getFollowerOffset abstract method
Returns the offset at which to position the follower element in relation
to the top left of the targetSize.
The followerSize is the final size of the follower element after layout
For example, if it is used in portals, it is based on the follower
constraints determined by Anchor.getFollowerConstraints.
The targetSize represents the bounds of the element which the follower
element should be anchored to. If it is used in portals, this must be
the same value that is passed to Anchor.getFollowerConstraints.
The theaterRect represents the bounds of the full available space to
place the follower element in. Note that this is also relative to the top
left of the targetSize.
This means that every offset going into or coming out of this function is
relative to the top-left corner of the target.
Example
In this example, our follower element has a size of Size(30, 30) and
should be anchored to the bottom right of the target.
If we assume the full available space starts at absolute (0, 0) and
spans to absolute (100, 100) and the target rect starts at absolute
(40, 40) and spans to absolute (60, 60), the passed values will be:
Rect.fromLTWH(0, 0, 20, 20)for thetargetSize.Rect.fromLTWH(-40, -40, 100, 100)for thetheaterRect.Size(30, 30)for thefollowerSize.Offset(20, 20)as the return value.
Implementation
Offset getFollowerOffset({
required Size followerSize,
required Size targetSize,
required Rect theaterRect,
});