Port of Simon Tatham's Puzzle Collection

Original revision: 5123b1bf68777ffa86e651f178046b26a87cf2d9

MIT Licensed. Some games still crash and others are unplayable due to
issues with controls. Still need a "real" polygon filling algorithm.

Currently builds one plugin per puzzle (about 40 in total, around 100K
each on ARM), but can easily be made to build a single monolithic
overlay (800K or so on ARM).

The following games are at least partially broken for various reasons,
and have been disabled on this commit:

Cube:     failed assertion with "Icosahedron" setting
Keen:     input issues
Mines:    weird stuff happens on target
Palisade: input issues
Solo:     input issues, occasional crash on target
Towers:   input issues
Undead:   input issues
Unequal:  input and drawing issues (concave polys)
Untangle: input issues

Features left to do:
 - In-game help system
 - Figure out the weird bugs

Change-Id: I7c69b6860ab115f973c8d76799502e9bb3d52368

1 files changed, 2136 insertions, 0 deletions

diff --git a/apps/plugins/puzzles/midend.c b/apps/plugins/puzzles/midend.c
new file mode 100644
index 0000000000..e2938a45bc
--- /dev/null
+++ b/apps/plugins/puzzles/midend.c
@@ -0,0 +1,2136 @@
+/*
+ * midend.c: general middle fragment sitting between the
+ * platform-specific front end and game-specific back end.
+ * Maintains a move list, takes care of Undo and Redo commands, and
+ * processes standard keystrokes for undo/redo/new/quit.
+ */
+#include "puzzles.h"
+
+#include "rbcompat.h"
+#include "rbassert.h"
+
+enum { DEF_PARAMS, DEF_SEED, DEF_DESC };   /* for midend_game_id_int */
+
+enum { NEWGAME, MOVE, SOLVE, RESTART };/* for midend_state_entry.movetype */
+
+#define special(type) ( (type) != MOVE )
+
+struct midend_state_entry {
+    game_state *state;
+    char *movestr;
+    int movetype;
+};
+
+struct midend {
+    frontend *frontend;
+    random_state *random;
+    const game *ourgame;
+
+    game_params **presets;
+    char **preset_names, **preset_encodings;
+    int npresets, presetsize;
+
+    /*
+     * `desc' and `privdesc' deserve a comment.
+     * 
+     * `desc' is the game description as presented to the user when
+     * they ask for Game -> Specific. `privdesc', if non-NULL, is a
+     * different game description used to reconstruct the initial
+     * game_state when de-serialising. If privdesc is NULL, `desc'
+     * is used for both.
+     * 
+     * For almost all games, `privdesc' is NULL and never used. The
+     * exception (as usual) is Mines: the initial game state has no
+     * squares open at all, but after the first click `desc' is
+     * rewritten to describe a game state with an initial click and
+     * thus a bunch of squares open. If we used that desc to
+     * serialise and deserialise, then the initial game state after
+     * deserialisation would look unlike the initial game state
+     * beforehand, and worse still execute_move() might fail on the
+     * attempted first click. So `privdesc' is also used in this
+     * case, to provide a game description describing the same
+     * fixed mine layout _but_ no initial click. (These game IDs
+     * may also be typed directly into Mines if you like.)
+     */
+    char *desc, *privdesc, *seedstr;
+    char *aux_info;
+    enum { GOT_SEED, GOT_DESC, GOT_NOTHING } genmode;
+
+    int nstates, statesize, statepos;
+    struct midend_state_entry *states;
+
+    game_params *params, *curparams;
+    game_drawstate *drawstate;
+    game_ui *ui;
+
+    game_state *oldstate;
+    float anim_time, anim_pos;
+    float flash_time, flash_pos;
+    int dir;
+
+    int timing;
+    float elapsed;
+    char *laststatus;
+
+    drawing *drawing;
+
+    int pressed_mouse_button;
+
+    int preferred_tilesize, tilesize, winwidth, winheight;
+
+    void (*game_id_change_notify_function)(void *);
+    void *game_id_change_notify_ctx;
+};
+
+#define ensure(me) do { \
+    if ((me)->nstates >= (me)->statesize) { \
+        (me)->statesize = (me)->nstates + 128; \
+        (me)->states = sresize((me)->states, (me)->statesize, \
+                               struct midend_state_entry); \
+    } \
+} while (0)
+
+void midend_reset_tilesize(midend *me)
+{
+    me->preferred_tilesize = me->ourgame->preferred_tilesize;
+    {
+        /*
+         * Allow an environment-based override for the default tile
+         * size by defining a variable along the lines of
+         * `NET_TILESIZE=15'.
