[PATCH] Delayed loading of image libraries

[Juanma Barranquero <jmbarranquero@wke.es>]

OK, this is the (hopefully) final version of the "delayed loading" patch.

It is almost identical to the last one, except for renaming a few things
and adding a missing staticpro that was causing problems on
bootstrapping.  I've added docs to display.texi, and an entry to
etc/NEWS (though I'm, as always, unsure about the right place to put the
entry).  The only thing lacking is ChangeLog entries.

As I said a few days ago, I'd like to install this on trunk, if no one
has objections.

Any comments welcome, of course.

                                                                Juanma




--- old/etc/NEWS	2004-06-10 09:27:32.000000000 +0200
+++ new/etc/NEWS	2004-06-10 13:32:53.000000000 +0200
@@ -17,4 +17,8 @@
 * Installation Changes in Emacs 21.4
 
+** On MS Windows, Emacs now loads the image libraries on demand.
+You can configure the supported image types and their associated dynamic
+libraries by setting the variable `image-library-alist'.
+
 ---
 ** A Bulgarian translation of the Emacs Tutorial is available.
diff -Bru2 old/lisp/image.el new/lisp/image.el
--- old/lisp/image.el	2004-06-10 09:27:54.000000000 +0200
+++ new/lisp/image.el	2004-06-10 11:46:40.000000000 +0200
@@ -49,4 +49,15 @@
 a non-nil value, TYPE is the image's type.")
 
+;;;###autoload
+(defvar image-library-alist nil
+  "Alist of image types vs external libraries needed to display them.
+
+Each element is a list (IMAGE-TYPE LIBRARY...), where the car is a symbol
+representing a supported image type, and the rest are strings giving
+alternate filenames for the corresponding external libraries to load.
+They are tried in the order they appear on the list; if none of them can
+be loaded, the running session of Emacs won't display the image type.
+No entries are needed for pbm and xbm images; they're always supported.")
+;;;###autoload (put 'image-library-alist 'risky-local-variable t)
 
 (defun image-jpeg-p (data)
@@ -112,6 +123,6 @@
   "Value is non-nil if image type TYPE is available.
 Image types are symbols like `xbm' or `jpeg'."
-  (and (boundp 'image-types) (not (null (memq type image-types)))))
-
+  (and (fboundp 'init-image-library)
+       (init-image-library type image-library-alist)))
 
 ;;;###autoload
diff -Bru2 old/lisp/term/w32-win.el new/lisp/term/w32-win.el
--- old/lisp/term/w32-win.el	2004-06-10 09:28:04.000000000 +0200
+++ new/lisp/term/w32-win.el	2004-06-10 11:46:41.000000000 +0200
@@ -1262,4 +1262,12 @@
 	    (error "Font not found")))))
 
+;;; Set default known names for image libraries
+(setq image-library-alist
+      '((xpm "libXpm-nox4.dll" "libxpm.dll")
+        (png "libpng13d.dll" "libpng13.dll" "libpng12d.dll" "libpng12.dll" "libpng.dll")
+        (jpeg "jpeg62.dll" "libjpeg.dll" "jpeg-62.dll" "jpeg.dll")
+        (tiff "libtiff3.dll" "libtiff.dll")
+        (gif "libungif.dll")))
+
 ;;; arch-tag: 69fb1701-28c2-4890-b351-3d1fe4b4f166
 ;;; w32-win.el ends here
diff -Bru2 old/lispref/display.texi new/lispref/display.texi
--- old/lispref/display.texi	2004-06-10 09:28:10.000000000 +0200
+++ new/lispref/display.texi	2004-06-10 13:01:02.000000000 +0200
@@ -2876,6 +2876,11 @@
 
   Emacs can display a number of different image formats; some of them
-are supported only if particular support libraries are installed on your
-machine.  The supported image formats include XBM, XPM (needing the
+are supported only if particular support libraries are installed on
+your machine.  In some environments, Emacs allows loading image
+libraries on demand; if so, the variable @code{image-library-alist}
+can be used to modify the set of known names for these dynamic
+libraries (though it is not posible to add new image formats).
+
+  The supported image formats include XBM, XPM (needing the
 libraries @code{libXpm} version 3.4k and @code{libz}), GIF (needing
 @code{libungif} 4.1.0), Postscript, PBM, JPEG (needing the
@@ -2888,9 +2893,47 @@
 
