                  const bl = new CubicBezierPatch(), br = new CubicBezierPatch();
                    patch.subdivide(tl, bl, tr, br); 
                    this._renderFilledSubdivisionPathsRecursive(ctx, tl, currentLevel + 1, targetMaxLevel, quad_x * 2,     quad_y * 2);
                    this._renderFilledSubdivisionPathsRecursive(ctx, tr, currentLevel + 1, targetMaxLevel, quad_x * 2 + 1, quad_y * 2);
                    this._renderFilledSubdivisionPathsRecursive(ctx, bl, currentLevel + 1, targetMaxLeve