code: public void set(double x1, double y1, double x2, double y2, double x3, double y3, double x4, double y4) {
          this.x1 = x1;
          this.y1 = y1;
          this.x2 = x2;
          this.y2 = y2;
          this.x3 = x3;
          this.y3 = y3;
          this.x4 = x4;
          this.y4 = y4;
          calcG();
      }
docs: Sets x,y-coordinate of corners.
  
  @param x1 The x-coordinate of the first corner.
  @param y1 The y-coordinate of the first corner.
  @param x2 The x-coordinate of the second corner.
  @param y2 The y-coordinate of the second corner.
  @param x3 The x-coordinate of the third corner.
  @param y3 The y-coordinate of the third corner.
  @param x4 The x-coordinate of the fourth corner.
  @param y4 The y-coordinate of the fourth corner.