BLOP -- GRaphical OBjects (grobs)

GRaphical OBjects (grobs)

The name 'grob' originates from LilyPond, a music typesetter, and it stands for GRaphical OBject. Grob is the base class for all objects which you place in your plot (except graph). Grob defines a few common properties:

Objects are placed into the object hierarchy, as explained before. This means, that all objects are placed into containers, (except the topmost container, the canvas). Grob defines the autodel flag. If this flag is set to true, the grob will be automatically deleted when his parent container is deleted or cleared. This serves the purpose of garbage collection, and grobs created by blop's utility function (using operator new) have this flag automatically set to true.
Grob defines the following member functions:

off()
The object is switced off, it will not appear on the terminal, when its parent canvas is printed. Its dimensions are not specialized (these are details, you can skip them), using them will not be valid

invisible()
The object will be invisible (it will not appear on the terminal), but its dimensions will be calculated and specialized, so you can aligh other objects to this just as if it would be there on your plot. This and the previous off() function can be used for example to hide certain parts of your plot at special conditions

on()
The object is switched on, it will appear on the terminal. All objects are by default switched on, you will need this function only if you switched them off, or made them invisible before.

The 'container *parent()' member function returns the parent of this object (the container in which it is placed, or NULL if it is not placed into any container)

The print_hierarchy() member function prints the object-hierarchy onto your standard error output beginning with this object. For example if you want to check what objects are stored in your current pad, say: pad::current()->print_hierarchy();

etc, etc, etc.

Objects may need to be prepared for drawing. For example they can hold only some preliminary info about themselves, and they calculate their final layout only before being printed. Or, as it was explained before, lengths need to be specialized before they can be used in any printing process. The coordinates of grobs have to be registered in order that they will be specialized (I would wonder if this were clear... let me have a chance later to explain it better :-). The member function prepare_for_draw()(which is pure virtual) usually does this, and this member function is overridden in derived classes. The user never has to call this function.

Source files:
   grob.h
   grob.cc