+         */
+
+        char buf[80], *e;
+        int j, k, ts;
+
+        sprintf(buf, "%s_TILESIZE", me->ourgame->name);
+        for (j = k = 0; buf[j]; j++)
+            if (!isspace((unsigned char)buf[j]))
+                buf[k++] = toupper((unsigned char)buf[j]);
+        buf[k] = '\0';
+        if ((e = getenv(buf)) != NULL && sscanf(e, "%d", &ts) == 1 && ts > 0)
+            me->preferred_tilesize = ts;
+    }
+}
+
+midend *midend_new(frontend *fe, const game *ourgame,
+                   const drawing_api *drapi, void *drhandle)
+{
+    midend *me = snew(midend);
+    void *randseed;
+    int randseedsize;
+
+    get_random_seed(&randseed, &randseedsize);
+
+    me->frontend = fe;
+    me->ourgame = ourgame;
+    me->random = random_new(randseed, randseedsize);
+    me->nstates = me->statesize = me->statepos = 0;
+    me->states = NULL;
+    me->params = ourgame->default_params();
+    me->game_id_change_notify_function = NULL;
+    me->game_id_change_notify_ctx = NULL;
+
+    /*
+     * Allow environment-based changing of the default settings by
+     * defining a variable along the lines of `NET_DEFAULT=25x25w'
+     * in which the value is an encoded parameter string.
+     */
+    {
+        char buf[80], *e;
+        int j, k;
+        sprintf(buf, "%s_DEFAULT", me->ourgame->name);
+        for (j = k = 0; buf[j]; j++)
+            if (!isspace((unsigned char)buf[j]))
+                buf[k++] = toupper((unsigned char)buf[j]);
+        buf[k] = '\0';
+        if ((e = getenv(buf)) != NULL)
+            me->ourgame->decode_params(me->params, e);
+    }
+    me->curparams = NULL;
+    me->desc = me->privdesc = NULL;
+    me->seedstr = NULL;
+    me->aux_info = NULL;
+    me->genmode = GOT_NOTHING;
+    me->drawstate = NULL;
+    me->oldstate = NULL;
+    me->presets = NULL;
+    me->preset_names = NULL;
+    me->preset_encodings = NULL;
+    me->npresets = me->presetsize = 0;
+    me->anim_time = me->anim_pos = 0.0F;
+    me->flash_time = me->flash_pos = 0.0F;
+    me->dir = 0;
+    me->ui = NULL;
+    me->pressed_mouse_button = 0;
+    me->laststatus = NULL;
+    me->timing = FALSE;
+    me->elapsed = 0.0F;
+    me->tilesize = me->winwidth = me->winheight = 0;
+    if (drapi)
+        me->drawing = drawing_new(drapi, me, drhandle);
+    else
+        me->drawing = NULL;
+
+    midend_reset_tilesize(me);
+
+    sfree(randseed);
+
+    return me;
+}
+
+const game *midend_which_game(midend *me)
+{
+    return me->ourgame;
+}
+
+static void midend_purge_states(midend *me)
+{
+    while (me->nstates > me->statepos) {
+        me->ourgame->free_game(me->states[--me->nstates].state);
+        if (me->states[me->nstates].movestr)
+            sfree(me->states[me->nstates].movestr);
+    }
+}
+
+static void midend_free_game(midend *me)
+{
+    while (me->nstates > 0) {
+        me->nstates--;
+        me->ourgame->free_game(me->states[me->nstates].state);
+        sfree(me->states[me->nstates].movestr);
+    }
+
+    if (me->drawstate)
+        me->ourgame->free_drawstate(me->drawing, me->drawstate);
+}
+
+void midend_free(midend *me)
+{
+    int i;
+
+    midend_free_game(me);
+
+    if (me->drawing)
+        drawing_free(me->drawing);
+    random_free(me->random);
+    sfree(me->states);
+    sfree(me->desc);
+    sfree(me->privdesc);
+    sfree(me->seedstr);
+    sfree(me->aux_info);
+    me->ourgame->free_params(me->params);
+    if (me->npresets) {
+        for (i = 0; i < me->npresets; i++) {
+            sfree(me->presets[i]);
+            sfree(me->preset_names[i]);
+            sfree(me->preset_encodings[i]);
+        }
+        sfree(me->presets);
+        sfree(me->preset_names);
+        sfree(me->preset_encodings);
+    }
+    if (me->ui)
+        me->ourgame->free_ui(me->ui);
+    if (me->curparams)
+        me->ourgame->free_params(me->curparams);
+    sfree(me->laststatus);
+    sfree(me);
+}
+
+static void midend_size_new_drawstate(midend *me)
+{
+    /*
+     * Don't even bother, if we haven't worked out our tile size
+     * anyway yet.
