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

class joint {#class-joint}

Class joint is a super-class for all line-like graphical classes that may have arrows at either or both ends of the line. Currently it has the following subclasses:

class line Straight line-segment
class arc Part of an ellipse (or circle).
class path Line through a number of control-points. May be smooth (interpolated) or a series of straight line-segments.
class bezier_curve Smooth curve leaving <-start in the direction of a control-point to <-end arriving from the direction of a contol-point.

Class joint defines all methods that deal with attaching and deleting arrows at the start or end of the line. Despite the name, the ->arrows related to a joint need not be instances of class arrow. Instead, they may be instances of any subclass of class graphical, provided the class inplements the ->points method compliant to arrow->points. This allows the definition of new arrow like objects and attaching them to the tips of line-like objects

See ->arrows, ->first_arrow and ->second_arrow. See also class arrow.

@see class arrow

joint<-first_arrow: graphical* Arrow object at the start-point of the joint. If @nil, no arrow is displayed. Default (simple) arrows are normally attached using ->arrows.

Any graphical implementing ->points compliant to arrow->points can be used as an arrow head. If the joint is changed, it's ->compute method will send ->points to the arrow object and recompute the bounding box of the joint. Similar, ->redraw will draw invoke the ->redraw method of the arrow(s).
joint<-second_arrow: graphical* Arrow object at the end-point of the joint. If @nil, no arrow is displayed.

joint->arrows: arrows={none,first,second,both} Inherits description from: joint<-arrows
joint->initialise: x=[int], y=[int], width=[int], height=[int], arrows=[{none,first,second,both}] For an application programmer it is not useful to make instances of class joint directly. See line ->initialise, arc ->initialise and path ->initialise.

joint<-arrows: -> arrows={none,first,second,both} The <->arrows method provides a simple interface to ->first_arrow and ->second_arrow. If it attaches arrows the new arrow is created using <-default_arrow.
joint<-default_arrow: -> graphical Create a default arrow (new(arrow)), see arrow->initialise. This method is called by ->arrows. Intended to be redefined for making lines with different arrow styles.