code: public void set(double x1, double y1, double x2, double y2) {
          this.MODE = LINES;
          this.x1 = x1;
          this.y1 = y1;
          this.x2 = x2;
          this.y2 = y2;
  
          calcG();
          dx[0] = x1 - x;
          dx[1] = x2 - x;
          dy[0] = y1 - y;
          dy[1] = y2 - y;
          dz[0] = z1 - 0;
          dz[1] = z2 - 0;
          if (dashed) calcDashedLine();
      }
docs: Sets the coordinates for the first and second point.
  
  @param x1 The x-coordinates for the first point.
  @param y1 The y-coordinates for the first point.
  @param x2 The x-coordinates for the second point.
  @param y2 The y-coordinates for the second point.