How to use

atan2

method

in

processing.core.PApplet

/**
 * Return the x,y positions of a 3D location projected onto a given
 * reference. The Z axis is the angle (in radians) given by the rotation of
 * the positionToFind.
 *
 * @param positionToFind
 * @param reference
 * @return
 */
public PVector projectPositionTo2D(PMatrix3D positionToFind,
    PMatrix3D reference,
    float referenceHeight) {
  PMatrix3D referenceInv = reference.get();
  referenceInv.invert();
  PMatrix3D relative = positionToFind.get();
  relative.preApply(referenceInv);
  PMatrix3D positionToFind2 = positionToFind.get();
  positionToFind2.translate(100, 0, 0);
  PMatrix3D relative2 = positionToFind2.get();
  relative2.preApply(referenceInv);
  PVector out = new PVector();
  float x = relative.m03 - relative2.m03;
  float y = relative.m13 - relative2.m13;
  out.z = PApplet.atan2(x, y);
  out.x = relative.m03;
  out.y = referenceHeight - relative.m13;
  return out;
}

/**
 * Return the x,y positions of a 3D location projected onto a given
 * reference. The Z axis is the angle (in radians) given by the rotation of
 * the positionToFind.
 *
 * @param positionToFind
 * @param reference
 * @return
 */
public PVector projectPositionTo(PMatrix3D positionToFind,
    PaperScreen reference) {
  PMatrix3D referenceInv = reference.getLocation().get();
  referenceInv.invert();
  PMatrix3D relative = positionToFind.get();
  relative.preApply(referenceInv);
  PMatrix3D positionToFind2 = positionToFind.get();
  positionToFind2.translate(100, 0, 0);
  PMatrix3D relative2 = positionToFind2.get();
  relative2.preApply(referenceInv);
  PVector out = new PVector();
  float x = relative.m03 - relative2.m03;
  float y = relative.m13 - relative2.m13;
  out.z = PApplet.atan2(x, y);
  out.x = relative.m03;
  out.y = reference.drawingSize.y - relative.m13;
  return out;
}

  public void drawOnTable() {
    if (!isDrawingOnDisplay) {
      return;
    }

//        PMatrix3D location = this.getLocation().get();
//        PMatrix3D t = tableInv.get();
//        t.apply(location);
//        PVector tableRelativePos = new PVector(t.m03, t.m13, t.m23);
    PVector p2 = getRelativePos(new PVector(20, 20, 0));
    PVector tableRelativePos = getRelativePos(new PVector(0, 0, 0));

    float r = PApplet.atan2(p2.y - tableRelativePos.y, p2.x - tableRelativePos.x);

    PMatrix3D locationInv = this.getLocation().get();
    locationInv.invert();
    currentGraphics.scale(1, -1, 1);
    currentGraphics.translate(0, -getSize().y, 0);
    currentGraphics.applyMatrix(locationInv);
    currentGraphics.applyMatrix(table);
    currentGraphics.translate(tableRelativePos.x, tableRelativePos.y);
    currentGraphics.rotate(r);
    currentGraphics.scale(1, -1, 1);
  }

phi1 = PApplet.atan2(sy, sx);
phiDelta = (((PApplet.atan2(ty, tx) - phi1) % TWO_PI) + TWO_PI) % TWO_PI;
if (!fs) phiDelta -= TWO_PI;