src/w16select.c

   1 /* 16-bit Windows Selection processing for emacs on MS-Windows
   2
   3 Copyright (C) 1996-1997, 2001-2014 Free Software Foundation, Inc.
   4
   5 This file is part of GNU Emacs.
   6
   7 GNU Emacs is free software: you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation, either version 3 of the License, or
  10 (at your option) any later version.
  11
  12 GNU Emacs is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 /* These functions work by using WinOldAp interface.  WinOldAp
  21    (WINOLDAP.MOD) is a Microsoft Windows extension supporting
  22    "old" (character-mode) application access to Dynamic Data Exchange,
  23    menus, and the Windows clipboard.  */
  24
  25 /* Written by Dale P. Smith <dpsm@en.com>  */
  26 /* Adapted to DJGPP by Eli Zaretskii <eliz@gnu.org>  */
  27
  28 #ifdef MSDOS
  29
  30 #include <config.h>
  31 #include <dpmi.h>
  32 #include <go32.h>
  33 #include <sys/farptr.h>
  34 #include "lisp.h"
  35 #include "dispextern.h" /* frame.h seems to want this */
  36 #include "frame.h"      /* Need this to get the X window of selected_frame */
  37 #include "blockinput.h"
  38 #include "character.h"
  39 #include "buffer.h"
  40 #include "coding.h"
  41 #include "composite.h"
  42
  43 /* If ever some function outside this file will need to call any
  44    clipboard-related function, the following prototypes and constants
  45    should be put on a header file.  Right now, nobody else uses them.  */
  46
  47 #define CF_TEXT      0x01
  48 #define CF_BITMAP    0x02
  49 #define CF_METAFILE  0x03
  50 #define CF_SYLK      0x04
  51 #define CF_DIF       0x05
  52 #define CF_TIFF      0x06
  53 #define CF_OEMTEXT   0x07
  54 #define CF_DIBBITMAP 0x08
  55 #define CF_WINWRITE  0x80
  56 #define CF_DSPTEXT   0x81
  57 #define CF_DSPBITMAP 0x82
  58
  59 unsigned identify_winoldap_version (void);
  60 unsigned open_clipboard (void);
  61 unsigned empty_clipboard (void);
  62 unsigned set_clipboard_data (unsigned, void *, unsigned, int);
  63 unsigned get_clipboard_data_size (unsigned);
  64 unsigned get_clipboard_data (unsigned, void *, unsigned, int);
  65 unsigned close_clipboard (void);
  66 unsigned clipboard_compact (unsigned);
  67
  68 Lisp_Object QCLIPBOARD, QPRIMARY;
  69
  70 /* The segment address and the size of the buffer in low
  71    memory used to move data between us and WinOldAp module.  */
  72 static struct {
  73   unsigned long size;
  74   unsigned short rm_segment;
  75 } clipboard_xfer_buf_info;
  76
  77 /* The last text we put into the clipboard.  This is used to prevent
  78    passing back our own text from the clipboard, instead of using the
  79    kill ring.  The former is undesirable because the clipboard data
  80    could be MULEtilated by inappropriately chosen
  81    (next-)selection-coding-system.  For this reason, we must store the
  82    text *after* it was encoded/Unix-to-DOS-converted.  */
  83 static unsigned char *last_clipboard_text;
  84
  85 /* The size of allocated storage for storing the clipboard data.  */
  86 static size_t clipboard_storage_size;
  87 \f
  88 /* C functions to access the Windows 3.1x clipboard from DOS apps.
  89
  90    The information was obtained from the Microsoft Knowledge Base,
  91    article Q67675 and can be found at:
  92    http://www.microsoft.com/kb/developr/win_dk/q67675.htm  */
  93
  94 /* See also Ralf Brown's Interrupt List.