 @defvar image-types
+@vindex image-types
 This variable contains a list of those image type symbols that are
-supported in the current configuration.
+potentially supported in the current configuration.
+@emph{Potentially} here means that Emacs knows about the image types,
+not necessarily that they can be loaded (they could depend on
+unavailable dynamic libraries, for example).
+
+To know which image types are really available, use
+@code{image-type-available-p}.
+@end defvar
+
+@defvar image-library-alist
+@vindex image-library-alist
+This in an alist of image types vs external libraries needed to
+display them.
+
+Each element is a list @code{(@var{IMAGE-TYPE} @var{LIBRARY}...)},
+where the car is a supported image format from @code{image-types}, and
+the rest are strings giving alternate filenames for the corresponding
+external libraries to load.
+
+They are tried in the order they appear on the list; if none of them
+can be loaded, the running session of Emacs won't support the image
+type.  No entries are needed for @code{pbm} and @code{xbm} images;
+they're always supported.
+
+This variable is ignored if the image libraries are statically linked
+into Emacs.
 @end defvar
 
+@defun  image-type-available-p type
+@findex image-type-available-p
+
+This function returns non-nil if image type TYPE is available, i.e.,
+if images of this type can be loaded and displayed in Emacs.  TYPE
+should be one of the types contained in @code{image-types}.
+
+For image types whose support libraries are statically linked, this
+function always returns @code{t}; for other image types, it returns
+@code{t} if the dynamic library could be loaded, @code{nil} otherwise.
+@end defun
+
 @menu
 * Image Descriptors::   How to specify an image for use in @code{:display}.
--- old/src/dispextern.h	2004-06-10 09:28:19.000000000 +0200
+++ new/src/dispextern.h	2004-06-10 11:46:41.000000000 +0200
@@ -2569,5 +2569,4 @@
 extern int mode_line_in_non_selected_windows;
 extern int redisplaying_p;
-extern Lisp_Object Vimage_types;
 extern void add_to_log P_ ((char *, Lisp_Object, Lisp_Object));
 extern int help_echo_showing_p;
@@ -2655,4 +2654,6 @@
 #ifdef HAVE_WINDOW_SYSTEM
 
+extern Lisp_Object Vimage_types;
+
 extern int x_bitmap_height P_ ((struct frame *, int));
 extern int x_bitmap_width P_ ((struct frame *, int));
diff -Bru2 old/src/image.c new/src/image.c
--- old/src/image.c	2004-06-10 09:28:20.000000000 +0200
+++ new/src/image.c	2004-06-10 11:51:49.000000000 +0200
@@ -606,4 +606,12 @@
 static struct image_type *image_types;
 
+/* A list of symbols, one for each supported image type.  */
+
+Lisp_Object Vimage_types;
+
+/* Cache for delayed-loading image types.  */
+
+static Lisp_Object Vimage_type_cache;
+
 /* The symbol `xbm' which is used as the type symbol for XBM images.  */
 
@@ -630,5 +638,5 @@
 /* Function prototypes.  */
 
-static void define_image_type P_ ((struct image_type *type));
+static Lisp_Object define_image_type P_ ((struct image_type *type, int loaded));
 static struct image_type *lookup_image_type P_ ((Lisp_Object symbol));
 static void image_error P_ ((char *format, Lisp_Object, Lisp_Object));
@@ -638,19 +646,35 @@
 				       Lisp_Object));
 
+#define CACHE_IMAGE_TYPE(type, status) \
+  do { Vimage_type_cache = Fcons (Fcons (type, status), Vimage_type_cache); } while (0)
+
+#define ADD_IMAGE_TYPE(type) \
+  do { Vimage_types = Fcons (type, Vimage_types); } while (0)
 
 /* Define a new image type from TYPE.  This adds a copy of TYPE to
-   image_types and adds the symbol *TYPE->type to Vimage_types.  */
+   image_types and caches the loading status of TYPE.  */
 
