NAME
Tk_CanvasTextInfo - additional information for managing
text items in canvases
SYNOPSIS
#include <tk.h>
Tk_CanvasTextInfo *
Tk_CanvasGetTextInfo(canvas)
ARGUMENTS
Tk_Canvas canvas (in) A token that identifies a
particular canvas widget.
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DESCRIPTION
Textual canvas items are somewhat more complicated to man
age than other items, due to things like the selection and
the input focus. Tk_CanvasGetTextInfo may be invoked by a
type manager to obtain additional information needed for
items that display text. The return value from Tk_Canvas
GetTextInfo is a pointer to a structure that is shared
between Tk and all the items that display text. The
structure has the following form:
typedef struct Tk_CanvasTextInfo {
Tk_3DBorder selBorder;
int selBorderWidth;
XColor *selFgColorPtr;
Tk_Item *selItemPtr;
int selectFirst;
int selectLast;
Tk_Item *anchorItemPtr;
int selectAnchor;
Tk_3DBorder insertBorder;
int insertWidth;
int insertBorderWidth;
Tk_Item *focusItemPtr;
int gotFocus;
int cursorOn;
} Tk_CanvasTextInfo;
The selBorder field identifies a Tk_3DBorder that should
be used for drawing the background under selected text.
selBorderWidth gives the width of the raised border around
selected text, in pixels. selFgColorPtr points to an
XColor that describes the foreground color to be used when
drawing selected text. selItemPtr points to the item that
is currently selected, or NULL if there is no item
selected or if the canvas doesn't have the selection.
selectFirst and selectLast give the indices of the first
and last selected characters in selItemPtr, as returned by
the indexProc for that item. anchorItemPtr points to the
necessarily the same as selItemPtr. selectAnchor is an
index that identifies the anchor position within
anchorItemPtr. insertBorder contains a Tk_3DBorder to use
when drawing the insertion cursor; insertWidth gives the
total width of the insertion cursor in pixels, and insert
BorderWidth gives the width of the raised border around
the insertion cursor. focusItemPtr identifies the item
that currently has the input focus, or NULL if there is no
such item. gotFocus is 1 if the canvas widget has the
input focus and 0 otherwise. cursorOn is 1 if the inser
tion cursor should be drawn in focusItemPtr and 0 if it
should not be drawn; this field is toggled on and off by
Tk to make the cursor blink.
The structure returned by Tk_CanvasGetTextInfo is shared
between Tk and the type managers; typically the type man
ager calls Tk_CanvasGetTextInfo once when an item is cre
ated and then saves the pointer in the item's record. Tk
will update information in the Tk_CanvasTextInfo; for
example, a configure widget command might change the sel
Border field, or a select widget command might change the
selectFirst field, or Tk might change cursorOn in order to
make the insertion cursor flash on and off during succes
sive redisplays.
Type managers should treat all of the fields of the
Tk_CanvasTextInfo structure as read-only, except for
selItemPtr, selectFirst, selectLast, and selectAnchor.
Type managers may change selectFirst, selectLast, and
selectAnchor to adjust for insertions and deletions in the
item (but only if the item is the current owner of the
selection or anchor, as determined by selItemPtr or
anchorItemPtr). If all of the selected text in the item
is deleted, the item should set selItemPtr to NULL to
indicate that there is no longer a selection.
KEYWORDS
canvas, focus, insertion cursor, selection, selection
anchor, text
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