+     */
+    if (me->tilesize > 0) {
+        me->ourgame->compute_size(me->params, me->tilesize,
+                                  &me->winwidth, &me->winheight);
+        me->ourgame->set_size(me->drawing, me->drawstate,
+                              me->params, me->tilesize);
+    }
+}
+
+void midend_size(midend *me, int *x, int *y, int user_size)
+{
+    int min, max;
+    int rx, ry;
+
+    /*
+     * We can't set the size on the same drawstate twice. So if
+     * we've already sized one drawstate, we must throw it away and
+     * create a new one.
+     */
+    if (me->drawstate && me->tilesize > 0) {
+        me->ourgame->free_drawstate(me->drawing, me->drawstate);
+        me->drawstate = me->ourgame->new_drawstate(me->drawing,
+                                                   me->states[0].state);
+    }
+
+    /*
+     * Find the tile size that best fits within the given space. If
+     * `user_size' is TRUE, we must actually find the _largest_ such
+     * tile size, in order to get as close to the user's explicit
+     * request as possible; otherwise, we bound above at the game's
+     * preferred tile size, so that the game gets what it wants
+     * provided that this doesn't break the constraint from the
+     * front-end (which is likely to be a screen size or similar).
+     */
+    if (user_size) {
+        max = 1;
+        do {
+            max *= 2;
+            me->ourgame->compute_size(me->params, max, &rx, &ry);
+        } while (rx <= *x && ry <= *y);
+    } else
+        max = me->preferred_tilesize + 1;
+    min = 1;
+
+    /*
+     * Now binary-search between min and max. We're looking for a
+     * boundary rather than a value: the point at which tile sizes
+     * stop fitting within the given dimensions. Thus, we stop when
+     * max and min differ by exactly 1.
+     */
+    while (max - min > 1) {
+        int mid = (max + min) / 2;
+        me->ourgame->compute_size(me->params, mid, &rx, &ry);
+        if (rx <= *x && ry <= *y)
+            min = mid;
+        else
+            max = mid;
+    }
+
+    /*
+     * Now `min' is a valid size, and `max' isn't. So use `min'.
+     */
+
+    me->tilesize = min;
+    if (user_size)
+        /* If the user requested a change in size, make it permanent. */
+        me->preferred_tilesize = me->tilesize;
+    midend_size_new_drawstate(me);
+    *x = me->winwidth;
+    *y = me->winheight;
+}
+
+int midend_tilesize(midend *me) { return me->tilesize; }
+
+void midend_set_params(midend *me, game_params *params)
+{
+    me->ourgame->free_params(me->params);
+    me->params = me->ourgame->dup_params(params);
+}
+
+game_params *midend_get_params(midend *me)
+{
+    return me->ourgame->dup_params(me->params);
+}
+
+static void midend_set_timer(midend *me)
+{
+    me->timing = (me->ourgame->is_timed &&
+                  me->ourgame->timing_state(me->states[me->statepos-1].state,
+                                            me->ui));
+    if (me->timing || me->flash_time || me->anim_time)
+        activate_timer(me->frontend);
+    else
+        deactivate_timer(me->frontend);
+}
+
+void midend_force_redraw(midend *me)
+{
+    if (me->drawstate)
+        me->ourgame->free_drawstate(me->drawing, me->drawstate);
+    me->drawstate = me->ourgame->new_drawstate(me->drawing,
+                                               me->states[0].state);
+    midend_size_new_drawstate(me);
+    midend_redraw(me);
+}
+
+void midend_new_game(midend *me)
+{
+    midend_stop_anim(me);
+    midend_free_game(me);
+
+    assert(me->nstates == 0);
+
+    if (me->genmode == GOT_DESC) {
+        me->genmode = GOT_NOTHING;
+    } else {
+        random_state *rs;
+
+        if (me->genmode == GOT_SEED) {
+            me->genmode = GOT_NOTHING;
+        } else {
+            /*
+             * Generate a new random seed. 15 digits comes to about
+             * 48 bits, which should be more than enough.
+             * 
+             * I'll avoid putting a leading zero on the number,
+             * just in case it confuses anybody who thinks it's
+             * processed as an integer rather than a string.
+             */
+            char newseed[16];
+            int i;
+            newseed[15] = '\0';
+            newseed[0] = '1' + (char)random_upto(me->random, 9);
+            for (i = 1; i < 15; i++)
+                newseed[i] = '0' + (char)random_upto(me->random, 10);
+            sfree(me->seedstr);
+            me->seedstr = dupstr(newseed);
+
+            if (me->curparams)
+                me->ourgame->free_params(me->curparams);
+            me->curparams = me->ourgame->dup_params(me->params);
+        }
+
+        sfree(me->desc);
+        sfree(me->privdesc);
+        sfree(me->aux_info);
+        me->aux_info = NULL;
+
+        rs = random_new(me->seedstr, strlen(me->seedstr));
+        /*
+         * If this midend has been instantiated without providing a
+         * drawing API, it is non-interactive. This means that it's
+         * being used for bulk game generation, and hence we should
+         * pass the non-interactive flag to new_desc.
