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

class move_outline_gesture {#class-move_outline_gesture}

A move_outline gesture is very similar to a move_gesture object, except that it drags a dotted box instead of the object itself and only moves the object when the user releases the button.

The move-outline gesture is to be preferred if the graphical has constraints or connections because the move_gesture will force recomputing these constraints and connections on each drag-event, while the move_outline_gesture will do so only when the user releases the button.

Bugs:

The outline is a box that is actually (temporary) displayed on the same device as the graphical to be moved. The current implementation of PCE's repaint algorithm requires significant repaint operations to be performed each time the outline-box is moved. A dedicated implementation of the outline (using XOR'ing or copying) would improve efficiency.

move_outline_gesture<-outline: box Box used to paint the outline moved. The attributes box ->texture, box ->pen, etc, may be changed.

move_outline_gesture->drag: event Delegates the event to the <-outline using event ->post, thus moving the <-outline rather than the object.
move_outline_gesture->initiate: event Displays the <-outline on the same device as the graphical moved. Than uses event ->post to initiate the normal move_gesture object associated with the <-outline.
move_outline_gesture->terminate: event First invoke ->drag. Next it invokes ->set with the x, y, w and h of the area of the <-outline to event <-receiver. Finally it invokes graphical ->device: @nil to the <-outline to remove it from the device.