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# splitting polygons

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hi.. using following function to split a polygon, however, it appears to occasionally create erroneous output when splitting many-sided polygons (all of which are convex) //split a polygon by a plane void split(PLANE3D &partition, POLYGON3D &front, POLYGON3D &back) { //number of points in two resulting polygons int out_c = 0, in_c = 0; //two temporary points for testing VERTEX3D ptA, ptB; //points in resulting polygons VERTEX3D outpts[64], inpts[64]; //two distances from the plane for ptA & ptB double sideA, sideB; //ensure points in polygon are sorted before splitting sort(); //store ptA ptA = points[count - 1]; //calculate distance from plane of ptA sideA = partition.distance(ptA); //loop through all the points for (short i = -1; ++i < count { //store ptB distance from partition ptB = points; sideB = partition.distance(ptB); //test where the two ponits lie if (sideB > EPSILON) { //test sideA if (sideA < -EPSILON) { //compute intersection point of line //from ptA to ptB with the partition. VECTOR3D v = ptB - ptA; double sect = - partition.distance(ptA) / (partition.normal().dotProduct(v)); VERTEX3D add(ptA.x + (v.x * sect), ptA.y + (v.y * sect), ptA.z + (v.z * sect)); //add the point outpts[out_c++] = inpts[in_c++] = add; } outpts[out_c++] = ptB; } //test sideB else if (sideB < -EPSILON) { //test sideA if (sideA > EPSILON) { //compute intersection point of line //from ptA to ptB with the partition. VECTOR3D v = ptB - ptA; double sect = - partition.distance(ptA) / (partition.normal().dotProduct(v)); VERTEX3D add(ptA.x + (v.x * sect), ptA.y + (v.y * sect), ptA.z + (v.z * sect)); //add the point outpts[out_c++] = inpts[in_c++] = add; } inpts[in_c++] = ptB; } //line is on plane else { outpts[out_c++] = inpts[in_c++] = ptB; } ptA = ptB; sideA = sideB; } //create new polygons front = POLYGON3D(outpts, out_c); front.plane = plane; sort(); back = POLYGON3D(inpts, in_c); back.plane = plane; sort(); } can anyone spot any glaring mistakes? cheers in advance

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You might want to take out the smiley face from your code. My compiler always barfs at me when I put smileys in.

error C2142: emoticon error : Programmer too happy

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