+         */
+        me->desc = me->ourgame->new_desc(me->curparams, rs,
+                                         &me->aux_info, (me->drawing != NULL));
+        me->privdesc = NULL;
+        random_free(rs);
+    }
+
+    ensure(me);
+
+    /*
+     * It might seem a bit odd that we're using me->params to
+     * create the initial game state, rather than me->curparams
+     * which is better tailored to this specific game and which we
+     * always know.
+     * 
+     * It's supposed to be an invariant in the midend that
+     * me->params and me->curparams differ in no aspect that is
+     * important after generation (i.e. after new_desc()). By
+     * deliberately passing the _less_ specific of these two
+     * parameter sets, we provoke play-time misbehaviour in the
+     * case where a game has failed to encode a play-time parameter
+     * in the non-full version of encode_params().
+     */
+    me->states[me->nstates].state =
+        me->ourgame->new_game(me, me->params, me->desc);
+
+    /*
+     * As part of our commitment to self-testing, test the aux
+     * string to make sure nothing ghastly went wrong.
+     */
+    if (me->ourgame->can_solve && me->aux_info) {
+        game_state *s;
+        char *msg, *movestr;
+
+        msg = NULL;
+        movestr = me->ourgame->solve(me->states[0].state,
+                                     me->states[0].state,
+                                     me->aux_info, &msg);
+        assert(movestr && !msg);
+        s = me->ourgame->execute_move(me->states[0].state, movestr);
+        assert(s);
+        me->ourgame->free_game(s);
+        sfree(movestr);
+    }
+
+    me->states[me->nstates].movestr = NULL;
+    me->states[me->nstates].movetype = NEWGAME;
+    me->nstates++;
+    me->statepos = 1;
+    me->drawstate = me->ourgame->new_drawstate(me->drawing,
+                                               me->states[0].state);
+    midend_size_new_drawstate(me);
+    me->elapsed = 0.0F;
+    me->flash_pos = me->flash_time = 0.0F;
+    me->anim_pos = me->anim_time = 0.0F;
+    if (me->ui)
+        me->ourgame->free_ui(me->ui);
+    me->ui = me->ourgame->new_ui(me->states[0].state);
+    midend_set_timer(me);
+    me->pressed_mouse_button = 0;
+
+    if (me->game_id_change_notify_function)
+        me->game_id_change_notify_function(me->game_id_change_notify_ctx);
+}
+
+int midend_can_undo(midend *me)
+{
+    return (me->statepos > 1);
+}
+
+int midend_can_redo(midend *me)
+{
+    return (me->statepos < me->nstates);
+}
+
+static int midend_undo(midend *me)
+{
+    if (me->statepos > 1) {
+        if (me->ui)
+            me->ourgame->changed_state(me->ui,
+                                       me->states[me->statepos-1].state,
+                                       me->states[me->statepos-2].state);
+        me->statepos--;
+        me->dir = -1;
+        return 1;
+    } else
+        return 0;
+}
+
+static int midend_redo(midend *me)
+{
+    if (me->statepos < me->nstates) {
+        if (me->ui)
+            me->ourgame->changed_state(me->ui,
+                                       me->states[me->statepos-1].state,
+                                       me->states[me->statepos].state);
+        me->statepos++;
+        me->dir = +1;
+        return 1;
+    } else
+        return 0;
+}
+
+static void midend_finish_move(midend *me)
+{
+    float flashtime;
+
+    /*
+     * We do not flash if the later of the two states is special.
+     * This covers both forward Solve moves and backward (undone)
+     * Restart moves.
+     */
+    if ((me->oldstate || me->statepos > 1) &&
+        ((me->dir > 0 && !special(me->states[me->statepos-1].movetype)) ||
+         (me->dir < 0 && me->statepos < me->nstates &&
+          !special(me->states[me->statepos].movetype)))) {
+        flashtime = me->ourgame->flash_length(me->oldstate ? me->oldstate :
+                                              me->states[me->statepos-2].state,
+                                              me->states[me->statepos-1].state,
+                                              me->oldstate ? me->dir : +1,
+                                              me->ui);
+        if (flashtime > 0) {
+            me->flash_pos = 0.0F;
+            me->flash_time = flashtime;
+        }
+    }
+
+    if (me->oldstate)
+        me->ourgame->free_game(me->oldstate);
+    me->oldstate = NULL;
+    me->anim_pos = me->anim_time = 0;
+    me->dir = 0;
+
+    midend_set_timer(me);
+}
+
+void midend_stop_anim(midend *me)
+{
+    if (me->oldstate || me->anim_time != 0) {
+        midend_finish_move(me);
+        midend_redraw(me);
+    }
+}
+
+void midend_restart_game(midend *me)
+{
+    game_state *s;
+
+    assert(me->statepos >= 1);
+    if (me->statepos == 1)
+        return;                        /* no point doing anything at all! */
+
+    /*
+     * During restart, we reconstruct the game from the (public)
+     * game description rather than from states[0], because that
+     * way Mines gets slightly more sensible behaviour (restart
+     * goes to _after_ the first click so you don't have to
+     * remember where you clicked).
