surfacesplat.java

//Simple, bad surface splatting.  Actually difficult
//Does not check for degenerate cases
for(int i=0;i<points.size();++i) {
  PVector pt = (PVector) points.get(i);
  PVector normal = (PVector) normals.get(i);
  //draw a circle oriented towards normal at pt
  //get rotation angles
  float theta = atan2(normal.y,normal.x); //angle around z axis
  float psi = atan2(sqrt(normal.x*normal.x+normal.y*normal.y),normal.z); //angle from z axis
  //get local axes
  PVector perp1 = normal.cross(new PVector(normal.x,normal.y,0));
  perp1.normalize();
  PVector perp2 = normal.cross(perp1);
  perp2.normalize();
  //get coordinates of pt in local axis by projecting
  float localZ = normal.dot(pt);
  float localY = perp1.dot(pt);
  float localX = -perp2.dot(pt);
  pushMatrix();
  rotateZ(theta);
  rotateY(psi);
  translate(localX,localY,localZ);
  ellipse(0,0,diameter,diameter);
  popMatrix();
}