  95
  96    I also seem to remember reading about this in Dr. Dobbs Journal a
  97    while ago, but if you knew my memory...  :-)
  98
  99    Dale P. Smith <dpsm@en.com> */
 100
 101 /* Return the WinOldAp support version, or 0x1700 if not supported.  */
 102 unsigned
 103 identify_winoldap_version (void)
 104 {
 105   __dpmi_regs regs;
 106
 107   /* Calls Int 2Fh/AX=1700h
 108      Return Values   AX == 1700H: Clipboard functions not available
 109                         <> 1700H: AL = Major version number
 110                                   AH = Minor version number */
 111   regs.x.ax = 0x1700;
 112   __dpmi_int (0x2f, &regs);
 113   return regs.x.ax;
 114 }
 115
 116 /* Open the clipboard, return non-zero if successful.  */
 117 unsigned
 118 open_clipboard (void)
 119 {
 120   __dpmi_regs regs;
 121
 122   /* Is WINOLDAP supported?  */
 123   /* Kludge alert!!  If WinOldAp is not supported, we return a 0,
 124      which is the same as ``Clipboard already open''.  Currently,
 125      this is taken as an error by all the functions that use
 126      `open_clipboard', but if somebody someday will use that ``open''
 127      clipboard, they will have interesting time debugging it...  */
 128   if (identify_winoldap_version () == 0x1700)
 129     return 0;
 130
 131   /* Calls Int 2Fh/AX=1701h
 132      Return Values   AX == 0: Clipboard already open
 133                         <> 0: Clipboard opened */
 134   regs.x.ax = 0x1701;
 135   __dpmi_int (0x2f, &regs);
 136   return regs.x.ax;
 137 }
 138
 139 /* Empty clipboard, return non-zero if successful.  */
 140 unsigned
 141 empty_clipboard (void)
 142 {
 143   __dpmi_regs regs;
 144
 145   /* Calls Int 2Fh/AX=1702h
 146      Return Values   AX == 0: Error occurred
 147                         <> 0: OK, Clipboard emptied */
 148   regs.x.ax = 0x1702;
 149   __dpmi_int (0x2f, &regs);
 150   return regs.x.ax;
 151 }
 152
 153 /* Ensure we have a buffer in low memory with enough memory for data
 154    of size WANT_SIZE.  Return the linear address of the buffer.  */
 155 static unsigned long
 156 alloc_xfer_buf (unsigned want_size)
 157 {
 158   __dpmi_regs regs;
 159
 160   /* If the usual DJGPP transfer buffer is large enough, use that.  */
 161   if (want_size <= _go32_info_block.size_of_transfer_buffer)
 162     return __tb & 0xfffff;
 163
 164   /* Don't even try to allocate more than 1MB of memory: DOS cannot
 165      possibly handle that (it will overflow the BX register below).  */
 166   if (want_size > 0xfffff)
 167     return 0;
 168
 169   /* Need size rounded up to the nearest paragraph, and in
 170      paragraph units (1 paragraph = 16 bytes).  */
 171   clipboard_xfer_buf_info.size = (want_size + 15) >> 4;
 172
 173   /* The NT DPMI host crashes us if we free DOS memory via the
 174      DPMI service.  Work around by calling DOS allocate/free block.  */
 175   regs.h.ah = 0x48;
 176   regs.x.bx = clipboard_xfer_buf_info.size;
 177   __dpmi_int (0x21, &regs);
 178   if (regs.x.flags & 1)
 179     {
 180       clipboard_xfer_buf_info.size = 0;
 181       return 0;
 182     }
 183
 184   clipboard_xfer_buf_info.rm_segment = regs.x.ax;
 185   return (((int)clipboard_xfer_buf_info.rm_segment) << 4) & 0xfffff;
 186 }
 187
 188 /* Free our clipboard buffer.  We always free it after use, because
 189    keeping it leaves less free conventional memory for subprocesses.