+     */
+    s = me->ourgame->new_game(me, me->params, me->desc);
+
+    /*
+     * Now enter the restarted state as the next move.
+     */
+    midend_stop_anim(me);
+    midend_purge_states(me);
+    ensure(me);
+    me->states[me->nstates].state = s;
+    me->states[me->nstates].movestr = dupstr(me->desc);
+    me->states[me->nstates].movetype = RESTART;
+    me->statepos = ++me->nstates;
+    if (me->ui)
+        me->ourgame->changed_state(me->ui,
+                                   me->states[me->statepos-2].state,
+                                   me->states[me->statepos-1].state);
+    me->flash_pos = me->flash_time = 0.0F;
+    midend_finish_move(me);
+    midend_redraw(me);
+    midend_set_timer(me);
+}
+
+static int midend_really_process_key(midend *me, int x, int y, int button)
+{
+    game_state *oldstate =
+        me->ourgame->dup_game(me->states[me->statepos - 1].state);
+    int type = MOVE, gottype = FALSE, ret = 1;
+    float anim_time;
+    game_state *s;
+    char *movestr;
+        
+    movestr =
+        me->ourgame->interpret_move(me->states[me->statepos-1].state,
+                                    me->ui, me->drawstate, x, y, button);
+
+    if (!movestr) {
+        if (button == 'n' || button == 'N' || button == '\x0E') {
+            midend_new_game(me);
+            midend_redraw(me);
+            goto done;                 /* never animate */
+        } else if (button == 'u' || button == 'U' ||
+                   button == '\x1A' || button == '\x1F') {
+            midend_stop_anim(me);
+            type = me->states[me->statepos-1].movetype;
+            gottype = TRUE;
+            if (!midend_undo(me))
+                goto done;
+        } else if (button == 'r' || button == 'R' ||
+                   button == '\x12' || button == '\x19') {
+            midend_stop_anim(me);
+            if (!midend_redo(me))
+                goto done;
+        } else if (button == '\x13' && me->ourgame->can_solve) {
+            if (midend_solve(me))
+                goto done;
+        } else if (button == 'q' || button == 'Q' || button == '\x11') {
+            ret = 0;
+            goto done;
+        } else
+            goto done;
+    } else {
+        if (!*movestr)
+            s = me->states[me->statepos-1].state;
+        else {
+            s = me->ourgame->execute_move(me->states[me->statepos-1].state,
+                                          movestr);
+            assert(s != NULL);
+        }
+
+        if (s == me->states[me->statepos-1].state) {
+            /*
+             * make_move() is allowed to return its input state to
+             * indicate that although no move has been made, the UI
+             * state has been updated and a redraw is called for.
+             */
+            midend_redraw(me);
+            midend_set_timer(me);
+            goto done;
+        } else if (s) {
+            midend_stop_anim(me);
+            midend_purge_states(me);
+            ensure(me);
+            assert(movestr != NULL);
+            me->states[me->nstates].state = s;
+            me->states[me->nstates].movestr = movestr;
+            me->states[me->nstates].movetype = MOVE;
+            me->statepos = ++me->nstates;
+            me->dir = +1;
+            if (me->ui)
+                me->ourgame->changed_state(me->ui,
+                                           me->states[me->statepos-2].state,
+                                           me->states[me->statepos-1].state);
+        } else {
+            goto done;
+        }
+    }
+
+    if (!gottype)
+        type = me->states[me->statepos-1].movetype;
+
+    /*
+     * See if this move requires an animation.
+     */
+    if (special(type) && !(type == SOLVE &&
+                           (me->ourgame->flags & SOLVE_ANIMATES))) {
+        anim_time = 0;
+    } else {
+        anim_time = me->ourgame->anim_length(oldstate,
+                                             me->states[me->statepos-1].state,
+                                             me->dir, me->ui);
+    }
+
+    me->oldstate = oldstate; oldstate = NULL;
+    if (anim_time > 0) {
+        me->anim_time = anim_time;
+    } else {
+        me->anim_time = 0.0;
+        midend_finish_move(me);
+    }
+    me->anim_pos = 0.0;
+
+    midend_redraw(me);
+
+    midend_set_timer(me);
+
+    done:
+    if (oldstate) me->ourgame->free_game(oldstate);
+    return ret;
+}
+
+int midend_process_key(midend *me, int x, int y, int button)
+{
+    int ret = 1;
+
+    /*
+     * Harmonise mouse drag and release messages.
