In my photo editor project the images sit alongside each other as per the top of this diagram.
When you scale up the images (zoom) one obviously "underlaps" the other.
Blue has dragging - red is pinned to Blue
Dragging works fine until you get to the edge where there is no overlap. So basically, the images are draggable up to a point.
I have so far overcome this by making the Blue image larger so that it totally overlaps the Red one and is therefore draggable across all it's surface.
However, is there a better way to do this?