-static void
-define_image_type (type)
+static Lisp_Object
+define_image_type (type, loaded)
      struct image_type *type;
+     int loaded;
 {
-  /* Make a copy of TYPE to avoid a bus error in a dumped Emacs.
-     The initialized data segment is read-only.  */
-  struct image_type *p = (struct image_type *) xmalloc (sizeof *p);
-  bcopy (type, p, sizeof *p);
-  p->next = image_types;
-  image_types = p;
-  Vimage_types = Fcons (*p->type, Vimage_types);
+  Lisp_Object success;
+
+  if (!loaded)
+    success = Qnil;
+  else
+    {
+      /* Make a copy of TYPE to avoid a bus error in a dumped Emacs.
+         The initialized data segment is read-only.  */
+      struct image_type *p = (struct image_type *) xmalloc (sizeof *p);
+      bcopy (type, p, sizeof *p);
+      p->next = image_types;
+      image_types = p;
+      success = Qt;
+    }
+
+  CACHE_IMAGE_TYPE(*type->type, success);
+  return success;
 }
 
@@ -1789,4 +1813,31 @@
   }
 
+/* Load a DLL implementing an image type.
+   The `image-library-alist' variable associates a symbol,
+   identifying  an image type, to a list of possible filenames.
+   The function returns NULL if no library could be loaded for
+   the given image type, or if the library was previously loaded;
+   else the handle of the DLL.  */
+static HMODULE
+w32_delayed_load (Lisp_Object libraries, Lisp_Object type)
+{
+  HMODULE library = NULL;
+
+  if (CONSP (libraries) && NILP (Fassq (type, Vimage_type_cache)))
+    {
+      Lisp_Object dlls = Fassq (type, libraries);
+
+      if (CONSP (dlls))
+        for (dlls = XCDR (dlls); CONSP (dlls); dlls = XCDR (dlls))
+          {
+            CHECK_STRING_CAR (dlls);
+            if (library = LoadLibrary (SDATA (XCAR (dlls))))
+              break;
+          }
+    }
+
+  return library;
+}
+
 #endif /* HAVE_NTGUI */
 
@@ -3489,11 +3540,10 @@
 DEF_IMGLIB_FN (XImageFree);
 
-
 static int
-init_xpm_functions (void)
+init_xpm_functions (Lisp_Object libraries)
 {
   HMODULE library;
 
-  if (!(library = LoadLibrary ("libXpm.dll")))
+  if (!(library = w32_delayed_load (libraries, Qxpm)))
     return 0;
 
@@ -5589,19 +5639,10 @@
 
 static int
-init_png_functions (void)
+init_png_functions (Lisp_Object libraries)
 {
   HMODULE library;
 
-  /* Ensure zlib is loaded.  Try debug version first.  */
-  if (!LoadLibrary ("zlibd.dll")
-      && !LoadLibrary ("zlib.dll"))
-    return 0;
-
   /* Try loading libpng under probable names.  */
-  if (!(library = LoadLibrary ("libpng13d.dll"))
-      && !(library = LoadLibrary ("libpng13.dll"))
-      && !(library = LoadLibrary ("libpng12d.dll"))
-      && !(library = LoadLibrary ("libpng12.dll"))
-      && !(library = LoadLibrary ("libpng.dll")))
+  if (!(library = w32_delayed_load (libraries, Qpng)))
     return 0;
 
@@ -6247,11 +6288,9 @@
 
 static int
-init_jpeg_functions (void)
+init_jpeg_functions (Lisp_Object libraries)
 {
   HMODULE library;
 
-  if (!(library = LoadLibrary ("libjpeg.dll"))
-      && !(library = LoadLibrary ("jpeg-62.dll"))
-      && !(library = LoadLibrary ("jpeg.dll")))
+  if (!(library = w32_delayed_load (libraries, Qjpeg)))
     return 0;
 
@@ -6684,9 +6723,9 @@
 
 static int
-init_tiff_functions (void)
+init_tiff_functions (Lisp_Object libraries)
 {
   HMODULE library;
 
