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#include "Vlib.h"
VPolygon *
_VClipPolygon(VPolygon * poly, VPoint * clipPlane)
{
register int j, lastj, numPts = 0, clipped = 0;
double d1, d2, a;
VPoint tmpPoint[VmaxVP];
VPolygon *p;
if (poly->numVtces > 0) {
lastj = poly->numVtces - 1;
d1 = VDotProd(&(poly->vertex[poly->numVtces - 1]), clipPlane);
numPts = 0;
/*
* Examine each vertex and determine if it is inside or outside of the
* specified clipping plane.
*/
for (j = 0; j < poly->numVtces; ++j) {
/* Leading vertex inside? */
if (d1 > 0.0)
tmpPoint[numPts++] = poly->vertex[lastj];
d2 = VDotProd(&(poly->vertex[j]), clipPlane);
/* Does the edge straddle the window? If so, add a vertex on the window */
if (d1 * d2 < 0.0) {
clipped = 1;
a = d1 / (d1 - d2);
tmpPoint[numPts].x = a * poly->vertex[j].x +
(1.0 - a) * poly->vertex[lastj].x;
tmpPoint[numPts].y = a * poly->vertex[j].y +
(1.0 - a) * poly->vertex[lastj].y;
tmpPoint[numPts++].z = a * poly->vertex[j].z +
(1.0 - a) * poly->vertex[lastj].z;
}
lastj = j;
d1 = d2;
}
}
/*
* If the polygon was completely out of bounds, delete this polygon.
*/
if (numPts == 0) {
p = (VPolygon *) NULL;
VDestroyPolygon(poly);
#ifdef DEBUG
fprintf(stderr, "VClipPolygon: polygon outside area of interest\n");
#endif
}
/*
* If we did any clipping, return the clipped polygon.
*/
else if (clipped) {
p = VCreatePolygonFromTemplate(numPts, tmpPoint, poly);
#ifdef DEBUG
fprintf(stderr, "VClipPolygon: Polygon has been clipped:\n");
fprintf(stderr, "Before Clipping:\n");
VPrintPolygon(stderr, poly);
fprintf(stderr, "\nAfter Clipping:\n\n");
VPrintPolygon(stderr, p);
#endif
VDestroyPolygon(poly);
}
else
p = poly;
return p;
}
VPolygon *
VClipPolygon(VPolygon * poly, VPolygon * clipPoly)
{
int i;
VPolygon *p = poly;
/*
* Clip against each clipping plane supplied, one at a time.
*/
for (i = 0; i < clipPoly->numVtces; ++i) {
if (p == (VPolygon *) NULL)
break;
p = _VClipPolygon(p, &(clipPoly->vertex[i]));
}
return p;
}
VPolygon * /*ARGSUSED */
VClipSidedPolygon(Viewport * v, VPolygon * poly, VPolygon * clipPoly)
{
int i;
VPolygon *p = poly;
if (p->flags & PolyNormalValid) {
if (VDotProd(&p->vertex[0], &p->normal) >= 0.0) {
if (p->backColor) {
p->flags |= PolyUseBackColor;
}
else if (p->flags & PolyClipBackface) {
VDestroyPolygon(p);
return (VPolygon *) NULL;
}
}
else {
p->flags &= ~(PolyUseBackColor);
}
}
/*
* Clip against each clipping plane supplied, one at a time.
*/
for (i = 0; i < clipPoly->numVtces; ++i) {
if (p == (VPolygon *) NULL)
break;
p = _VClipPolygon(p, &(clipPoly->vertex[i]));
}
return p;
}
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