/*
 * cvhhwdiff.c		Jim Piper	22-09-86
 *
 * Compute difference in area between a profile and its convex hull,
 * weighted by the cosine of the angle which the convex hull arc
 * makes to the horizontal (notionally; computation differs in detail
 * due to scaling problems between horizontal and value axes).
 */

#include <stdio.h>
#include <wstruct.h>


cvhhwdiff (cvhh,cprof)
struct object *cvhh, *cprof;
{
	register int i,j,cdiff,xdiff,ydiff,*hv;
	int xrange,yrange,wdiff;
	struct polygondomain *cvhpdom;
	struct histogramdomain *cprofhdom;
	register struct ivertex *vtx, *wtx;

	cvhpdom = (struct polygondomain *) cvhh->idom;
	vtx = cvhpdom->vtx;
	cprofhdom = (struct histogramdomain *) cprof->idom;
	hv = cprofhdom->hv;
	/*
	 * compute x and y ranges of convex hull
	 */
	xrange = vtx[cvhpdom->nvertices - 1].vtX - vtx->vtX;
	yrange = 0;
	for (i=0; i<cvhpdom->nvertices; i++,vtx++)
		if (vtx->vtY > yrange)
			yrange = vtx->vtY;

	/*
	 * advance hv to first non-zero point
	 */
	while (*hv == 0)
		hv++;
	wdiff = 0;
	vtx = cvhpdom->vtx;
	wtx = vtx+1;
	for (i=1; i<cvhpdom->nvertices; i++,vtx++,wtx++) {
		/* compute (twice) area under chord */
		xdiff = wtx->vtX - vtx->vtX;
		cdiff = xdiff * (wtx->vtY+vtx->vtY);
		/* subtract (twice) area of profile segment under this chord */
		cdiff -= *hv++;		/* half-weight from first point */
					/* full weight from non-end points */
		for (j=vtx->vtX+1; j<wtx->vtX; j++)
			cdiff -=  2 * *hv++;
		cdiff -= *hv;		/* half-weight from last point */
		/*
		 * scale xdiff, ydiff.
		 */
		xdiff *= yrange;
		ydiff = wtx->vtY - vtx->vtY;
		if (ydiff < 0)
			ydiff = - ydiff;
		ydiff *= xrange;
		/*
		 * weight by |xdiff/(xdiff + ydiff)|
		 */
		cdiff = cdiff * xdiff / (xdiff + ydiff);
		wdiff += cdiff;
	}
	return(wdiff);
}