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>Organization of items</A
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> Items in the canvas are organized in a tree hierarchy. Items
can be groups (nodes in the tree), or terminal items (leaves in
the tree). Groups can contain any number of children, which can
be terminal items or other groups. Thus, items can be nested to
an arbitrary depth inside a canvas.
</P
><P
> A canvas has a single root group. For simple drawings, it is
likely that you will want to put all your items directly inside
this group. For more complex drawings, it may be convenient to
use a hierarchical structure of nested canvas groups.
</P
><P
> For example, consider a circuit editor. You could define
groups that contain the items that are necessary to draw a
certain type of logic gate. Then you could define groups for
different components. A group representing an adder would
contain several logic gates and some wires. You would then
group some adders with other components to form a more complex
circuit. This makes it convenient to handle whole hierarchies
as single entities, for when you want to move all the items
that define a chain of adders, for example.
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> The items you put inside groups are stacked on top of each
other, and items nearer the top of the stack obscure the items
below them. When an item is created, it is put on top of all
the items in its parent group.
</P
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> The canvas provides several functions to let you change the
stacking order of items inside groups. You can move items
to the top or bottom of their parent group, and raise or
lower them by an arbitrary number of positions.
</P
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> The canvas does <I
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behavior for items. You can define the behavior of items by
explicitly operating on them (change the color if item Foo
when the user selects a menu item), or by defining actions
that should take place when items receive events (let the
user drag items with the mouse).
</P
><P
> The rationale behind this is that the canvas should be as
general-purpose as possible. If it had predefined behavior
for items, it may not be suitable to all kinds of
applications — a program for drawing schematic
diagrams may benefit from having dragging functionality
predefined in the canvas, but this would not be very useful
(or even desirable) for a calendar display program.
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distrib
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Mandriva
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2010.0
>
i586
>
media
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contrib-release
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by-pkgid
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1bbf51ece72e40a5f40ad48678e7c5a5
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files
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246
