Enclosure Polygon

Rather than a bounding box rectangle, this computes a transformed element's enclosure in screen points. The enclosure is a polygon that responds to the element's transforms.
All elements are transformed.
The blue rect and orange circle are contained in a group.

Each polygon enclosure shown is at screen points.

Path Enclosure:

Group Enclosure:

Ellipse Enclosure:

Polygon Enclosure:

SVG Source: