Keep a set of preferences in the midend.

This commit introduces a serialisation format for the user preferences
stored in game_ui, using the keyword identifiers that get_prefs is
required to write into its list of config_item. As a result, the
serialisation format looks enough like an ordinary config file that a
user could write one by hand.

The preferences for the game backend are kept in serialised form in
me->be_prefs. The typical use of this is to apply it to a just-created
game_ui by calling midend_apply_prefs(), which deserialises the prefs
buffer into a list of config_item and passes it to the backend's
set_prefs function, overwriting the preference fields (but no others)
of the game_ui.

This is duly done when creating a new game, when loading a game from a
save file, and also when printing a puzzle. To make the latter work,
document_add_puzzle now takes a game_ui (and keeps ownership of it
afterwards), and passes that to the backend's compute_size and print
functions.

The backend's own get_prefs and set_prefs functions are wrapped by
midend_get_prefs and midend_set_prefs. This is partly as a convenience
(it deals with optionally constructing a game_ui specially to call the
backend with), but mostly so that there will be a convenient place in
the midend to add standard preferences applying across all puzzles.
No cross-puzzle preferences are provided yet.

There are two external interfaces to all this, and in this commit,
neither one is yet called by any frontend:

A new pair of midend functions is exposed to the front end, called
midend_load_prefs and midend_save_prefs. These have a similar API to
midend_serialise and midend_deserialise, taking a read/write function
pointer and a context. So front ends that can already load/save a game
to a file on disk should find it easy to add a similar set of
functions loading/saving user preferences.

Secondly, a new value CFG_PREFS is added to the enumeration of
configuration dialog types, alongside the ones for the Custom game
type, entering a game description and entering a random seed. This
should make it easy for frontends to offer a Preferences dialog,
because it will operate almost exactly like three dialogs they already
handle.

1 files changed, 7 insertions, 2 deletions

diff --git a/puzzles.h b/puzzles.h
index 7e192c0..e429c26 100644
--- a/puzzles.h
+++ b/puzzles.h
@@ -331,7 +331,7 @@ void midend_timer(midend *me, float tplus);
 struct preset_menu *midend_get_presets(midend *me, int *id_limit);
 int midend_which_preset(midend *me);
 bool midend_wants_statusbar(midend *me);
-enum { CFG_SETTINGS, CFG_SEED, CFG_DESC, CFG_FRONTEND_SPECIFIC };
+enum { CFG_SETTINGS, CFG_SEED, CFG_DESC, CFG_PREFS, CFG_FRONTEND_SPECIFIC };
 config_item *midend_get_config(midend *me, int which, char **wintitle);
 const char *midend_set_config(midend *me, int which, config_item *cfg);
 const char *midend_game_id(midend *me, const char *id);
@@ -352,6 +352,11 @@ void midend_serialise(midend *me,
 const char *midend_deserialise(midend *me,
                                bool (*read)(void *ctx, void *buf, int len),
                                void *rctx);
+const char *midend_load_prefs(
+    midend *me, bool (*read)(void *ctx, void *buf, int len), void *rctx);
+void midend_save_prefs(midend *me,
+                       void (*write)(void *ctx, const void *buf, int len),
+                       void *wctx);
 const char *identify_game(char **name,
                           bool (*read)(void *ctx, void *buf, int len),
                           void *rctx);
@@ -557,7 +562,7 @@ void SHA_Simple(const void *p, int len, unsigned char *output);
 document *document_new(int pw, int ph, float userscale);
 void document_free(document *doc);
 void document_add_puzzle(document *doc, const game *game, game_params *par,
-			 game_state *st, game_state *st2);
+			 game_ui *ui, game_state *st, game_state *st2);
 int document_npages(const document *doc);
 void document_begin(const document *doc, drawing *dr);
 void document_end(const document *doc, drawing *dr);