+     * 
+     * Some front ends might accidentally switch from sending, say,
+     * RIGHT_DRAG messages to sending LEFT_DRAG, half way through a
+     * drag. (This can happen on the Mac, for example, since
+     * RIGHT_DRAG is usually done using Command+drag, and if the
+     * user accidentally releases Command half way through the drag
+     * then there will be trouble.)
+     * 
+     * It would be an O(number of front ends) annoyance to fix this
+     * in the front ends, but an O(number of back ends) annoyance
+     * to have each game capable of dealing with it. Therefore, we
+     * fix it _here_ in the common midend code so that it only has
+     * to be done once.
+     * 
+     * The possible ways in which things can go screwy in the front
+     * end are:
+     * 
+     *  - in a system containing multiple physical buttons button
+     *    presses can inadvertently overlap. We can see ABab (caps
+     *    meaning button-down and lowercase meaning button-up) when
+     *    the user had semantically intended AaBb.
+     * 
+     *  - in a system where one button is simulated by means of a
+     *    modifier key and another button, buttons can mutate
+     *    between press and release (possibly during drag). So we
+     *    can see Ab instead of Aa.
+     * 
+     * Definite requirements are:
+     * 
+     *  - button _presses_ must never be invented or destroyed. If
+     *    the user presses two buttons in succession, the button
+     *    presses must be transferred to the backend unchanged. So
+     *    if we see AaBb , that's fine; if we see ABab (the button
+     *    presses inadvertently overlapped) we must somehow
+     *    `correct' it to AaBb.
+     * 
+     *  - every mouse action must end up looking like a press, zero
+     *    or more drags, then a release. This allows back ends to
+     *    make the _assumption_ that incoming mouse data will be
+     *    sane in this regard, and not worry about the details.
+     * 
+     * So my policy will be:
+     * 
+     *  - treat any button-up as a button-up for the currently
+     *    pressed button, or ignore it if there is no currently
+     *    pressed button.
+     * 
+     *  - treat any drag as a drag for the currently pressed
+     *    button, or ignore it if there is no currently pressed
+     *    button.
+     * 
+     *  - if we see a button-down while another button is currently
+     *    pressed, invent a button-up for the first one and then
+     *    pass the button-down through as before.
+     * 
+     * 2005-05-31: An addendum to the above. Some games might want
+     * a `priority order' among buttons, such that if one button is
+     * pressed while another is down then a fixed one of the
+     * buttons takes priority no matter what order they're pressed
+     * in. Mines, in particular, wants to treat a left+right click
+     * like a left click for the benefit of users of other
+     * implementations. So the last of the above points is modified
+     * in the presence of an (optional) button priority order.
+     *
+     * A further addition: we translate certain keyboard presses to
+     * cursor key 'select' buttons, so that a) frontends don't have
+     * to translate these themselves (like they do for CURSOR_UP etc),
+     * and b) individual games don't have to hard-code button presses
+     * of '\n' etc for keyboard-based cursors. The choice of buttons
+     * here could eventually be controlled by a runtime configuration
+     * option.
+     */
+    if (IS_MOUSE_DRAG(button) || IS_MOUSE_RELEASE(button)) {
+        if (me->pressed_mouse_button) {
+            if (IS_MOUSE_DRAG(button)) {
+                button = me->pressed_mouse_button +
+                    (LEFT_DRAG - LEFT_BUTTON);
+            } else {
+                button = me->pressed_mouse_button +
+                    (LEFT_RELEASE - LEFT_BUTTON);
+            }
+        } else
+            return ret;                /* ignore it */
+    } else if (IS_MOUSE_DOWN(button) && me->pressed_mouse_button) {
+        /*
+         * If the new button has lower priority than the old one,
+         * don't bother doing this.
+         */
+        if (me->ourgame->flags &
+            BUTTON_BEATS(me->pressed_mouse_button, button))
+            return ret;                /* just ignore it */
+
+        /*
+         * Fabricate a button-up for the previously pressed button.
+         */
+        ret = ret && midend_really_process_key
+            (me, x, y, (me->pressed_mouse_button +
+                        (LEFT_RELEASE - LEFT_BUTTON)));
+    }
+
+    /*
+     * Translate keyboard presses to cursor selection.
+     */
+    if (button == '\n' || button == '\r')
+      button = CURSOR_SELECT;
+    if (button == ' ')
+      button = CURSOR_SELECT2;
+
+    /*
+     * Normalise both backspace characters (8 and 127) to \b. Easier
+     * to do this once, here, than to require all front ends to
+     * carefully generate the same one - now each front end can
+     * generate whichever is easiest.
+     */
+    if (button == '\177')
+        button = '\b';
+
+    /*
+     * Now send on the event we originally received.
+     */
+    ret = ret && midend_really_process_key(me, x, y, button);
+
+    /*
+     * And update the currently pressed button.