 190    The clipboard buffer tends to be large in size, because for small
 191    clipboard data sizes we use the DJGPP transfer buffer.  */
 192 static void
 193 free_xfer_buf (void)
 194 {
 195   /* If the size is 0, we used DJGPP transfer buffer, so don't free.  */
 196   if (clipboard_xfer_buf_info.size)
 197     {
 198       __dpmi_regs regs;
 199
 200       /* The NT DPMI host crashes us if we free DOS memory via
 201          the DPMI service.  Work around by calling DOS free block.  */
 202       regs.h.ah = 0x49;
 203       regs.x.es = clipboard_xfer_buf_info.rm_segment;
 204       __dpmi_int (0x21, &regs);
 205       clipboard_xfer_buf_info.size = 0;
 206     }
 207 }
 208
 209 /* Copy data into the clipboard, return zero if successful.  */
 210 unsigned
 211 set_clipboard_data (unsigned Format, void *Data, unsigned Size, int Raw)
 212 {
 213   __dpmi_regs regs;
 214   unsigned truelen;
 215   unsigned long xbuf_addr, buf_offset;
 216   unsigned char *dp = Data, *dstart = dp;
 217
 218   if (Format != CF_OEMTEXT)
 219     return 3;
 220
 221   /* need to know final size after '\r' chars are inserted (the
 222      standard CF_OEMTEXT clipboard format uses CRLF line endings,
 223      while Emacs uses just LF internally).  */
 224   truelen = Size + 1;           /* +1 for the terminating null */
 225
 226   if (!Raw)
 227     {
 228       /* avoid using strchr because it recomputes the length everytime */
 229       while ((dp = memchr (dp, '\n', Size - (dp - dstart))) != 0)
 230         {
 231           truelen++;
 232           dp++;
 233         }
 234     }
 235
 236   if (clipboard_compact (truelen) < truelen)
 237     return 1;
 238
 239   if ((xbuf_addr = alloc_xfer_buf (truelen)) == 0)
 240     return 1;
 241
 242   /* Move the buffer into the low memory, convert LF into CR-LF if needed.  */
 243   if (Raw)
 244     {
 245       dosmemput (Data, Size, xbuf_addr);
 246
 247       /* Terminate with a null, otherwise Windows does strange things
 248          when the text size is an integral multiple of 32 bytes. */
 249       _farpokeb (_dos_ds, xbuf_addr + Size, '\0');
 250     }
 251   else
 252     {
 253       dp = Data;
 254       buf_offset = xbuf_addr;
 255       _farsetsel (_dos_ds);
 256       while (Size--)
 257         {
 258           /* Don't allow them to put binary data into the clipboard, since
 259              it will cause yanked data to be truncated at the first null.  */
 260           if (*dp == '\0')
 261             return 2;
 262           if (*dp == '\n')
 263             _farnspokeb (buf_offset++, '\r');
 264           _farnspokeb (buf_offset++, *dp++);
 265         }
 266
 267       /* Terminate with a null, otherwise Windows does strange things
 268          when the text size is an integral multiple of 32 bytes. */
 269       _farnspokeb (buf_offset, '\0');
 270     }
 271
 272   /* Stash away the data we are about to put into the clipboard, so we
 273      could later check inside get_clipboard_data whether the clipboard
 274      still holds our data.  */
 275   if (clipboard_storage_size < truelen)
 276     {
 277       clipboard_storage_size = truelen + 100;
 278       last_clipboard_text =
 279         (char *) xrealloc (last_clipboard_text, clipboard_storage_size);
 280     }
 281   if (last_clipboard_text)
 282     dosmemget (xbuf_addr, truelen, last_clipboard_text);
 283
 284   /* Calls Int 2Fh/AX=1703h with:
 285                      DX = WinOldAp-Supported Clipboard format
 286                      ES:BX = Pointer to data
 287                      SI:CX = Size of data in bytes
 288      Return Values   AX == 0: Error occurred
 289                         <> 0: OK.  Data copied into the Clipboard.  */
 290   regs.x.ax = 0x1703;
 291   regs.x.dx = Format;
 292   regs.x.si = truelen >> 16;
 293   regs.x.cx = truelen & 0xffff;
 294   regs.x.es = xbuf_addr >> 4;
 295   regs.x.bx = xbuf_addr & 15;
 296   __dpmi_int (0x2f, &regs);
 297
 298   free_xfer_buf ();
 299
 300   /* If the above failed, invalidate the local copy of the clipboard.  */
 301   if (regs.x.ax == 0)
 302     *last_clipboard_text = '\0';
 303
 304   /* Zero means success, otherwise (1, 2, or 3) it's an error.  */
 305   return regs.x.ax > 0 ? 0 : 3;
 306 }
 307
 308 /* Return the size of the clipboard data of format FORMAT.  */
 309 unsigned
 310 get_clipboard_data_size (unsigned Format)
 311 {
 312   __dpmi_regs regs;
 313
 314   /* Calls Int 2Fh/AX=1704h with:
 315                      DX = WinOldAp-Supported Clipboard format
 316      Return Values   DX:AX == Size of the data in bytes, including any
 317                               headers.
