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

class region {#class-region}

A region object defines a sub-area of an area, expressed using function objects to denote the X, Y, W and H of the sub-area in terms of the dimensions of the main area.

Regions are used by handler objects to denote the handler should only respond when an event object occurred in some sub-area of a graphical. As handler objects have become old-fashioned since the introduction of class gesture this class too is seldomly used.

For example, the region

region(x, y, w/10, h/10)

Denotes a region with the same origin as the area it is related to, extending to 10% in both directions.

@see class expression @see class area @see class handler

region<->height: expression Expresses the named dimension of the region in terms of the dimensions of the area (see ->inside). The expression is passed the variables x, y, w and h denoting the dimensions of the area. See also class binary_expression.
region<->width: expression Inherits description from: region-height
region<->x: expression Inherits description from: region-height
region<->y: expression Inherits description from: region-height

region<-area_width: area -> int
region<-area_x: area -> int
region<-area_y: area -> int
region<-area_height: area -> int Dimension of the described region for the specified area. Example:
```
?- get(region(x+w/2, y+h/2, w/2, h/2), area_height,
       area(100, 100, 200, 200), H),

H = 100
```