offset.java

PVector[] offsetCurve(PVector[] crv, float dist) {
  PVector[] offset = new PVector[crv.length];
  for(int i=1;i<offset.length-1;++i) {
    PVector currPt = crv[i];
    PVector prevPt = crv[i-1];
    PVector nextPt = crv[i+1];
    PVector v1 = PVector.sub(prevPt,currPt);
    PVector v2 = PVector.sub(nextPt,currPt);
    v2.normalize();
    v1.normalize();
    
    float angle = PVector.angleBetween(v1,v2);
    PVector bisector;
    if(angle < .0001) {
      bisector = new PVector(-v2.y,v2.x); //rotate 90 degrees.
      bisector.mult(dist);
    } else {
      angle /= 2.0;
      float sinA = sin(angle);
      float cosA = cos(angle);
      bisector = PVector.add(v1,v2);
      bisector.normalize();
      bisector.mult(-Math.signum(v1.x*v2.y-v2.x*v1.y));
      bisector.mult(dist/sinA);
    }
    offset[i] = PVector.add(crv[i], bisector);
  }
  //do first and last
  PVector dir = PVector.sub(crv[1],crv[0]);
  dir.normalize();
  dir.mult(dist);
  dir.set(-dir.y,dir.x,0);
  offset[0] = PVector.add(crv[0],dir);
  
  dir = PVector.sub(crv[crv.length-1],crv[crv.length-2]);
  dir.normalize();
  dir.mult(dist);
  dir.set(-dir.y,dir.x,0);
  offset[crv.length-1] = PVector.add(crv[crv.length-1],dir);
  return offset;
}