Life as Clay

Archive for February 2013

Processing class for finding normal vectors

leave a comment »

Processing uses the PVector class to store vector data. The .normalize() method will normalize any PVector to a unit vector. What I needed to do was to find the normal of a vector — a vector perpendicular to the original vector. This is easy enough to do with some simple math. However, I wanted to encapsulate the logic into a class so that I could store multiple perpendicular vectors (to an original vector) and different locations along the original vector, and at different magnitudes. That is what this class does:


class PerpVectorPack {
  // Store the original data
  PVector originalVector;

  // Keep track of values used to calculate points
  ArrayList<Float>   percentOfOriginalVector;
  ArrayList<Float>   magnitudeOfPerpendicularVector;
  ArrayList<Boolean> onRightSide;

  // Storage of calculated perpendicular line points
  ArrayList pointsOnLine;
  ArrayList perpVectorPoints;

  // Constructors
  PerpVectorPack(PVector origVector) {
    originalVector = origVector.get();

  PerpVectorPack(PVector origVector, float perpVectDist, float perpVectMag, boolean rightSide) {    
    originalVector = origVector.get();
    addPerpVector(perpVectDist, perpVectMag, rightSide);

  private void initializeLists() {
    pointsOnLine                    = new ArrayList();
    perpVectorPoints                = new ArrayList();

    percentOfOriginalVector         = new ArrayList<Float>();
    magnitudeOfPerpendicularVector  = new ArrayList<Float>();
    onRightSide                     = new ArrayList<Boolean>();

  // Methods
  public void addPerpVector(float perpVectDist, float perpVectMag, boolean rightSide) {

    // Keep track of the values used to create the perpendicular points

    PVector full    = originalVector.get();
    float   fullMag = full.mag();

    // Determine where along the original vector the perpendicular vector should lie (lay?)
    full.mult(perpVectDist * fullMag);

    // Set the first local variable

    // Get the normal of the original full vector and normalize it
    PVector perpVector  = new PVector(-originalVector.y, originalVector.x);

    // Determine if it should be on the right or left side of the original vector
    int dir = 1;
    if (!rightSide) dir = -1;

    // Make it the proper length
    perpVector.mult(fullMag * perpVectMag * dir);

    // Offset it from the origin

    // Set the second local variable

  public PVector ptOnOriginalLine() { 
    return ptOnOriginalLine(0);
  public PVector ptOnOriginalLine(int idx) {
    PVector thePoint = (PVector)pointsOnLine.get(idx);
    return thePoint.get();

  public PVector perpVectorPt() { 
    return perpVectorPt(0);
  public PVector perpVectorPt(int idx) {
    PVector thePoint = (PVector)perpVectorPoints.get(idx);
    return thePoint.get();

Written by Clay

February 21, 2013 at 22:44

Posted in Code, Processing, Resource

Tagged with ,