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#include <Alib.h>
#define IsInside(w, pt) pt.x < w->clip.x1 || pt.x >= w->clip.x2 || \
pt.y < w->clip.y1 || pt.y >= w->clip.y2
/*
* A quick and dirty 2D polygon clipping algorithm.
*/
void
Clip2DPolygon(AWindow * w, Point * pts, int npts, Point * clippedPts, int *nClippedPts)
{
register int numPts, j, lastj, inside, lastInside;
int x1, y1, x2, y2;
lastj = npts - 1;
numPts = 0;
lastInside = IsInside(w, pts[lastj]) ? 1 : 0;
for (j = 0; j < npts; ++j) {
if (lastInside == 1) {
clippedPts[numPts++] = pts[lastj];
}
inside = (IsInside(w, pts[j])) ? 1 : 0;
/*
* Fast, but not accurate. This method does not handle polygons in corners
* well. A more accurate method would be to clip by each edge independently.
*/
if ((inside ^ lastInside) == 1) {
x1 = pts[lastj].x;
y1 = pts[lastj].y;
x2 = pts[j].x;
y2 = pts[j].y;
ClipLine(w, &x1, &y1, &x2, &y2);
if (x2 == pts[lastj].x && y2 == pts[lastj].y) {
clippedPts[numPts].x = x1;
clippedPts[numPts++].y = y1;
}
else {
clippedPts[numPts].x = x2;
clippedPts[numPts++].y = y2;
}
}
lastInside = inside;
lastj = j;
}
*nClippedPts = numPts;
}
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