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Creating Display Items
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Display Items
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Advantages of Display
Display Items and Display Styles
The appearance of a display item is controlled by a set of
attributes. For example, the
text
attribute controls the text
string displayed on the item and the
font
attribute specifies
what font should be used.
Usually, each of the attributes falls into one of two categroies:
``
individual
'' or ``
collective
''. For example, each of
the items inside a TixTList widget may display a different text
string; therefore we call the text string an
individual
attribute
. However, in most cases, the items share the same color,
font and spacing and we call these
collective attributes
.
One question concerns where we keep the collective attribute for the
display items. Certainly, we can keep a
font
attribute for each
item, but this is not really an efficient solution. In fact, if all the
items have the same font, we would be keeping a duplicated copy of the
same font for each of the items we create. Since a host widget may have
many thousands of items, keeping thousands of dupilcated copys of the
same font, or any other collective attributes, would be very wasteful.
To avoid the unnecessary duplication of resources, Tix stores the
collective attributes in special objects called
display styles
. The
relationship between display items and their styles is depicted in figure
3-4. Each item holds its own copy of the individual
attributes, such as
text
. However, the collective attributes are
stored in the style objects. Each item has a special
style
attribute that tells it which style it should use. In figure 3-4
, since items
a
and
b
are assigned the same
style, therefore, they share the same font and color. Item
c
is
assigned a different style, thus, it uses a different font than
a
and
b
.
http://tix.sourceforge.net
http://tix.sourceforge.net
