1Tk_AllocCursorFromObj(3)     Tk Library Procedures    Tk_AllocCursorFromObj(3)
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5______________________________________________________________________________
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NAME

8       Tk_AllocCursorFromObj, Tk_GetCursor, Tk_GetCursorFromObj, Tk_GetCursor‐
9       FromData, Tk_NameOfCursor, Tk_FreeCursorFromObj, Tk_FreeCursor -  main‐
10       tain database of cursors
11

SYNOPSIS

13       #include <tk.h>
14
15       Tk_Cursor
16       Tk_AllocCursorFromObj(interp, tkwin, objPtr)
17
18       Tk_Cursor
19       Tk_GetCursor(interp, tkwin, name)
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21       Tk_Cursor
22       Tk_GetCursorFromObj(tkwin, objPtr)
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24       Tk_Cursor
25       Tk_GetCursorFromData(interp, tkwin, source, mask, width, height, xHot, yHot, fg, bg)
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27       const char *
28       Tk_NameOfCursor(display, cursor)
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30       Tk_FreeCursorFromObj(tkwin, objPtr)
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32       Tk_FreeCursor(display, cursor)
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ARGUMENTS

35       Tcl_Interp *interp (in)               Interpreter   to  use  for  error
36                                             reporting.
37
38       Tk_Window tkwin (in)                  Token for  window  in  which  the
39                                             cursor will be used.
40
41       Tcl_Obj *objPtr (in/out)              Description of cursor;  see below
42                                             for  possible  values.   Internal
43                                             rep  will  be  modified  to cache
44                                             pointer to corresponding  Tk_Cur‐
45                                             sor.
46
47       char *name (in)                       Same as objPtr except description
48                                             of cursor is passed as  a  string
49                                             and  resulting  Tk_Cursor  is not
50                                             cached.
51
52       const char *source (in)               Data for cursor cursor, in  stan‐
53                                             dard cursor format.
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55       const char *mask (in)                 Data for mask cursor, in standard
56                                             cursor format.
57
58       int width (in)                        Width of source and mask.
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60       int height (in)                       Height of source and mask.
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62       int xHot (in)                         X-location of cursor hot-spot.
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64       int yHot (in)                         Y-location of cursor hot-spot.
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66       Tk_Uid fg (in)                        Textual description of foreground
67                                             color for cursor.
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69       Tk_Uid bg (in)                        Textual description of background
70                                             color for cursor.
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72       Display *display (in)                 Display  for  which  cursor   was
73                                             allocated.
74
75       Tk_Cursor cursor (in)                 Opaque  Tk identifier for cursor.
76                                             If passed to Tk_FreeCursor,  must
77                                             have been returned by some previ‐
78                                             ous  call  to   Tk_GetCursor   or
79                                             Tk_GetCursorFromData.
80______________________________________________________________________________
81

