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Introduce a mechanism by which calls to midend_supersede_game_desc()
can trigger a call to a front end notification function. Use this to
update the game ID permalink when Mines supersedes its game ID.

[originally from svn r9793]

--- a/devel.but

+++ b/devel.but

@@ -1609,6 +1609,10 @@

 think again repeatedly in the hope of finding a better way to do

 whatever it was you needed to do.

+If a front end wants to be notified when this happens, it can ask the

+midend to do so by calling \cw{midend_request_desc_changes()}; see

+\k{midend-request-desc-changes}.

+

 \C{drawing} The drawing API

 The back end function \cw{redraw()} (\k{backend-redraw}) is required

@@ -3269,6 +3273,27 @@

 (This isn't strictly speaking a midend function, since it doesn't

 accept or return a pointer to a midend. You'd probably call it just

 \e{before} deciding what kind of midend you wanted to instantiate.)

+

+\H{midend-request-desc-changes} \cw{midend_request_desc_changes()}

+

+\c void midend_request_desc_changes(midend *me,

+\c                                  void (*notify)(void *), void *ctx);

+

+This function is called by the front end to request notification by

+the mid-end when a puzzle supersedes its game description (see

+\k{backend-supersede}). After this function is called, any call to

+\cw{midend_supersede_game_desc()} by the back end will cause the

+mid-end to call \cw{notify(ctx)} after the game description is

+changed.

+

+This is for use by puzzles which want to present the game description

+to the user constantly (e.g. as an HTML hyperlink) instead of only

+showing it when the user explicitly requests it.

+

+This is a function I anticipate few front ends needing to implement,

+so I make it a callback rather than a static function in order to

+relieve most front ends of the need to provide an empty

+implementation.

 \H{frontend-backend} Direct reference to the back end structure by

 the front end

--- a/emcc.c

+++ b/emcc.c

@@ -309,6 +309,15 @@

     sfree(seed);

 }

+/*

+ * Callback from the midend if Mines supersedes its game description,

+ * so we can update the permalinks.

+ */

+static void desc_changed(void *ignored)

+{

+    update_permalinks();

+}

+

 /* ----------------------------------------------------------------------

  * Implementation of the drawing API by calling Javascript canvas

  * drawing functions. (Well, half of it; the other half is on the JS

@@ -760,6 +769,13 @@

                 (unsigned)(0.5 + 255 * colours[i*3+2]));

         colour_strings[i] = dupstr(col);

     }

+

+    /*

+     * Request notification if a puzzle (hopefully only ever Mines)

+     * supersedes its game description, so that we can proactively

+     * update the permalink.

+     */

+    midend_request_desc_changes(me, desc_changed, NULL);

     /*

      * Draw the puzzle's initial state, and set up the permalinks and

--- a/midend.c

+++ b/midend.c

@@ -81,6 +81,9 @@

     int pressed_mouse_button;

     int preferred_tilesize, tilesize, winwidth, winheight;

+

+    void (*game_desc_change_notify_function)(void *);

+    void *game_desc_change_notify_ctx;

 };

 #define ensure(me) do { \

@@ -1079,6 +1082,12 @@

     return me->ourgame->wants_statusbar;

 }

+void midend_request_desc_changes(midend *me, void (*notify)(void *), void *ctx)

+{

+    me->game_desc_change_notify_function = notify;

+    me->game_desc_change_notify_ctx = ctx;

+}

+

 void midend_supersede_game_desc(midend *me, char *desc, char *privdesc)

 {

     sfree(me->desc);

@@ -1085,6 +1094,8 @@

     sfree(me->privdesc);

     me->desc = dupstr(desc);

     me->privdesc = privdesc ? dupstr(privdesc) : NULL;

+    if (me->game_desc_change_notify_function)

+        me->game_desc_change_notify_function(me->game_desc_change_notify_ctx);

 }

 config_item *midend_get_config(midend *me, int which, char **wintitle)

--- a/puzzles.h

+++ b/puzzles.h

@@ -268,6 +268,8 @@

                          void *rctx);

 char *identify_game(char **name, int (*read)(void *ctx, void *buf, int len),

                     void *rctx);

+void midend_request_desc_changes(midend *me, void (*notify)(void *),

+                                 void *ctx);

 /* Printing functions supplied by the mid-end */

 char *midend_print_puzzle(midend *me, document *doc, int with_soln);

 int midend_tilesize(midend *me);