Polygon Clipping Error? - c++

Question

I have been trying to work out this problem with my Sutherland-Hodgman Polygon Clipper algorithm. When filling in the polygon i keep getting this result:
I cant seem to figure out what causing the bug, here is my code:
// #param in the number of vertices in the polygon to be clipped
// #param inV the incoming vertex list
// #param outV the outgoing vertex list
// #param ll the lower-left corner of the clipping rectangle
// #param ur the upper-right corner of the clipping rectangle
//
// #return number of vertices in the polygon resulting after clipping
int Clipper::clipPolygon( int in, const Vertex inV[], Vertex outV[],
Vertex ll, Vertex ur )
{
int out = 0, out2 = 0, out3 = 0, out4 = 0;
Vertex *outV2, *outV3, *outV4;
// We clip entire figure by clipping on the 4 edges of the clipping window
// each step will be stored, in *out pointers.
SHPC(inV, outV, in, out, ll.x, ur.y, ll.x, ll.y); // left
outV2 = new Vertex[out];
SHPC(outV, outV2, out, out2, ll.x, ll.y, ur.x, ll.y); // bottom
outV3 = new Vertex[out2];
SHPC(outV2, outV3, out2, out3, ur.x, ll.y, ur.x, ur.y); // right
outV4 = new Vertex[out3];
SHPC(outV3, outV4, out3, out4, ur.x, ur.y, ll.x, ur.y); // top
// we want outx and outy to store the final clipped polygons, which
// means we need to get content of outx4 and outy4
for (int i = 0; i < out; i++) { outV[i].x = outV4[i].x; outV[i].y = outV4[i].y; }
// same principle for out value
out = out4;
delete[] outV2;
delete[] outV3;
delete[] outV4;
return out;
}
void Clipper::SHPC(const Vertex inV[],
Vertex outV[], int in, int &out,
float x0, float y0, float x1, float y1) {
float px = inV[in - 1].x, py = inV[in - 1].y; // last vertex is the initial “predecessor”
float _x = px, _y = py;
for (int j = 0; j < in; j++) {
if (inside(inV[j].x, inV[j].y, x0, y0, x1, y1)) { // Cases 1 & 4
if (inside(px, py, x0, y0, x1, y1)) { // Case 1
output(inV[j].x, inV[j].y, out, outV);
}
else { // Case 4
intersect(px, py, inV[j].x, inV[j].y, x0, y0, x1, y1, _x, _y);
output(_x, _y, out, outV);
output(inV[j].x, inV[j].y, out, outV);
}
}
else { // Cases 2 & 3
if (inside(px, py, x0, y0, x1, y1)) { // Case 2
intersect(px, py, inV[j].x, inV[j].y, x0, y0, x1, y1, _x, _y);
output(_x, _y, out, outV);
} // Case 3 has no output
}
px = inV[j].x;
py = inV[j].y;
} // for
}
// is point inside boundary?
bool Clipper::inside(float _x, float _y, float x0, float y0, float x1, float y1) {
if (y0 == y1) { // horizontal edge
if (x0 < x1) return _y >= y0;
if (x0 > x1) return _y <= y0;
} else { // vertical edge
if (y1 > y0) return _x <= x0;
if (y0 > y1) return _x >= x0;
}
return false;
}
// put point into vector, update length
void Clipper::output(float _x, float _y, int &out, Vertex outV[]) {
outV[out].x = _x;
outV[out++].y = _y;
}
// compute intersection point, put point into newpoint parameter
void Clipper::intersect(float sx, float sy, float ex, float ey, float x0, float y0, float x1, float y1, float &_x, float &_y) {
if (x0 == x1) { // if it's a vertical edge
_x = x0;
_y = sy + (x0 - sx) * (ey - sy) / (ex - sx);
}
else { // if it's a horizontal edge
_y = y0;
_x = sx + (y0 - sy) * (ex - sx) / (ey - sy);
}
}
If I would have to guess I would say it is an issue with my inside function, but that raises the question of why is it only not working for the star and not for the rest of the shapes? I have tried rewriting the inside function, but it usually results in the same type of error only in a different direction. If anyone can point me in the right direction I would appreciate it.