DESCRIPTION

83       These procedures manage a collection of cursors being used by an appli‐
84       cation.  The  procedures  allow  cursors  to  be  re-used  efficiently,
85       thereby  avoiding  server  overhead, and also allow cursors to be named
86       with character strings.
87
88       Tk_AllocCursorFromObj takes as argument an object describing a  cursor,
89       and  returns  an opaque Tk identifier for a cursor corresponding to the
90       description.  It re-uses an existing cursor if possible and  creates  a
91       new  one otherwise.  Tk_AllocCursorFromObj caches information about the
92       return value in objPtr, which speeds up future calls to procedures such
93       as Tk_AllocCursorFromObj and Tk_GetCursorFromObj. If an error occurs in
94       creating the cursor, such as when objPtr refers to a non-existent file,
95       then  None  is returned and an error message will be stored in interp's
96       result if interp is not NULL.  ObjPtr must contain a standard Tcl  list
97       with one of the following forms:
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99       name [fgColor [bgColor]]
100              Name  is  the  name of a cursor in the standard X cursor cursor,
101              i.e., any of the names defined in  cursorcursor.h,  without  the
102              XC_.  Some example values are X_cursor, hand2, or left_ptr.  Ap‐
103              pendix B of “The X Window System”  by  Scheifler  &  Gettys  has
104              illustrations showing what each of these cursors looks like.  If
105              fgColor and bgColor are both specified, they give the foreground
106              and  background  colors  to use for the cursor (any of the forms
107              acceptable to Tk_GetColor may be  used).   If  only  fgColor  is
108              specified,  then  there  will be no background color:  the back‐
109              ground will be transparent.  If no colors  are  specified,  then
110              the cursor will use black for its foreground color and white for
111              its background color.
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113              The Macintosh version of Tk supports all of the  X  cursors  and
114              will  also  accept  any  of  the  standard Mac cursors including
115              ibeam, crosshair, watch, plus, and arrow.  In addition, Tk  will
116              load  Macintosh  cursor  resources of the types crsr (color) and
117              CURS (black and white) by the name of the resource.  The  appli‐
118              cation and all its open dynamic library's resource files will be
119              searched for the named cursor.  If  there  are  conflicts  color
120              cursors  will  always be loaded in preference to black and white
121              cursors.
122
123       @sourceName maskName fgColor bgColor
124              In this form, sourceName and maskName are  the  names  of  files
125              describing  cursors for the cursor's source bits and mask.  Each
126              file must be in standard X11 cursor format.  FgColor and bgColor
127              indicate  the  colors to use for the cursor, in any of the forms
128              acceptable to Tk_GetColor.  This form of the  command  will  not
129              work on Macintosh or Windows computers.
130
131       @sourceName fgColor
132              This form is similar to the one above, except that the source is
133              used as mask also.  This means that the cursor's  background  is
134              transparent.   This  form of the command will not work on Macin‐
135              tosh or Windows computers.
136
137       @sourceName
138              This form only works on Windows, and will load a Windows  system
139              cursor (.ani or .cur) from the file specified in sourceName.
140
141       Tk_GetCursor  is  identical  to  Tk_AllocCursorFromObj  except that the
142       description of the cursor is specified with  a  string  instead  of  an
143       object.   This  prevents Tk_GetCursor from caching the return value, so
144       Tk_GetCursor is less efficient than Tk_AllocCursorFromObj.
145
146       Tk_GetCursorFromObj returns the token for an existing cursor, given the
147       window  and description used to create the cursor.  Tk_GetCursorFromObj
148       does not actually create the cursor; the cursor must already have  been
149       created  with a previous call to Tk_AllocCursorFromObj or Tk_GetCursor.
150       The return value is cached in objPtr, which speeds up future  calls  to
151       Tk_GetCursorFromObj with the same objPtr and tkwin.
152
153       Tk_GetCursorFromData  allows  cursors  to  be  created  from  in-memory
154       descriptions of their source and mask cursors.  Source points to  stan‐
155       dard cursor data for the cursor's source bits, and mask points to stan‐
156       dard cursor data describing which pixels of source are to be drawn  and
157       which  are  to  be  considered  transparent.  Width and height give the
158       dimensions of the cursor, xHot and yHot indicate the  location  of  the
159       cursor's  hot-spot  (the  point that is reported when an event occurs),
160       and fg and bg describe the cursor's foreground  and  background  colors
161       textually  (any  of  the  forms  suitable for Tk_GetColor may be used).
162       Typically, the arguments to Tk_GetCursorFromData are created by includ‐
163       ing  a  cursor  file directly into the source code for a program, as in
164       the following example:
165              Tk_Cursor cursor;
166              #include "source.cursor"
167              #include "mask.cursor"
168              cursor = Tk_GetCursorFromData(interp, tkwin, source_bits,
169                  mask_bits, source_width, source_height, source_x_hot,
170                  source_y_hot, Tk_GetUid("red"), Tk_GetUid("blue"));
171
172       Under normal conditions Tk_GetCursorFromData will return an  identifier
173       for  the  requested  cursor.  If an error occurs in creating the cursor
174       then None is returned and an error message will be stored  in  interp's
175       result.
176
177       Tk_AllocCursorFromObj,  Tk_GetCursor, and Tk_GetCursorFromData maintain
178       a database of all the cursors they have created.  Whenever possible,  a
179       call  to  Tk_AllocCursorFromObj,  Tk_GetCursor, or Tk_GetCursorFromData
180       will return an existing cursor rather than creating a  new  one.   This
181       approach can substantially reduce server overhead, so the Tk procedures
182       should generally be used in preference to Xlib procedures like XCreate‐
183       FontCursor  or  XCreatePixmapCursor,  which create a new cursor on each
184       call.  The Tk procedures are also more portable than the lower-level  X
185       procedures.
186
187       The  procedure  Tk_NameOfCursor is roughly the inverse of Tk_GetCursor.
188       If its cursor argument was created by  Tk_GetCursor,  then  the  return
189       value  is  the  name argument that was passed to Tk_GetCursor to create
190       the cursor.  If cursor was created by a call  to  Tk_GetCursorFromData,
191       or  by  any  other  mechanism,  then  the return value is a hexadecimal
192       string giving the X identifier  for  the  cursor.   Note:   the  string
193       returned  by  Tk_NameOfCursor  is  only guaranteed to persist until the
194       next call to Tk_NameOfCursor.  Also, this call is not  portable  except
195       for cursors returned by Tk_GetCursor.
196
197       When  a  cursor  returned  by  Tk_AllocCursorFromObj,  Tk_GetCursor, or
198       Tk_GetCursorFromData  is  no  longer  needed,  Tk_FreeCursorFromObj  or
199       Tk_FreeCursor should be called to release it.  For Tk_FreeCursorFromObj
200       the cursor to release is specified with the same  information  used  to
201       create  it;  for  Tk_FreeCursor the cursor to release is specified with
202       its Tk_Cursor token.  There should be exactly one call to Tk_FreeCursor
203       for  each call to Tk_AllocCursorFromObj, Tk_GetCursor, or Tk_GetCursor‐
204       FromData.
205

BUGS

207       In determining whether an existing cursor can be used to satisfy a  new
208       request,  Tk_AllocCursorFromObj, Tk_GetCursor, and Tk_GetCursorFromData
209       consider only the immediate values of their  arguments.   For  example,
210       when a file name is passed to Tk_GetCursor, Tk_GetCursor will assume it
211       is safe to re-use an existing cursor created from the same  file  name:
212       it  will  not  check  to  see  whether  the file itself has changed, or
213       whether the current directory has changed, thereby causing the name  to
214       refer  to  a  different  file.  Similarly, Tk_GetCursorFromData assumes
215       that if the same source pointer is used in two  different  calls,  then
216       the  pointers  refer to the same data;  it does not check to see if the
217       actual data values have changed.
218

KEYWORDS

220       cursor
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223
224Tk                                    8.1             Tk_AllocCursorFromObj(3)
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