Developer's Guide: The class Selectable

The class Protocols | The Document and Graphics Classes | The class Primitive

## The class `Selectable`

The class `Selectable` defines the interface for objects that can be selected with the mouse. This includes tests for whether the object is hit by a mouse click and methods for the handles.

### The Selection Mechanism

Yet to be written...

### Methods

A `Selectable` object has these methods:

`Hit(p, rect, device [, clip])`

  Return true if clicking at p (a point object) should select the object. The parameter device is a graphics device that can convert points between document coordinates and window coordinates. p is always given in document coordinates.

  rect is a rect object in doc-coordinates that describes a small area around p (a few pixels wide). A point of the object should be considered `hit' if it lies inside this rectangle.

  The device parameter is necessary, because clicking on a special point should have some tolerance, so that `missing' by a few pixels still selects that point. Unfortunately, pixels are screen coordinates and the object's coordinates are document coordinates, so conversion between the two is sometimes necessary. device has some methods for this and also for testing if certain primitives are hit. Currently device is an instance of `HitTestDevice`

  The optional parameter clip is only provided if the object is used as a clip mask. If it is provided its value is 1. Objects that can be used as clip masks (their `is_clip` flag is true) should test whether p is inside of the object regardless of whether they are filled or not. Objects that cannot be used as clip masks don't need to accept it.

`SelectSubobject(p, rect, device[, path])`

  When the parent decides that one of its children (or one of the child's descendants) is to be selected (this is determined using the children's bounding rects and their `Hit` methods), it calls this method to ask the child for details.

  Normally, self should be returned (this is also the default behavior). To select a subobject, return selection info relative to self as a single tuple of selection info. (see selinfo.py)

  Compound objects like groups and layers override this method to let the user select their children.

  As in `Hit`, p and rect describe a point and a small tolerance rectangle around it, and device is a `HitTestDevice`. The optional argument path is useful only for compound objects but has to be accepted by all graphics objects.

The class Protocols | The Document and Graphics Classes | The class Primitive