Tk_CanvasTextInfo − additional information for managing text items in canvases


#include <tk.h>

Tk_CanvasTextInfo *


Tk_Canvas canvas (in)

A token that identifies a particular canvas widget.



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.


canvas, focus, insertion cursor, selection, selection anchor, text


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