nearestCornerInset
The corner and margin that bring an image overlay's own corner to this point.
The inverse of what ImageOverlay.placedOn does with ImageOverlay.corner and ImageOverlay.margin, for a caller holding a position a drag produced. The corner is the quadrant of the frame the point falls in, and the margin is read back off the two insets from it. One margin answers for both axes, so a point off the diagonal the forward arithmetic reaches takes the margin midway between the two the insets imply.
Only the frame's proportions are read, so a measurement in view pixels answers the same as one in output pixels. A point far enough past the middle that the forward arithmetic would hold the margin at half the frame does not come back as the margin that produced it.
Return
The corner the point sits nearest and the margin that reaches it.
Parameters
The frame the point is measured on, in pixels.