code: public static void translateM(
              float[] m, int mOffset,
              float x, float y, float z) {
          for (int i=0 ; i<4 ; i++) {
              int mi = mOffset + i;
              m[12 + mi] += m[mi] * x + m[4 + mi] * y + m[8 + mi] * z;
          }
      }
docs: Translates matrix m by x, y, and z in place.
  @param m matrix
  @param mOffset index into m where the matrix starts
  @param x translation factor x
  @param y translation factor y
  @param z translation factor z