-  if (!(library = LoadLibrary ("libtiff.dll")))
+  if (!(library = w32_delayed_load (libraries, Qtiff)))
     return 0;
 
@@ -7104,9 +7143,9 @@
 
 static int
-init_gif_functions (void)
+init_gif_functions (Lisp_Object libraries)
 {
   HMODULE library;
 
-  if (!(library = LoadLibrary ("libungif.dll")))
+  if (!(library = w32_delayed_load (libraries, Qgif)))
     return 0;
 
@@ -7881,7 +7920,79 @@
  ***********************************************************************/
 
+#ifdef HAVE_NTGUI
+/* Image types that rely on external libraries are loaded dynamically
+   if the library is available.  */
+#define CHECK_LIB_AVAILABLE(image_type, init_lib_fn) \
+  define_image_type (image_type, init_lib_fn (libraries))
+#else
+#define CHECK_LIB_AVAILABLE(image_type, init_lib_fn) \
+  define_image_type (image_type, TRUE)
+#endif /* HAVE_NTGUI */
+
+DEFUN ("init-image-library", Finit_image_library, Sinit_image_library, 2, 2, 0,
+       doc: /* Initialize image library implementing image type TYPE.
+Return non-nil if TYPE is a supported image type.
+
+Image types pbm and xbm are prebuilt; other types are loaded here.
+Libraries to load are specified in alist LIBRARIES (usually, the value
+of `image-library-alist', which see.  */)
+  (type, libraries)
+{
+  Lisp_Object tested;
+
+  /* Don't try to reload the library.  */
+  tested = Fassq (type, Vimage_type_cache);
+  if (CONSP (tested))
+    return XCDR (tested);
+
+#if defined (HAVE_XPM) || defined (MAC_OS)
+  if (EQ (type, Qxpm))
+    return CHECK_LIB_AVAILABLE(&xpm_type, init_xpm_functions);
+#endif
+
+#if defined (HAVE_JPEG) || defined (MAC_OS)
+  if (EQ (type, Qjpeg))
+    return CHECK_LIB_AVAILABLE(&jpeg_type, init_jpeg_functions);
+#endif
+
+#if defined (HAVE_TIFF) || defined (MAC_OS)
+  if (EQ (type, Qtiff))
+    return CHECK_LIB_AVAILABLE(&tiff_type, init_tiff_functions);
+#endif
+
+#if defined (HAVE_GIF) || defined (MAC_OS)
+  if (EQ (type, Qgif))
+    return CHECK_LIB_AVAILABLE(&gif_type, init_gif_functions);
+#endif
+
+#if defined (HAVE_PNG) || defined (MAC_OS)
+  if (EQ (type, Qpng))
+    return CHECK_LIB_AVAILABLE(&png_type, init_png_functions);
+#endif
+
+#ifdef HAVE_GHOSTSCRIPT
+  if (EQ (type, Qpostscript))
+    return CHECK_LIB_AVAILABLE(&gs_type, init_gs_functions);
+#endif
+
+  /* If the type is not recognized, avoid testing it ever again.  */
+  CACHE_IMAGE_TYPE(type, Qnil);
+  return Qnil;
+}
+
 void
 syms_of_image ()
 {
+  /* Must be defined now becase we're going to update it below, while
+     defining the supported image types.  */
+  DEFVAR_LISP ("image-types", &Vimage_types,
+    doc: /* List of potentially supported image types.
+Each element of the list is a symbol for a image type, like 'jpeg or 'png.
+To check whether it is really supported, use `image-type-available-p'.  */);
+  Vimage_types = Qnil;
+
+  Vimage_type_cache = Qnil;
+  staticpro (&Vimage_type_cache);
+
   QCascent = intern (":ascent");
   staticpro (&QCascent);
@@ -7917,4 +8028,5 @@
   staticpro (&Qpostscript);
 #ifdef HAVE_GHOSTSCRIPT
+  ADD_IMAGE_TYPE(Qpostscript);
   QCloader = intern (":loader");
   staticpro (&QCloader);
@@ -7929,11 +8041,14 @@
   Qpbm = intern ("pbm");
   staticpro (&Qpbm);
+  ADD_IMAGE_TYPE(Qpbm);
 
