Tk_AllocCursorFromObj(3) Tk Library Procedures Tk_AllocCursorFromObj(3)

____________________________________________________________________________

NAME

Tk_AllocCursorFromObj, Tk_GetCursor, Tk_GetCursorFromObj,
Tk_GetCursorFromData, Tk_NameOfCursor, Tk_FreeCursorFromObj,
Tk_FreeCursor - maintain database of cursors

SYNOPSIS

#include <tk.h>

Tk_Cursor
Tk_AllocCursorFromObj(interp, tkwin, objPtr)

Tk_Cursor
Tk_GetCursor(interp, tkwin, name)

Tk_Cursor
Tk_GetCursorFromObj(tkwin, objPtr)

Tk_Cursor
Tk_GetCursorFromData(interp, tkwin, source, mask, width, height, xHot, yHot, fg, bg)

const char *
Tk_NameOfCursor(display, cursor)

Tk_FreeCursorFromObj(tkwin, objPtr)

Tk_FreeCursor(display, cursor)

ARGUMENTS

Tcl_Interp *interp (in) Interpreter to use for error
reporting.

Tk_Window tkwin (in) Token for window in which the
cursor will be used.

Tcl_Obj *objPtr (in/out) Description of cursor; see
below for possible values.
Internal rep will be modified
to cache pointer to
corresponding Tk_Cursor.

const char *name (in) Same as objPtr except
description of cursor is passed
as a string and resulting
Tk_Cursor is not cached.

const char *source (in) Data for cursor cursor, in
standard cursor format.

const char *mask (in) Data for mask cursor, in
standard cursor 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 to
Tk_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.

Tk_AllocCursorFromObj takes as argument an object 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. Tk_AllocCursorFromObj
caches information about the return value in objPtr, which speeds up
future calls to procedures such as Tk_AllocCursorFromObj and
Tk_GetCursorFromObj. If an error occurs in creating the cursor, such
as when objPtr refers to a non-existent file, then None is returned
and an error message will be stored in interp's result if interp is
not NULL. ObjPtr must contain a standard Tcl list with one of the
following forms:

name [fgColor [bgColor]]
Name is the name of a cursor in the standard X cursor cursor,
i.e., any of the names defined in cursorcursor.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 supports all of the X cursors and
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 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 maskName fgColor bgColor
In this form, sourceName and maskName are the names of files
describing cursors for the cursor's source bits and mask.
Each file must be in standard X11 cursor 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 fgColor
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.

@sourceName
This form only works on Windows, and will load a Windows
system cursor (.ani or .cur) from the file specified in
sourceName.

Tk_GetCursor is identical to Tk_AllocCursorFromObj except that the
description of the cursor is specified with a string instead of an
object. This prevents Tk_GetCursor from caching the return value, so
Tk_GetCursor is less efficient than Tk_AllocCursorFromObj.

Tk_GetCursorFromObj returns the token for an existing cursor, given
the window and description used to create the cursor.
Tk_GetCursorFromObj does not actually create the cursor; the cursor
must already have been created with a previous call to
Tk_AllocCursorFromObj or Tk_GetCursor. The return value is cached in
objPtr, which speeds up future calls to Tk_GetCursorFromObj with the
same objPtr and tkwin.

Tk_GetCursorFromData allows cursors to be created from in-memory
descriptions of their source and mask cursors. Source points to
standard cursor data for the cursor's source bits, and mask points to
standard cursor 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_GetCursorFromData will return an
identifier for the requested cursor. If an error occurs in creating
the cursor then None is returned and an error message will be stored
in interp's result.

Tk_AllocCursorFromObj, Tk_GetCursor, and Tk_GetCursorFromData
maintain a database of all the cursors they have created. Whenever
possible, a call to Tk_AllocCursorFromObj, 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 Tk procedures are also
more portable than the lower-level X procedures.

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 name 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 that 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_AllocCursorFromObj, Tk_GetCursor, or
Tk_GetCursorFromData is no longer needed, Tk_FreeCursorFromObj or
Tk_FreeCursor should be called to release it. For
Tk_FreeCursorFromObj the cursor to release is specified with the same
information used to create it; for Tk_FreeCursor the cursor to
release is specified with its Tk_Cursor token. There should be
exactly one call to Tk_FreeCursor for each call to
Tk_AllocCursorFromObj, Tk_GetCursor, or Tk_GetCursorFromData.

BUGS

In determining whether an existing cursor can be used to satisfy a
new request, Tk_AllocCursorFromObj, 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

Tk 8.1 Tk_AllocCursorFromObj(3)