Developer's Guide: The class Protocols

The class HierarchyNode | The Document and Graphics Classes | The class Selectable

## The class `Protocols`

While sharing a common interface, the various types of graphics objects provide a variety of additional capabilities and interfaces. The class `Protocols` defines some flags that indicate the presence of certain standard extensions. These flags are boolean class variables with names of the form ``is_`*' or ``has_`*'. By default all of these flags are false. Derived classes are expected to set the appropriate flags.

The standard flags are:

`has_properties`

  True, iff object can have properties. If true, the object must implement the methods `AddStyle`, `Properties`, `SetProperties`, `ObjectChanged` and `ObjectRemoved`.

  The class `Primitive` provides this interface.

`has_fill`

  True, iff object can have fill properties. If true, `has_properties` must also be true. In addition, the object must implement the method `Filled` and the method `SetProperties` must accept the fill properties.

  The class `Primitive` provides this interface.

`has_line`

  True, iff object can have line properties. If true, `has_properties` must also be true. In addition, the object must implement the method `LineWidth` and the method `SetProperties` must accept the line properties.

  The class `Primitive` provides this interface.

`has_font`

  True, iff object can have a font. If true, `has_properties` must also be true. In addition, the method `SetProperties` must accept the font properties.

`is_Bezier`
`is_Rectangle`
`is_Ellipse`
`is_Text`
`is_Image`
`is_Eps`

  Indicate the type of object.

`is_Compound`

  True, iff the object is a compound object.

`is_Group`

  True, iff the object is a group. A group is a compound object. A group object can be ungrouped, that is, the user can issue a command that replaces the group with its children, which become direct children of the group's parent. To this end, a group must provide the method `Ungroup`. (see the document method `UngroupSelected`)

`is_Blend`

  True, iff the object is a blend group.

`is_curve`

  True, iff the object can be converted to a `PolyBezier` object. If true, the object must implement the methods `AsBezier` and `Paths`.

  Skencil treats the PolyBezier as a kind of `common denominator' for blending. For instance, if you try to blend a rectangle and an ellipse, both are converted to beziers and the beziers are blended.

`is_clip`

  True, iff the object may be used as a clip mask. If true, the methods `Hit` and `DrawShape` must accept an additional boolean parameter `clip` indicating whether the object is used as a clip mask.

The class HierarchyNode | The Document and Graphics Classes | The class Selectable