 318                            == 0 If data in this format is not in
 319                            the clipboard.  */
 320   regs.x.ax = 0x1704;
 321   regs.x.dx = Format;
 322   __dpmi_int (0x2f, &regs);
 323   return ( (((unsigned)regs.x.dx) << 16) | regs.x.ax);
 324 }
 325
 326 /* Get clipboard data, return its length.
 327    Warning: this doesn't check whether DATA has enough space to hold
 328    SIZE bytes.  */
 329 unsigned
 330 get_clipboard_data (unsigned Format, void *Data, unsigned Size, int Raw)
 331 {
 332   __dpmi_regs regs;
 333   unsigned long xbuf_addr;
 334   unsigned char *dp = Data;
 335
 336   if (Format != CF_OEMTEXT)
 337     return 0;
 338
 339   if (Size == 0)
 340     return 0;
 341
 342   if ((xbuf_addr = alloc_xfer_buf (Size)) == 0)
 343     return 0;
 344
 345   /* Calls Int 2Fh/AX=1705h with:
 346                      DX = WinOldAp-Supported Clipboard format
 347                      ES:BX = Pointer to data buffer to hold data
 348      Return Values   AX == 0: Error occurred (or data in this format is not
 349                               in the clipboard)
 350                         <> 0: OK  */
 351   regs.x.ax = 0x1705;
 352   regs.x.dx = Format;
 353   regs.x.es = xbuf_addr >> 4;
 354   regs.x.bx = xbuf_addr & 15;
 355   __dpmi_int (0x2f, &regs);
 356   if (regs.x.ax != 0)
 357     {
 358       unsigned char null_char = '\0';
 359       unsigned long xbuf_beg = xbuf_addr;
 360
 361       /* If last_clipboard_text is NULL, we don't want to slow down
 362          the next loop by an additional test.  */
 363       register unsigned char *lcdp =
 364         last_clipboard_text == NULL ? &null_char : last_clipboard_text;
 365
 366       /* Copy data from low memory, remove CR
 367          characters before LF if needed.  */
 368       _farsetsel (_dos_ds);
 369       while (Size--)
 370         {
 371           register unsigned char c = _farnspeekb (xbuf_addr++);
 372
 373           if (*lcdp == c)
 374             lcdp++;
 375
 376           if ((*dp++ = c) == '\r' && !Raw && _farnspeekb (xbuf_addr) == '\n')
 377             {
 378               dp--;
 379               *dp++ = '\n';
 380               xbuf_addr++;
 381               if (*lcdp == '\n')
 382                 lcdp++;
 383             }
 384           /* Windows reportedly rounds up the size of clipboard data
 385              (passed in SIZE) to a multiple of 32, and removes trailing
 386              spaces from each line without updating SIZE.  We therefore
 387              bail out when we see the first null character.  */
 388           else if (c == '\0')
 389             break;
 390         }
 391
 392       /* If the text in clipboard is identical to what we put there
 393          last time set_clipboard_data was called, pretend there's no
 394          data in the clipboard.  This is so we don't pass our own text
 395          from the clipboard (which might be troublesome if the killed
 396          text includes null characters).  */
 397       if (last_clipboard_text &&
 398           xbuf_addr - xbuf_beg == (long)(lcdp - last_clipboard_text))
 399         dp = (unsigned char *)Data + 1;
 400     }
 401
 402   free_xfer_buf ();
 403
 404   return (unsigned) (dp - (unsigned char *)Data - 1);
 405 }
 406
 407 /* Close clipboard, return non-zero if successful.  */
 408 unsigned
 409 close_clipboard (void)
 410 {
 411   __dpmi_regs regs;
 412
 413   /* Calls Int 2Fh/AX=1708h
 414      Return Values   AX == 0: Error occurred
 415                         <> 0: OK */
 416   regs.x.ax = 0x1708;
 417   __dpmi_int (0x2f, &regs);
 418   return regs.x.ax;
 419 }
 420
 421 /* Compact clipboard data so that at least SIZE bytes is available.  */
 422 unsigned
 423 clipboard_compact (unsigned Size)
 424 {
 425   __dpmi_regs regs;
 426
 427   /* Calls Int 2Fh/AX=1709H with:
