Tk_GetCursor (3)
maintain database of cursors
SYNOPSIS
#include <tk.h>
Tk_Cursor
Tk_GetCursor(interp, tkwin, nameId)
Tk_Cursor
Tk_GetCursorFromData(interp, tkwin, source, mask, width, height, xHot, yHot, fg, bg)
char *
Tk_NameOfCursor(display, cursor)
Tk_FreeCursor(display, cursor)
ARGUMENTS
"unsigned long" *pixelPtr
Tcl_Interp *interp in
Interpreter to use for error reporting.
Tk_Window tkwin in
Token for window in which the cursor will be used.
Tk_Uid nameId in
Description of cursor; see below for possible values.
char *source in
Data for cursor bitmap, in standard bitmap format.
char *mask in
Data for mask bitmap, in standard bitmap format.
"int" width in
Width of source and mask.
"int" height in
Height of source and mask.
"int" xHot in
X-location of cursor hot-spot.
"int" yHot in
Y-location of cursor hot-spot.
Tk_Uid fg in
Textual description of foreground color for cursor.
Tk_Uid bg in
Textual description of background color for cursor.
Display *display in
Display for which cursor was allocated.
Tk_Cursor cursor in
Opaque Tk identifier for cursor. If passed toTk_FreeCursor, must
have been returned by some previous call to Tk_GetCursor or
Tk_GetCursorFromData.
DESCRIPTION
These procedures manage a collection of cursors
being used by an application. The procedures allow cursors to be
re-used efficiently, thereby avoiding server overhead, and also
allow cursors to be named with character strings (actually Tk_Uids).
Tk_GetCursor takes as argument a Tk_Uid describing a cursor,
and returns an opaque Tk identifier for a cursor corresponding to the
description.
It re-uses an existing cursor if possible and
creates a new one otherwise. NameId must be a standard Tcl
list with one of the following forms:
name\0[fgColor\0[bgColor]]
Name is the name of a cursor in the standard X cursor font,
i.e., any of the names defined in cursorfont.h, without
the XC_. Some example values are X_cursor, hand2,
or left_ptr. Appendix B of ``The X Window System''
by Scheifler & Gettys has illustrations showing what each of these
cursors looks like. If fgColor and bgColor are both
specified, they give the foreground and background colors to use
for the cursor (any of the forms acceptable to Tk_GetColor
may be used). If only fgColor is specified, then there
will be no background color: the background will be transparent.
If no colors are specified, then the cursor
will use black for its foreground color and white for its background
color.
The Macintosh version of Tk also supports all of the X cursors.
Tk on the Mac will also accept any of the standard Mac cursors
including ibeam, crosshair, watch, plus, and
arrow. In addition, Tk will load Macintosh cursor resources of
the types crsr (color) and CURS (black and white) by the
name of the of the resource. The application and all its open
dynamic library's resource files will be searched for the named
cursor. If there are conflicts color cursors will always be loaded
in preference to black and white cursors.
@sourceName\0maskName\0fgColor\0bgColor
In this form, sourceName and maskName are the names of
files describing bitmaps for the cursor's source bits and mask.
Each file must be in standard X11 or X10 bitmap format.
FgColor and bgColor
indicate the colors to use for the
cursor, in any of the forms acceptable to Tk_GetColor. This
form of the command will not work on Macintosh or Windows computers.
@sourceName\0fgColor
This form is similar to the one above, except that the source is
used as mask also. This means that the cursor's background is
transparent. This form of the command will not work on Macintosh
or Windows computers.
Tk_GetCursorFromData allows cursors to be created from
in-memory descriptions of their source and mask bitmaps. Source
points to standard bitmap data for the cursor's source bits, and
mask points to standard bitmap data describing
which pixels of source are to be drawn and which are to be
considered transparent. Width and height give the
dimensions of the cursor, xHot and yHot indicate the
location of the cursor's hot-spot (the point that is reported when
an event occurs), and fg and bg describe the cursor's
foreground and background colors textually (any of the forms
suitable for Tk_GetColor may be used). Typically, the
arguments to Tk_GetCursorFromData are created by including
a cursor file directly into the source code for a program, as in
the following example:
Tk_Cursor cursor;
#include "source.cursor"
#include "mask.cursor"
cursor = Tk_GetCursorFromData(interp, tkwin, source_bits,
mask_bits, source_width, source_height, source_x_hot,
source_y_hot, Tk_GetUid("red"), Tk_GetUid("blue"));
Under normal conditions, Tk_GetCursor and Tk_GetCursorFromData
will return an identifier for the requested cursor. If an error
occurs in creating the cursor, such as when nameId refers
to a non-existent file, then None is returned and an error
message will be stored in interp->result.
Tk_GetCursor and Tk_GetCursorFromData maintain a
database of all the cursors they have created. Whenever possible,
a call to Tk_GetCursor or Tk_GetCursorFromData will
return an existing cursor rather than creating a new one. This
approach can substantially reduce server overhead, so the Tk
procedures should generally be used in preference to Xlib procedures
like XCreateFontCursor or XCreatePixmapCursor, which
create a new cursor on each call.
The procedure Tk_NameOfCursor is roughly the inverse of
Tk_GetCursor. If its cursor argument was created
by Tk_GetCursor, then the return value is the nameId
argument that was passed to Tk_GetCursor to create the
cursor. If cursor was created by a call to Tk_GetCursorFromData,
or by any other mechanism, then the return value is a hexadecimal string
giving the X identifier for the cursor.
Note: the string returned by Tk_NameOfCursor is
only guaranteed to persist until the next call to
Tk_NameOfCursor. Also, this call is not portable except for
cursors returned by Tk_GetCursor.
When a cursor returned by Tk_GetCursor or Tk_GetCursorFromData
is no longer needed, Tk_FreeCursor should be called to release it.
There should be exactly one call to Tk_FreeCursor for
each call to Tk_GetCursor or Tk_GetCursorFromData.
When a cursor is no longer in use anywhere (i.e. it has been freed as
many times as it has been gotten) Tk_FreeCursor will release
it to the X server and remove it from the database.
BUGS
In determining whether an existing cursor can be used to satisfy
a new request, Tk_GetCursor and Tk_GetCursorFromData
consider only the immediate values of their arguments. For
example, when a file name is passed to Tk_GetCursor,
Tk_GetCursor will assume it is safe to re-use an existing
cursor created from the same file name: it will not check to
see whether the file itself has changed, or whether the current
directory has changed, thereby causing the name to refer to
a different file. Similarly, Tk_GetCursorFromData assumes
that if the same source pointer is used in two different calls,
then the pointers refer to the same data; it does not check to
see if the actual data values have changed.
KEYWORDS
cursor
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