Connection Pins

2D Graphics > Grapher > Features of the Grapher Package > Grapher Links > Connection Pins

Connection Pins

Connection pins allow you to control the exact location of link end points on grapher nodes. When a link is attached to a connection pin, the connecting point stays the same, regardless of the relative position of its start and end nodes.

The following items are described in this section:

Connection Pin Management Class

An All-Purpose IlvGrapherPin Subclass

Extending the IlvGrapherPin Class

Connection Pin Management Class

The IlvGrapherPin abstract class is designed to handle a collection of connection pins. Its first purpose is to maintain the association between links and pins. To do so, pins are referenced by indexes. You can connect a link to a given connection pin with the IlvGrapherPin::setPinIndex method:

IlvLinkImage* link = …;

//== Recover the IlvGrapherPin instance associated with the starting node

IlvGrapherPin* pin = IlvGrapherPin::Get(link->getFrom());

//== Connect the link to the pin whose index is 0

pin->setPinIndex(link,0,IlTrue);

Likewise, you can recover the index of the connection pin to which a link is attached, by using the IlvGrapherPin::getPinIndex method.

The second purpose of the IlvGrapherPin class is to provide an interface to query the coordinates of the connecting points available for a given node. Each concrete subclass must provide an implementation for the getCardinal and getLocation methods:

virtual IlUInt getCardinal(const IlvGraphic* node,

const IlvTransformer* t) const;

This method returns the number of connection pins handled by the instance for the specified node node when displayed with the transformer t.

virtual IlBoolean getLocation(IlUInt pinIndex,

const IlvGraphic* node,

const IlvTransformer* t,

IlvPoint& where) const;

This method returns, in the where parameter, the coordinates of the connection pin specified by the index pinIndex on the node node, when displayed with the transformer t.

Other methods of this interface (getClosest, IlvGrapherPin::getLinkLocation, and so on) have a default implementation that can be overloaded. For example, the getClosest method considers all available connection pins and uses the getLocation method. You can change this method to:

provide a faster implementation (getLocation may contain computations that can be done only once in getClosest),

return the first unused pin instead of the closest one in terms of distance.

An All-Purpose IlvGrapherPin Subclass

The IlvGenericPin class is a predefined concrete subclass of IlvGrapherPin that makes it possible to dynamically define the connection pins on a node. New connection pins are specified by their desired location on the node when this node is displayed through a given transformer. Once this position is stored, the IlvGenericPin class will use the shape of the object to accurately locate the connecting point regardless of the applied transformer.

Here is an example of how to use this class to add connection pins on the four corners of a node bounding box:

IlvGraphic* node = ...;

//== Create an empty instance of IlvGenericPin

IlvGenericPin* pin = new IlvGenericPin();

//== Add the four connecting points

IlvRect bbox;

node->boundingBox(bbox,0);

pin->addPin(node,IlvPoint(bbox.x(),bbox.y()),0);

pin->addPin(node,IlvPoint(bbox.x()+bbox.w()-1,bbox.y()),0);

pin->addPin(node,IlvPoint(bbox.x()+bbox.w()-1,bbox.y()+bbox.h()-1),0);

pin->addPin(node,IlvPoint(bbox.x(),bbox.y()+bbox.h()-1),0);

//== Attach the IlvGenericPin instance to the node

pin->set(node);

Note: The points in this example are given in the object coordinate system when no transformer is applied.

Extending the IlvGrapherPin Class

An example of a concrete IlvGrapherPin subclass that handles a single connection pin located at the center of a node bounding box is presented here. This class, called CenterPin, is declared as follows:

#include <ilviews/grapher/pin.h>

class CenterPin

: public IlvGrapherPin

{

public:

CenterPin() {}

virtual IlUInt getCardinal(const IlvGraphic*,

const IlvTransformer*) const;

virtual IlBoolean getLocation(IlUInt,

const IlvGraphic*,

const IlvTransformer* t,

IlvPoint&) const;

DeclarePropertyInfoRO();

DeclarePropertyIOConstructors(CenterPin);

};

The constructor of the CenterPin class does nothing since this class does not store any information. The DeclarePropertyInfoRO and DeclarePropertyIOConstructors macros are used to make the CenterPin class persistent. Only the getCardinal and getLocation methods are overloaded since the implementation of the other IlvGrapherPin methods does not need to be changed. The source file for the CenterPin class defines the following methods:

#include <centerpin.h>

// -------------------------------------------------------------------------

// - IO Constructors

CenterPin::CenterPin(IlvInputFile& input, IlvSymbol* s)

: IlvGrapherPin(input, s) {}

CenterPin::CenterPin(const CenterPin& src)

: IlvGrapherPin(src) {}

// -------------------------------------------------------------------------

IlUInt

CenterPin::getCardinal(const IlvGraphic*,

const IlvTransformer*) const

{

return 1;

}

// -------------------------------------------------------------------------

IlBoolean

CenterPin::getLocation(IlUInt,

const IlvGraphic* node,

const IlvTransformer* t,

IlvPoint& where) const

{

IlvRect bbox;

node->boundingBox(bbox, t);

where.move(bbox.centerx(), bbox.centery());

return IlTrue;

}

// -------------------------------------------------------------------------

// - Macros to register the class and make it persistent

IlvPredefinedPropertyIOMembers(CenterPin)

IlvRegisterPropertyClass(CenterPin, IlvGrapherPin);

The implementation of the getCardinal method is straightforward and returns 1 for any node and transformer. The getLocation method simply queries the transformed bounding box of the node and returns its center. (The index of the connection pin is not used since this class defines only one connection pin.) The declaration of the CenterPin class is provided in the file <ILVHOME>/samples/grapher/include/centerpin.h. Its implementation can be found in the file <ILVHOME>/samples/grapher/src/centerpin.cpp.

Version 6.2.1