Tk_CanvasTextInfo(3) Tk (4.0) Tk_CanvasTextInfo(3)
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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 manage
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_CanvasGetTextInfo 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
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Tk_CanvasTextInfo(3) Tk (4.0) Tk_CanvasTextInfo(3)
characters in selItemPtr, as returned by the indexProc for
that item. anchorItemPtr points to the item that currently
has the selection anchor; this is not 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 insertBorderWidth 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
insertion 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
manager calls Tk_CanvasGetTextInfo once when an item is
created 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
selBorder 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 successive
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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