Tk_CanvasTextInfo(3) Tk Library Procedures 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 does not 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 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

Tk 4.0 Tk_CanvasTextInfo(3)