 428                      SI:CX = Desired memory size in bytes.
 429      Return Values   DX:AX == Number of bytes of largest block of free memory.
 430                            == 0 if error or no memory  */
 431   regs.x.ax = 0x1709;
 432   regs.x.si = Size >> 16;
 433   regs.x.cx = Size & 0xffff;
 434   __dpmi_int (0x2f, &regs);
 435   return ((unsigned)regs.x.dx << 16) | regs.x.ax;
 436 }
 437 \f
 438 static char no_mem_msg[] =
 439   "(Not enough DOS memory to put saved text into clipboard.)";
 440 static char binary_msg[] =
 441   "(Binary characters in saved text; clipboard data not set.)";
 442 static char system_error_msg[] =
 443   "(Clipboard interface failure; clipboard data not set.)";
 444
 445 DEFUN ("w16-set-clipboard-data", Fw16_set_clipboard_data, Sw16_set_clipboard_data, 1, 2, 0,
 446        doc: /* This sets the clipboard data to the given text.  */)
 447   (Lisp_Object string, Lisp_Object frame)
 448 {
 449   unsigned ok = 1, put_status = 0;
 450   int nbytes, no_crlf_conversion;
 451   unsigned char *src, *dst = NULL;
 452
 453   CHECK_STRING (string);
 454
 455   if (!FRAME_MSDOS_P (decode_live_frame (frame)))
 456     goto done;
 457
 458   block_input ();
 459
 460   if (!open_clipboard ())
 461     goto error;
 462
 463   nbytes = SBYTES (string);
 464   src = SDATA (string);
 465
 466   /* Do we need to encode this text?  */
 467   for (dst = src; dst < src + nbytes; dst++)
 468     {
 469       if (*dst == '\0' || *dst >= 0x80)
 470         break;
 471     }
 472   if (dst >= src + nbytes)
 473     {
 474       /* No multibyte characters in text.  We need not encode it, but we
 475          will have to convert it to DOS CR-LF style.  */
 476       no_crlf_conversion = 0;
 477       Vlast_coding_system_used = Qraw_text;
 478       dst = NULL;       /* so we don't try to free a random pointer */
 479     }
 480   else
 481     {
 482       /* We must encode contents of STRING according to what
 483          clipboard-coding-system specifies.  */
 484       struct coding_system coding;
 485       Lisp_Object coding_system =
 486         NILP (Vnext_selection_coding_system) ?
 487         Vselection_coding_system : Vnext_selection_coding_system;
 488
 489       setup_coding_system (Fcheck_coding_system (coding_system), &coding);
 490       coding.dst_bytes = nbytes * 4;
 491       coding.destination = xmalloc (coding.dst_bytes);
 492       Vnext_selection_coding_system = Qnil;
 493       coding.mode |= CODING_MODE_LAST_BLOCK;
 494       dst = coding.destination;
 495       encode_coding_object (&coding, string, 0, 0,
 496                             SCHARS (string), nbytes, Qnil);
 497       no_crlf_conversion = 1;
 498       nbytes = coding.produced;
 499       Vlast_coding_system_used = CODING_ID_NAME (coding.id);
 500       src = dst;
 501     }
 502
 503   ok = empty_clipboard ()
 504     && ((put_status
 505          = set_clipboard_data (CF_OEMTEXT, src, nbytes, no_crlf_conversion))
 506         == 0);
 507
 508   if (!no_crlf_conversion)
 509   close_clipboard ();
 510
 511   if (ok) goto unblock;
 512
 513  error:
 514
 515   ok = 0;
 516
 517  unblock:
 518   xfree (dst);
 519   unblock_input ();
 520
 521   /* Notify user if the text is too large to fit into DOS memory.
