eric6.Graphics.AssociationItem

Module implementing a graphics item for an association between two items.

Global Attributes

Classes

Functions

AssociationItem

Class implementing a graphics item for an association between two items.

The association is drawn as an arrow starting at the first items and ending at the second.

Derived from

Class Attributes

Class Methods

Methods

Static Methods

AssociationItem.parseAssociationItemDataString (class method)

Class method to parse the given persistence data.

data

persisted data to be parsed (string)

Returns:

tuple with the IDs of the source and destination items, the association type and a flag indicating to associate from top to bottom (integer, integer, integer, boolean)

AssociationItem (Constructor)

Constructor

itemA

first widget of the association

itemB

second widget of the association

assocType

type of the association. This must be one of

• Normal (default)
• Generalisation
• Imports

topToBottom (bool)

flag indicating to draw the association from item A top to item B bottom

colors (tuple of (QColor, QColor))

tuple containing the foreground and background colors

parent (QGraphicsItem)

reference to the parent object

AssociationItem.__calculateEndingPoints_center

Private method to calculate the ending points of the association item.

The ending points are calculated from the centers of the two associated items.

AssociationItem.__calculateEndingPoints_rectangle

Private method to calculate the ending points of the association item.

The ending points are calculated by the following method.

For each item the diagram is divided in four Regions by its diagonals as indicated below

            +------------------------------+
            |        \  Region 2  /        |
            |         \          /         |
            |          |--------|          |
            |          | \    / |          |
            |          |  \  /  |          |
            |          |   \/   |          |
            | Region 1 |   /\   | Region 3 |
            |          |  /  \  |          |
            |          | /    \ |          |
            |          |--------|          |
            |         /          \         |
            |        /  Region 4  \        |
            +------------------------------+
        

Each diagonal is defined by two corners of the bounding rectangle.

To calculate the start point we have to find out in which region (defined by itemA's diagonals) is itemB's TopLeft corner (lets call it region M). After that the start point will be the middle point of rectangle's side contained in region M.

To calculate the end point we repeat the above but in the opposite direction (from itemB to itemA)

AssociationItem.__calculateEndingPoints_topToBottom

Private method to calculate the ending points of the association item.

The ending points are calculated from the top center of the lower item to the bottom center of the upper item.

AssociationItem.__findIntersection

Private method to calculate the intersection point of two lines.

The first line is determined by the points p1 and p2, the second line by p3 and p4. If the intersection point is not contained in the segment p1p2, then it returns (-1.0, -1.0).

For the function's internal calculations remember:
QT coordinates start with the point (0,0) as the topleft corner and x-values increase from left to right and y-values increase from top to bottom; it means the visible area is quadrant I in the regular XY coordinate system

            Quadrant II     |   Quadrant I
           -----------------|-----------------
            Quadrant III    |   Quadrant IV
        

In order for the linear function calculations to work in this method we must switch x and y values (x values become y values and viceversa)

p1

first point of first line (QPointF)

p2

second point of first line (QPointF)

p3

first point of second line (QPointF)

p4

second point of second line (QPointF)

Returns:

the intersection point (QPointF)

AssociationItem.__findPointRegion

Private method to find out, which region of rectangle rect contains the point (PosX, PosY) and returns the region number.

rect

rectangle to calculate the region for (QRectF)

posX

x position of point (float)

posY

y position of point (float)

Returns:

the calculated region number
West = Region 1
North = Region 2
East = Region 3
South = Region 4
NorthWest = On diagonal 2 between Region 1 and 2
NorthEast = On diagonal 1 between Region 2 and 3
SouthEast = On diagonal 2 between Region 3 and 4
SouthWest = On diagonal 1 between Region4 and 1
Center = On diagonal 1 and On diagonal 2 (the center)

AssociationItem.__findRectIntersectionPoint

Private method to find the intersetion point of a line with a rectangle.

item

item to check against

p1

first point of the line (QPointF)

p2

second point of the line (QPointF)

Returns:

the intersection point (QPointF)

AssociationItem.__mapRectFromItem

Private method to map item's rectangle to this item's coordinate system.

item

reference to the item to be mapped (QGraphicsRectItem)

Returns:

item's rectangle in local coordinates (QRectF)

AssociationItem.__updateEndPoint

Private method to update an endpoint.

region

the region for the endpoint (integer)

isWidgetA

flag indicating update for itemA is done (boolean)

AssociationItem.buildAssociationItemDataString

Public method to build a string to persist the specific item data.

This string should be built like "attribute=value" with pairs separated by ", ". value must not contain ", " or newlines.

Returns:

persistence data (string)

AssociationItem.unassociate

Public method to unassociate from the widgets.

AssociationItem.widgetMoved

Public method to recalculate the association after a widget was moved.