, bres.incr1, bres.incr2)

/*

 *     These are the data structures needed to scan

 *     convert regions.  Two different scan conversion

 *     methods are available -- the even-odd method, and

 *     the winding number method.

 *     The even-odd rule states that a point is inside

 *     the polygon if a ray drawn from that point in any

 *     direction will pass through an odd number of

 *     path segments.

 *     By the winding number rule, a point is decided

 *     to be inside the polygon if a ray drawn from that

 *     point in any direction passes through a different

 *     number of clockwise and counter-clockwise path

 *     segments.

 *

 *     These data structures are adapted somewhat from

 *     the algorithm in (Foley/Van Dam) for scan converting

 *     polygons.

 *     The basic algorithm is to start at the top (smallest y)

 *     of the polygon, stepping down to the bottom of

 *     the polygon by incrementing the y coordinate.  We

 *     keep a list of edges which the current scanline crosses,

 *     sorted by x.  This list is called the Active Edge Table (AET)

 *     As we change the y-coordinate, we update each entry in 

 *     in the active edge table to reflect the edges new xcoord.

 *     This list must be sorted at each scanline in case

 *     two edges intersect.

 *     We also keep a data structure known as the Edge Table (ET),

 *     which keeps track of all the edges which the current

 *     scanline has not yet reached.  The ET is basically a

 *     list of ScanLineList structures containing a list of

 *     edges which are entered at a given scanline.  There is one

 *     ScanLineList per scanline at which an edge is entered.

 *     When we enter a new edge, we move it from the ET to the AET.

 *

 *     From the AET, we can implement the even-odd rule as in

 *     (Foley/Van Dam).

 *     The winding number rule is a little trickier.  We also

 *     keep the EdgeTableEntries in the AET linked by the

 *     nextWETE (winding EdgeTableEntry) link.  This allows

 *     the edges to be linked just as before for updating

 *     purposes, but only uses the edges linked by the nextWETE

 *     link as edges representing spans of the polygon to

 *     drawn (as with the even-odd rule).

 */

/*

 * for the winding number rule

 */

#define CLOCKWISE          1

#define COUNTERCLOCKWISE  -1 

typedef struct _EdgeTableEntry {

     int ymax;             /* ycoord at which we exit this edge. */

     BRESINFO bres;        /* Bresenham info to run the edge     */

     struct _EdgeTableEntry *next;       /* next in the list     */

     struct _EdgeTableEntry *back;       /* for insertion sort   */

     struct _EdgeTableEntry *nextWETE;   /* for winding num rule */

     int ClockWise;        /* flag for winding number rule       */

} EdgeTableEntry;

typedef struct _ScanLineList{

     int scanline;              /* the scanline represented */

     EdgeTableEntry *edgelist;  /* header node              */

     struct _ScanLineList *next;  /* next in the list       */

} ScanLineList;

typedef struct {

     int ymax;                 /* ymax for the polygon     */

     int ymin;                 /* ymin for the polygon     */

     ScanLineList scanlines;   /* header node              */

} EdgeTable;

/*

 * Here is a struct to help with storage allocation

 * so we can allocate a big chunk at a time, and then take

 * pieces from this heap when we need to.

 */

#define SLLSPERBLOCK 25

typedef struct _ScanLineListBlock {

     ScanLineList SLLs[SLLSPERBLOCK];

     struct _ScanLineListBlock *next;

} ScanLineListBlock;

/*

 *

 *     a few macros for the inner loops of the fill code where

 *     performance considerations don't allow a procedure call.

 *

 *     Evaluate the given edge at the given scanline.

 *     If the edge has expired, then we leave it and fix up

 *     the active edge table; otherwise, we increment the

 *     x value to be ready for the next scanline.

 *     The winding number rule is in effect, so we must notify

 *     the caller when the edge has been removed so he

 *     can reorder the Winding Active Edge Table.

 */

#define EVALUATEEDGEWINDING(pAET, pPrevAET, y, fixWAET) { \

   if (pAET->ymax == y) {          /* leaving this edge */ \

      pPrevAET->next = pAET->next; \

      pAET = pPrevAET->next; \

      fixWAET = 1; \

      if (pAET) \

         pAET->back = pPrevAET; \

   } \

   else { \

      BRESINCRPGONSTRUCT(pAET->bres); \

      pPrevAET = pAET; \

      pAET = pAET->next; \

   } \

}

/*

 *     Evaluate the given edge at the given scanline.

 *     If the edge has expired, then we leave it and fix up

 *     the active edge table; otherwise, we increment the

 *     x value to be ready for the next scanline.

 *     The even-odd rule is in effect.

 */

#define EVALUATEEDGEEVENODD(pAET, pPrevAET, y) { \

   if (pAET->ymax == y) {          /* leaving this edge */ \

      pPrevAET->next = pAET->next; \

      pAET = pPrevAET->next; \

      if (pAET) \

         pAET->back = pPrevAET; \

   } \

   else { \

      BRESINCRPGONSTRUCT(pAET->bres); \

      pPrevAET = pAET; \

      pAET = pAET->next; \

   } \

}