+     */
+    if (IS_MOUSE_RELEASE(button))
+        me->pressed_mouse_button = 0;
+    else if (IS_MOUSE_DOWN(button))
+        me->pressed_mouse_button = button;
+
+    return ret;
+}
+
+void midend_redraw(midend *me)
+{
+    assert(me->drawing);
+
+    if (me->statepos > 0 && me->drawstate) {
+        start_draw(me->drawing);
+        if (me->oldstate && me->anim_time > 0 &&
+            me->anim_pos < me->anim_time) {
+            assert(me->dir != 0);
+            me->ourgame->redraw(me->drawing, me->drawstate, me->oldstate,
+                                me->states[me->statepos-1].state, me->dir,
+                                me->ui, me->anim_pos, me->flash_pos);
+        } else {
+            me->ourgame->redraw(me->drawing, me->drawstate, NULL,
+                                me->states[me->statepos-1].state, +1 /*shrug*/,
+                                me->ui, 0.0, me->flash_pos);
+        }
+        end_draw(me->drawing);
+    }
+}
+
+/*
+ * Nasty hacky function used to implement the --redo option in
+ * gtk.c. Only used for generating the puzzles' icons.
+ */
+void midend_freeze_timer(midend *me, float tprop)
+{
+    me->anim_pos = me->anim_time * tprop;
+    midend_redraw(me);
+    deactivate_timer(me->frontend);
+}
+
+void midend_timer(midend *me, float tplus)
+{
+    int need_redraw = (me->anim_time > 0 || me->flash_time > 0);
+
+    me->anim_pos += tplus;
+    if (me->anim_pos >= me->anim_time ||
+        me->anim_time == 0 || !me->oldstate) {
+        if (me->anim_time > 0)
+            midend_finish_move(me);
+    }
+
+    me->flash_pos += tplus;
+    if (me->flash_pos >= me->flash_time || me->flash_time == 0) {
+        me->flash_pos = me->flash_time = 0;
+    }
+
+    if (need_redraw)
+        midend_redraw(me);
+
+    if (me->timing) {
+        float oldelapsed = me->elapsed;
+        me->elapsed += tplus;
+        if ((int)oldelapsed != (int)me->elapsed)
+            status_bar(me->drawing, me->laststatus ? me->laststatus : "");
+    }
+
+    midend_set_timer(me);
+}
+
+float *midend_colours(midend *me, int *ncolours)
+{
+    float *ret;
+
+    ret = me->ourgame->colours(me->frontend, ncolours);
+
+    {
+        int i;
+
+        /*
+         * Allow environment-based overrides for the standard
+         * colours by defining variables along the lines of
+         * `NET_COLOUR_4=6000c0'.
+         */
+
+        for (i = 0; i < *ncolours; i++) {
+            char buf[80], *e;
+            unsigned int r, g, b;
+            int j, k;
+
+            sprintf(buf, "%s_COLOUR_%d", me->ourgame->name, i);
+            for (j = k = 0; buf[j]; j++)
+                if (!isspace((unsigned char)buf[j]))
+                    buf[k++] = toupper((unsigned char)buf[j]);
+            buf[k] = '\0';
+            if ((e = getenv(buf)) != NULL &&
+                sscanf(e, "%2x%2x%2x", &r, &g, &b) == 3) {
+                ret[i*3 + 0] = r / 255.0F;
+                ret[i*3 + 1] = g / 255.0F;
+                ret[i*3 + 2] = b / 255.0F;
+            }
+        }
+    }
+
+    return ret;
+}
+
+int midend_num_presets(midend *me)
+{
+    if (!me->npresets) {
+        char *name;
+        game_params *preset;
+
+        while (me->ourgame->fetch_preset(me->npresets, &name, &preset)) {
+            if (me->presetsize <= me->npresets) {
+                me->presetsize = me->npresets + 10;
+                me->presets = sresize(me->presets, me->presetsize,
+                                      game_params *);
+                me->preset_names = sresize(me->preset_names, me->presetsize,
+                                           char *);
+                me->preset_encodings = sresize(me->preset_encodings,
+                                               me->presetsize, char *);
+            }
+
+            me->presets[me->npresets] = preset;
+            me->preset_names[me->npresets] = name;
+            me->preset_encodings[me->npresets] =
+                me->ourgame->encode_params(preset, TRUE);;
+            me->npresets++;
+        }
+    }
+
+    {
+        /*
+         * Allow environment-based extensions to the preset list by
+         * defining a variable along the lines of `SOLO_PRESETS=2x3
+         * Advanced:2x3da'. Colon-separated list of items,
+         * alternating between textual titles in the menu and
+         * encoded parameter strings.