 522      (This will happen somewhere after 600K bytes (470K in DJGPP v1.x),
 523      depending on user system configuration.)  If we just silently
 524      fail the function, people might wonder why their text sometimes
 525      doesn't make it to the clipboard.  */
 526   if (put_status)
 527     {
 528       switch (put_status)
 529         {
 530           case 1:
 531             message3 (make_unibyte_string (no_mem_msg, sizeof (no_mem_msg) - 1));
 532             break;
 533           case 2:
 534             message3 (make_unibyte_string (binary_msg, sizeof (binary_msg) - 1));
 535             break;
 536           case 3:
 537             message3 (make_unibyte_string (system_error_msg, sizeof (system_error_msg) - 1));
 538             break;
 539         }
 540       sit_for (make_number (2), 0, 2);
 541     }
 542
 543  done:
 544
 545   return (ok && put_status == 0 ? string : Qnil);
 546 }
 547
 548 DEFUN ("w16-get-clipboard-data", Fw16_get_clipboard_data, Sw16_get_clipboard_data, 0, 1, 0,
 549        doc: /* This gets the clipboard data in text format.  */)
 550   (Lisp_Object frame)
 551 {
 552   unsigned data_size, truelen;
 553   unsigned char *htext = NULL;
 554   Lisp_Object ret = Qnil;
 555   int require_decoding = 0;
 556
 557   if (!FRAME_MSDOS_P (decode_live_frame (frame)))
 558     goto done;
 559
 560   block_input ();
 561
 562   if (!open_clipboard ())
 563     goto unblock;
 564
 565   if ((data_size = get_clipboard_data_size (CF_OEMTEXT)) == 0 ||
 566       (htext = xmalloc (data_size)) == 0)
 567     goto closeclip;
 568
 569   /* need to know final size after '\r' chars are removed because
 570      we can't change the string size manually, and doing an extra
 571      copy is silly */
 572   if ((truelen = get_clipboard_data (CF_OEMTEXT, htext, data_size, 0)) == 0)
 573     goto closeclip;
 574
 575   /* Do we need to decode it?  */
 576   {
 577     /* If the clipboard data contains any 8-bit Latin-1 code, we
 578        need to decode it.  */
 579     int i;
 580
 581     for (i = 0; i < truelen; i++)
 582       {
 583         if (htext[i] >= 0x80)
 584           {
 585             require_decoding = 1;
 586             break;
 587           }
 588       }
 589   }
 590   if (require_decoding)
 591     {
 592       struct coding_system coding;
 593       Lisp_Object coding_system = Vnext_selection_coding_system;
 594
 595       truelen = get_clipboard_data (CF_OEMTEXT, htext, data_size, 1);
 596       if (NILP (coding_system))
 597         coding_system = Vselection_coding_system;
 598       setup_coding_system (Fcheck_coding_system (coding_system), &coding);
 599       coding.source = htext;
 600       coding.mode |= CODING_MODE_LAST_BLOCK;
 601       /* We explicitly disable composition handling because selection
 602          data should not contain any composition sequence.  */
 603       coding.mode &= CODING_ANNOTATION_MASK;
 604       decode_coding_object (&coding, Qnil, 0, 0, truelen, truelen, Qt);
 605       ret = coding.dst_object;
 606       Vlast_coding_system_used = CODING_ID_NAME (coding.id);
 607     }
 608   else
 609     {
 610       ret = make_unibyte_string ((char *) htext, truelen);
 611       Vlast_coding_system_used = Qraw_text;
 612     }
 613
 614   xfree (htext);
 615   Vnext_selection_coding_system = Qnil;
 616
 617  closeclip:
 618   close_clipboard ();
 619
 620  unblock:
 621   unblock_input ();
 622
 623  done:
 624
 625   return (ret);
 626 }
 627
 628 /* Support checking for a clipboard selection. */
 629
 630 DEFUN ("x-selection-exists-p", Fx_selection_exists_p, Sx_selection_exists_p,
 631        0, 2, 0,
 632        doc: /* Whether there is an owner for the given X selection.
