layout_manager.md
In rswipl: Embed 'SWI'-'Prolog'

class layout_manager {#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 class device @see class layout_interface @see class table

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 ->compute is pending; the device polls this slot before the next redraw.

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 <-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.