// Generates a new polygon by dragging a polygon through an angle, and taking all the points it
// touched (and a few extras for overestimation)
// Only valid for convex polygons, and small rotations (20 degrees or less)
// stroke from theta1 to theta2
public static Polygon strokeRot(double theta1, double theta2, Polygon poly) {
Polygon poly1 = mul(Mat.rotation(theta1), poly);
Polygon poly2 = mul(Mat.rotation(theta2), poly);
Polygon stroked = combine(poly1, poly2);
ArrayList<Mat> cornerVerts;
Polygon corner;
int thisVertex, prevVertex, nextVertex;
Mat origin = Mat.encodePoint(0, 0);
Mat cornerVert1a, cornerVert1b;
Mat cornerVert2a, cornerVert2b;
double actualDist, desiredDist;
Mat cornerTransform;
for (thisVertex = 0; thisVertex < poly.vertices.size(); thisVertex++) {
if (thisVertex == 0) {
prevVertex = poly.vertices.size() - 1;
} else {
prevVertex = thisVertex - 1;
}
if (thisVertex == poly.vertices.size() - 1) {
nextVertex = 0;
} else {
nextVertex = thisVertex + 1;
}
cornerVerts = new ArrayList<Mat>();
cornerVerts.add(poly2.vertices.get(nextVertex));
cornerVerts.add(origin);
cornerVerts.add(poly1.vertices.get(prevVertex));
cornerVert1a = poly1.vertices.get(thisVertex);
cornerVert2a = poly2.vertices.get(thisVertex);
actualDist = ptSegDistance(cornerVert1a, cornerVert2a, origin);
desiredDist = Mat.dist(cornerVert1a, Mat.encodePoint(0, 0));
cornerTransform = Mat.mul(desiredDist / actualDist, Mat.eye(4));
cornerVert1b = Mat.mul(cornerTransform, cornerVert1a);
cornerVert2b = Mat.mul(cornerTransform, cornerVert2a);
cornerVert1b =
lineSegIntersection(
cornerVert1b, cornerVert2b, poly1.vertices.get(prevVertex), cornerVert1a);
cornerVert2b =
lineSegIntersection(
cornerVert1b, cornerVert2b, poly2.vertices.get(nextVertex), cornerVert2a);
cornerVerts.add(cornerVert1b);
cornerVerts.add(cornerVert2b);
corner = new Polygon(cornerVerts);
stroked = combine(stroked, corner);
}
return stroked;
}
public static double ptSegDistance(Mat e0, Mat e1, Mat p) {
double x0 = e0.data[0][0];
double y0 = e0.data[1][0];
double x1 = e1.data[0][0];
double y1 = e1.data[1][0];
double xp = p.data[0][0];
double yp = p.data[1][0];
e0 = new Mat(2, 1);
e0.data[0][0] = x0;
e0.data[1][0] = y0;
e1 = new Mat(2, 1);
e1.data[0][0] = x1;
e1.data[1][0] = y1;
p = new Mat(2, 1);
p.data[0][0] = xp;
p.data[1][0] = yp;
e1 = Mat.sub(e1, e0);
p = Mat.sub(p, e0);
e0.data[0][0] = 0;
e0.data[1][0] = 0;
Mat e0b = Mat.sub(e0, e1);
Mat pb = Mat.sub(p, e1);
Mat e1b = new Mat(2, 1);
e1b.data[0][0] = 0;
e1b.data[1][0] = 0;
if (Mat.dot(e1, p) > 0) {
if (Mat.dot(e0b, pb) > 0) {
Mat e1u = Mat.mul(1 / Mat.l2(e1), e1);
return Mat.dist(p, Mat.mul(Mat.dot(e1u, p), e1u));
} else {
return Mat.dist(p, e1);
}
} else {
return Mat.dist(p, e0);
}
}
public static boolean ptsEqual(Mat p0, Mat p1, double tolerance) {
return tolerance > Mat.dist(p0, p1);
}