1.88 class layout_manager

A layout_manager is the object responsible for placing the graphicals on a device. The design mirrors recogniser: part of the device's responsibilities (here, geometry) is delegated to an associated object.

A layout_manager is attached to a device via device->layout_manager. The device asks it to recompute the layout and to paint any background. Conversely, the manager assigns each managed graphical a layout_interface (via graphical->layout_interface) that intercepts geometry changes and propagates them back so the manager knows when to recompute.

Class layout_manager itself is an almost-empty abstract base. The first concrete realisation is table, implementing HTML-3-like tables. See also layout_interface.

See also

- class device
- class layout_interface
- class table

1.88.1 Instance variables

layout_manager <- device: device*

Device on which this manager places graphicals.

layout_manager <- request_compute: any*

Set when the layout has become invalid and a layout_manager->compute is pending; the device polls this slot before the next redraw.

1.88.2 Send methods

layout_manager -> initialise

Initialise an abstract instance. Subclasses normally extend this with their own setup.

layout_manager -> attach:graphical

Attach the manager to a device, taking responsibility for the layout of the device's graphicals.

layout_manager -> detach

Detach from the current device.

layout_manager -> unlink

Called when the manager is destroyed: cleanly detach from layout_manager<-device.

layout_manager -> compute

Virtual method: recompute the layout. Subclasses override.

layout_manager -> compute_bounding_box

Virtual method: compute the union bounding box of the laid-out graphicals. The default implementation fails (no contribution).

layout_manager -> RedrawArea:area

Paint background objects for the indicated area. The default implementation succeeds without drawing.