public class Matrix3x3
{
   // PUBLIC ACCESS METHODS

   public void identity() {
      doIdentity(data);
   }

   public void translate(double dx, double dy) {
      doMakeTranslation(dx, dy, temp);
      doMultiply(data, temp, temp2);              // postMultiply
      copyData(temp2, data);
   }

   public void makeTranslation(double dx, double dy) {
      doMakeTranslation(dx, dy, data);
   }

   public void postMultiply(Matrix3x3 src) {
      doMultiply(data, src.data, temp);
      copyData(temp, data);
   }

   public void preMultiply(Matrix3x3 src) {
      doMultiply(src.data, data, temp);
      copyData(temp, data);
   }

   public void transform(double x, double y, double dst[]) {
      dst[0] = data[0][0] * x + data[0][1] * y + data[0][2];
      dst[1] = data[1][0] * x + data[1][1] * y + data[1][2];
   }


   // INTERNAL WORKHORSE METHODS


   protected double data[][] = new double[3][3];


   protected static void doIdentity(double data[][]) {
      for (int i = 0 ; i < 3 ; i++)
      for (int j = 0 ; j < 3 ; j++)
         data[i][j] = i == j ? 1 : 0;
   }

   protected static void doMakeTranslation(double dx, double dy, double data[][]) {
      doIdentity(data);
      data[0][2] = dx;
      data[1][2] = dy;
   }

   protected static void doMultiply(double a[][], double b[][], double c[][]) {
      for (int i = 0 ; i < 3 ; i++)
      for (int j = 0 ; j < 3 ; j++)
         c[i][j] = a[i][0] * b[0][j] + a[i][1] * b[1][j] + a[i][2] * b[2][j];
   }

   protected static void copyData(double src[][], double dst[][]) {
      for (int i = 0 ; i < 3 ; i++)
      for (int j = 0 ; j < 3 ; j++)
         dst[i][j] = src[i][j];
   }

   private double temp[][] = new double[3][3];
   private double temp2[][] = new double[3][3];
}