 633 SELECTION should be the name of the selection in question, typically
 634 one of the symbols `PRIMARY', `SECONDARY', or `CLIPBOARD'.  (X expects
 635 these literal upper-case names.)  The symbol nil is the same as
 636 `PRIMARY', and t is the same as `SECONDARY'.
 637
 638 TERMINAL should be a terminal object or a frame specifying the X
 639 server to query.  If omitted or nil, that stands for the selected
 640 frame's display, or the first available X display.  */)
 641   (Lisp_Object selection, Lisp_Object terminal)
 642 {
 643   CHECK_SYMBOL (selection);
 644
 645   /* Return nil for SECONDARY selection.  For PRIMARY (or nil)
 646      selection, check if there is some text on the kill-ring;
 647      for CLIPBOARD, check if the clipboard currently has valid
 648      text format contents.
 649
 650      The test for killed text on the kill-ring emulates the Emacs
 651      behavior on X, where killed text is also put into X selection
 652      by the X interface code.  (On MSDOS, killed text is only put
 653      into the clipboard if we run under Windows, so we cannot check
 654      the clipboard alone.)  */
 655   if ((EQ (selection, Qnil) || EQ (selection, QPRIMARY))
 656       && ! NILP (Fsymbol_value (Fintern_soft (build_string ("kill-ring"),
 657                                               Qnil))))
 658     return Qt;
 659
 660   if (EQ (selection, QCLIPBOARD))
 661     {
 662       Lisp_Object val = Qnil;
 663
 664       if (open_clipboard ())
 665         {
 666           if (get_clipboard_data_size (CF_OEMTEXT))
 667             val = Qt;
 668           close_clipboard ();
 669         }
 670       return val;
 671     }
 672   return Qnil;
 673 }
 674
 675 void
 676 syms_of_win16select (void)
 677 {
 678   defsubr (&Sw16_set_clipboard_data);
 679   defsubr (&Sw16_get_clipboard_data);
 680   defsubr (&Sx_selection_exists_p);
 681
 682   DEFVAR_LISP ("selection-coding-system", Vselection_coding_system,
 683                doc: /* Coding system for communicating with other programs.
 684
 685 For MS-Windows and MS-DOS:
 686 When sending or receiving text via selection and clipboard, the text
 687 is encoded or decoded by this coding system.  The default value is
 688 the current system default encoding on 9x/Me, `utf-16le-dos'
 689 \(Unicode) on NT/W2K/XP, and `iso-latin-1-dos' on MS-DOS.
 690
 691 For X Windows:
 692 When sending text via selection and clipboard, if the target
 693 data-type matches with the type of this coding system, it is used
 694 for encoding the text.  Otherwise (including the case that this
 695 variable is nil), a proper coding system is used as below:
 696
 697 data-type       coding system
 698 ---------       -------------
 699 UTF8_STRING     utf-8
 700 COMPOUND_TEXT   compound-text-with-extensions
 701 STRING          iso-latin-1
 702 C_STRING        no-conversion
 703
 704 When receiving text, if this coding system is non-nil, it is used
 705 for decoding regardless of the data-type.  If this is nil, a
 706 proper coding system is used according to the data-type as above.
 707
 708 See also the documentation of the variable `x-select-request-type' how
 709 to control which data-type to request for receiving text.
 710
 711 The default value is nil.  */);
 712   Vselection_coding_system = intern ("iso-latin-1-dos");
 713
 714   DEFVAR_LISP ("next-selection-coding-system", Vnext_selection_coding_system,
 715                doc: /* Coding system for the next communication with other programs.
 716 Usually, `selection-coding-system' is used for communicating with
 717 other programs (X Windows clients or MS Windows programs).  But, if this
 718 variable is set, it is used for the next communication only.
 719 After the communication, this variable is set to nil.  */);
 720   Vnext_selection_coding_system = Qnil;
 721
 722   QPRIMARY   = intern ("PRIMARY");      staticpro (&QPRIMARY);
 723   QCLIPBOARD = intern ("CLIPBOARD");    staticpro (&QCLIPBOARD);
 724 }
 725
 726 #endif /* MSDOS */