   Qxbm = intern ("xbm");
   staticpro (&Qxbm);
+  ADD_IMAGE_TYPE(Qxbm);
 
 #if defined (HAVE_XPM) || defined (MAC_OS)
   Qxpm = intern ("xpm");
   staticpro (&Qxpm);
+  ADD_IMAGE_TYPE(Qxpm);
 #endif
 
@@ -7941,4 +8056,5 @@
   Qjpeg = intern ("jpeg");
   staticpro (&Qjpeg);
+  ADD_IMAGE_TYPE(Qjpeg);
 #endif
 
@@ -7946,4 +8062,5 @@
   Qtiff = intern ("tiff");
   staticpro (&Qtiff);
+  ADD_IMAGE_TYPE(Qtiff);
 #endif
 
@@ -7951,4 +8068,5 @@
   Qgif = intern ("gif");
   staticpro (&Qgif);
+  ADD_IMAGE_TYPE(Qgif);
 #endif
 
@@ -7956,6 +8074,8 @@
   Qpng = intern ("png");
   staticpro (&Qpng);
+  ADD_IMAGE_TYPE(Qpng);
 #endif
 
+  defsubr (&Sinit_image_library);
   defsubr (&Sclear_image_cache);
   defsubr (&Simage_size);
@@ -7985,50 +8105,11 @@
 }
 
-
-#ifdef HAVE_NTGUI
-/* Image types that rely on external libraries are loaded dynamically
-   if the library is available.  */
-#define IF_LIB_AVAILABLE(init_lib_fn)  if (init_lib_fn())
-#else
-#define IF_LIB_AVAILABLE(init_func)    /* Load unconditionally */
-#endif /* HAVE_NTGUI */
-
 void
 init_image ()
 {
   image_types = NULL;
-  Vimage_types = Qnil;
 
-  define_image_type (&xbm_type);
-  define_image_type (&pbm_type);
-
-#if defined (HAVE_XPM) || defined (MAC_OS)
-  IF_LIB_AVAILABLE(init_xpm_functions)
-    define_image_type (&xpm_type);
-#endif
-
-#if defined (HAVE_JPEG) || defined (MAC_OS)
-  IF_LIB_AVAILABLE(init_jpeg_functions)
-    define_image_type (&jpeg_type);
-#endif
-
-#if defined (HAVE_TIFF) || defined (MAC_OS)
-  IF_LIB_AVAILABLE(init_tiff_functions)
-    define_image_type (&tiff_type);
-#endif
-
-#if defined (HAVE_GIF) || defined (MAC_OS)
-  IF_LIB_AVAILABLE(init_gif_functions)
-    define_image_type (&gif_type);
-#endif
-
-#if defined (HAVE_PNG) || defined (MAC_OS)
-  IF_LIB_AVAILABLE(init_png_functions)
-    define_image_type (&png_type);
-#endif
-
-#ifdef HAVE_GHOSTSCRIPT
-  define_image_type (&gs_type);
-#endif
+  define_image_type (&xbm_type, TRUE);
+  define_image_type (&pbm_type, TRUE);
 
 #ifdef MAC_OS
diff -Bru2 old/src/xdisp.c new/src/xdisp.c
--- old/src/xdisp.c	2004-06-10 09:28:26.000000000 +0200
+++ new/src/xdisp.c	2004-06-10 11:46:41.000000000 +0200
@@ -671,8 +671,4 @@
 Lisp_Object Vhscroll_step;
 
-/* A list of symbols, one for each supported image type.  */
-
-Lisp_Object Vimage_types;
-
 /* The variable `resize-mini-windows'.  If nil, don't resize
    mini-windows.  If t, always resize them to fit the text they
@@ -22260,9 +22256,4 @@
   Vhscroll_step = make_number (0);
 
-  DEFVAR_LISP ("image-types", &Vimage_types,
-    doc: /* List of supported image types.
-Each element of the list is a symbol for a supported image type.  */);
-  Vimage_types = Qnil;
-
   DEFVAR_BOOL ("message-truncate-lines", &message_truncate_lines,
     doc: /* If non-nil, messages are truncated instead of resizing the echo area.