gtk/gdk/linux-fb/mifpolycon.c

/***********************************************************

Copyright 1987, 1998  The Open Group

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Copyright 1987 by Digital Equipment Corporation, Maynard, Massachusetts.

                        All Rights Reserved

Permission to use, copy, modify, and distribute this software and its 
documentation for any purpose and without fee is hereby granted, 
provided that the above copyright notice appear in all copies and that
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******************************************************************/
/* $TOG: mifpolycon.c /main/13 1998/02/09 14:47:05 kaleb $ */
#include <config.h>
#include <math.h>
#include "mi.h"
#include "mifpoly.h"

static int
GetFPolyYBounds(register SppPointPtr pts, int n, double yFtrans, int *by, int *ty);

#ifdef ICEILTEMPDECL
ICEILTEMPDECL
#endif

/*
 *	Written by Todd Newman; April. 1987.
 *
 *	Fill a convex polygon.  If the given polygon
 *	is not convex, then the result is undefined.
 *	The algorithm is to order the edges from smallest
 *	y to largest by partitioning the array into a left
 *	edge list and a right edge list.  The algorithm used
 *	to traverse each edge is digital differencing analyzer
 *	line algorithm with y as the major axis. There's some funny linear
 *	interpolation involved because of the subpixel postioning.
 */
void
miFillSppPoly(GdkDrawable *dst, GdkGC *pgc, int count, SppPointPtr ptsIn, int xTrans, int yTrans, double xFtrans, double yFtrans)
#if 0
    GdkDrawable* 	dst;
    GdkGC*		pgc;
    int			count;          /* number of points */
    SppPointPtr 	ptsIn;          /* the points */
    int			xTrans, yTrans;	/* Translate each point by this */
    double		xFtrans, yFtrans;	/* translate before conversion
    						   by this amount.  This provides
						   a mechanism to match rounding
						   errors with any shape that must
						   meet the polygon exactly.
						 */
#endif
{
    double		xl = 0.0, xr = 0.0,	/* x vals of left and right edges */
          		ml = 0.0,       /* left edge slope */
          		mr = 0.0,       /* right edge slope */
          		dy,             /* delta y */
    			i;              /* loop counter */
    int			y,              /* current scanline */
    			j,
    			imin,           /* index of vertex with smallest y */
    			ymin,           /* y-extents of polygon */
    			ymax,
    	 		*Marked;	/* set if this vertex has been used */
    register int	left, right,	/* indices to first endpoints */
    			nextleft,
                 	nextright;	/* indices to second endpoints */
    GdkSpan*    	ptsOut,
      *FirstPoint;	/* output buffer */

    imin = GetFPolyYBounds(ptsIn, count, yFtrans, &ymin, &ymax);

    y = ymax - ymin + 1;
    if ((count < 3) || (y <= 0))
	return;
    ptsOut = FirstPoint = (GdkSpan*)ALLOCATE_LOCAL(sizeof(GdkSpan) * y);
    Marked = (int *) ALLOCATE_LOCAL(sizeof(int) * count);

    if(!ptsOut || !Marked)
    {
	if (Marked) DEALLOCATE_LOCAL(Marked);
	if (ptsOut) DEALLOCATE_LOCAL(ptsOut);
	return;
    }

    for(j = 0; j < count; j++)
	Marked[j] = 0;
    nextleft = nextright = imin;
    Marked[imin] = -1;
    y = ICEIL(ptsIn[nextleft].y + yFtrans);

    /*
     *  loop through all edges of the polygon
     */
    do
    {
        /* add a left edge if we need to */
        if ((y > (ptsIn[nextleft].y + yFtrans) ||
 	     ISEQUAL(y, ptsIn[nextleft].y + yFtrans)) &&
	     Marked[nextleft] != 1)
	{
	    Marked[nextleft]++;
            left = nextleft++;

            /* find the next edge, considering the end conditions */
            if (nextleft >= count)
                nextleft = 0;

            /* now compute the starting point and slope */
	    dy = ptsIn[nextleft].y - ptsIn[left].y;
	    if (dy != 0.0)
	    { 
		ml = (ptsIn[nextleft].x - ptsIn[left].x) / dy;
		dy = y - (ptsIn[left].y + yFtrans);
		xl = (ptsIn[left].x + xFtrans) + ml * MAX(dy, 0); 
	    }
        }

        /* add a right edge if we need to */
        if ((y > ptsIn[nextright].y + yFtrans) ||
 	     (ISEQUAL(y, ptsIn[nextright].y + yFtrans)
	      && Marked[nextright] != 1))
	{
	    Marked[nextright]++;
            right = nextright--;

            /* find the next edge, considering the end conditions */
            if (nextright < 0)
                nextright = count - 1;

            /* now compute the starting point and slope */
	    dy = ptsIn[nextright].y - ptsIn[right].y;
	    if (dy != 0.0) 
	    { 
		mr = (ptsIn[nextright].x - ptsIn[right].x) / dy;
		dy = y - (ptsIn[right].y + yFtrans); 
		xr = (ptsIn[right].x + xFtrans) + mr * MAX(dy, 0);
	    }
        }


        /*
         *  generate scans to fill while we still have
         *  a right edge as well as a left edge.
         */
        i = (MIN(ptsIn[nextleft].y, ptsIn[nextright].y) + yFtrans) - y;

	if (i < EPSILON)
	{
	    if(Marked[nextleft] && Marked[nextright])
	    {
	        /* Arrgh, we're trapped! (no more points) 
	         * Out, we've got to get out of here before this decadence saps
	         * our will completely! */
	        break;
	    }
	    continue;
	}
	else
	{
		j = (int) i;
		if(!j)
		    j++;
	}
        while (j > 0) 
        {
	    int cxl, cxr;

            ptsOut->y = (y) + yTrans;

	    cxl = ICEIL(xl);
	    cxr = ICEIL(xr);
            /* reverse the edges if necessary */
            if (xl < xr) 
            {
	      ptsOut->width = cxr - cxl;
	      (ptsOut++)->x = cxl + xTrans;
            }
            else 
            {
	      ptsOut->width = cxl - cxr;
	      (ptsOut++)->x = cxr + xTrans;
            }
            y++;

            /* increment down the edges */
	    xl += ml;
	    xr += mr;
	    j--;
        }
    }  while (y <= ymax);

    /* Finally, fill the spans we've collected */
    gdk_fb_fill_spans(dst, pgc, FirstPoint, ptsOut-FirstPoint, TRUE);
    DEALLOCATE_LOCAL(Marked);
    DEALLOCATE_LOCAL(FirstPoint);
}


/* Find the index of the point with the smallest y.also return the
 * smallest and largest y */
static int
GetFPolyYBounds(register SppPointPtr pts, int n, double yFtrans, int *by, int *ty)
{
    register SppPointPtr	ptMin;
    double 			ymin, ymax;
    SppPointPtr			ptsStart = pts;

    ptMin = pts;
    ymin = ymax = (pts++)->y;

    while (--n > 0) {
        if (pts->y < ymin)
	{
            ptMin = pts;
            ymin = pts->y;
        }
	if(pts->y > ymax)
            ymax = pts->y;

        pts++;
    }

    *by = ICEIL(ymin + yFtrans);
    *ty = ICEIL(ymax + yFtrans - 1);
    return(ptMin-ptsStart);
}