Class: LayoutItem::GroupItem

Inherits:
LayoutItem
  • Object
show all
Defined in:
app/models/layout_item/group_item.rb

Overview

A set of LayoutItems in a Layout, e.g. images selected together, so that they can be labelled and moved as one. Members are its children (their parent_id). A GroupItem references no object.

Intent: groups are translation only.

  • x, y: an offset applied to all members (members' x, y are relative to it, see CompositionItem's Coordinate system). nil is 0, so a group created at nil/0 leaves its members exactly where they were. Moving a set is one update of the group's x, y.
  • text: optional label.

Limitations (deliberate, may be revisited):

  • No zoom, rotation_z, z, width, height, crop, opacity or visibility on a group. Rotating or scaling a set is done on the members, by the client. Members stack by their own z, interleaved with everything else.
  • No stored bounds: a group's extent is derived from its members, by the client (e.g. for a selection outline), so it can never go stale.
  • Groups are the only parents allowed in a Layout (see LayoutItem), so a renderer only ever sums offsets: it can paint all leaf items in one layer sorted by z, and treat groups as logical (offset + membership).
  • An item belongs to at most one group (parent_id). For overlapping, many-to-many sets use Tags on the depicted objects.

Destroying a group ungroups: its members are kept where they appear (see #release_members). To remove a group and its members, destroy the members too.

Instance Method Summary collapse

Instance Method Details

#release_members ⇒ Object (protected)

Keeps the members where they appear: each moves to the group's parent, with the group's offset added to its x, y. Members are appended to the parent's list in their order.



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# File 'app/models/layout_item/group_item.rb', line 45

def release_members
  children.order(:position).each do |m|
    m.update!(
      parent_id:,
      x: (m.x || 0) + (x || 0),
      y: (m.y || 0) + (y || 0)
    )
  end
  # The cascade must not reuse the loaded (now released) members.
  children.reset
end