+         */
+        char buf[80], *e, *p;
+        int j, k;
+
+        sprintf(buf, "%s_PRESETS", me->ourgame->name);
+        for (j = k = 0; buf[j]; j++)
+            if (!isspace((unsigned char)buf[j]))
+                buf[k++] = toupper((unsigned char)buf[j]);
+        buf[k] = '\0';
+
+        if ((e = getenv(buf)) != NULL) {
+            p = e = dupstr(e);
+
+            while (*p) {
+                char *name, *val;
+                game_params *preset;
+
+                name = p;
+                while (*p && *p != ':') p++;
+                if (*p) *p++ = '\0';
+                val = p;
+                while (*p && *p != ':') p++;
+                if (*p) *p++ = '\0';
+
+                preset = me->ourgame->default_params();
+                me->ourgame->decode_params(preset, val);
+
+                if (me->ourgame->validate_params(preset, TRUE)) {
+                    /* Drop this one from the list. */
+                    me->ourgame->free_params(preset);
+                    continue;
+                }
+
+                if (me->presetsize <= me->npresets) {
+                    me->presetsize = me->npresets + 10;
+                    me->presets = sresize(me->presets, me->presetsize,
+                                          game_params *);
+                    me->preset_names = sresize(me->preset_names,
+                                               me->presetsize, char *);
+                    me->preset_encodings = sresize(me->preset_encodings,
+                                                   me->presetsize, char *);
+                }
+
+                me->presets[me->npresets] = preset;
+                me->preset_names[me->npresets] = dupstr(name);
+                me->preset_encodings[me->npresets] =
+                    me->ourgame->encode_params(preset, TRUE);
+                me->npresets++;
+            }
+            sfree(e);
+        }
+    }
+
+    return me->npresets;
+}
+
+void midend_fetch_preset(midend *me, int n,
+                         char **name, game_params **params)
+{
+    assert(n >= 0 && n < me->npresets);
+    *name = me->preset_names[n];
+    *params = me->presets[n];
+}
+
+int midend_which_preset(midend *me)
+{
+    char *encoding = me->ourgame->encode_params(me->params, TRUE);
+    int i, ret;
+
+    ret = -1;
+    for (i = 0; i < me->npresets; i++)
+        if (!strcmp(encoding, me->preset_encodings[i])) {
+            ret = i;
+            break;
+        }
+
+    sfree(encoding);
+    return ret;
+}
+
+int midend_wants_statusbar(midend *me)
+{
+    return me->ourgame->wants_statusbar;
+}
+
+void midend_request_id_changes(midend *me, void (*notify)(void *), void *ctx)
+{
+    me->game_id_change_notify_function = notify;
+    me->game_id_change_notify_ctx = ctx;
+}
+
+void midend_supersede_game_desc(midend *me, char *desc, char *privdesc)
+{
+    sfree(me->desc);
+    sfree(me->privdesc);
+    me->desc = dupstr(desc);
+    me->privdesc = privdesc ? dupstr(privdesc) : NULL;
+    if (me->game_id_change_notify_function)
+        me->game_id_change_notify_function(me->game_id_change_notify_ctx);
+}
+
+config_item *midend_get_config(midend *me, int which, char **wintitle)
+{
+    char *titlebuf, *parstr, *rest;
+    config_item *ret;
+    char sep;
+
+    assert(wintitle);
+    titlebuf = snewn(40 + strlen(me->ourgame->name), char);
+
+    switch (which) {
+      case CFG_SETTINGS:
+        sprintf(titlebuf, "%s configuration", me->ourgame->name);
+        *wintitle = titlebuf;
+        return me->ourgame->configure(me->params);
+      case CFG_SEED:
+      case CFG_DESC:
+        if (!me->curparams) {
+          sfree(titlebuf);
+          return NULL;
+        }
+        sprintf(titlebuf, "%s %s selection", me->ourgame->name,
+                which == CFG_SEED ? "random" : "game");
+        *wintitle = titlebuf;
+
+        ret = snewn(2, config_item);
+
+        ret[0].type = C_STRING;
+        if (which == CFG_SEED)
+            ret[0].name = "Game random seed";
+        else
+            ret[0].name = "Game ID";
+        ret[0].ival = 0;
+        /*
+         * For CFG_DESC the text going in here will be a string
+         * encoding of the restricted parameters, plus a colon,
+         * plus the game description. For CFG_SEED it will be the
+         * full parameters, plus a hash, plus the random seed data.
+         * Either of these is a valid full game ID (although only
+         * the former is likely to persist across many code
+         * changes).
+         */
+        parstr = me->ourgame->encode_params(me->curparams, which == CFG_SEED);
+        assert(parstr);
+        if (which == CFG_DESC) {
+            rest = me->desc ? me->desc : "";
+            sep = ':';
+        } else {
+            rest = me->seedstr ? me->seedstr : "";
+            sep = '#';
+        }
+        ret[0].sval = snewn(strlen(parstr) + strlen(rest) + 2, char);
+        sprintf(ret[0].sval, "%s%c%s", parstr, sep, rest);
+        sfree(parstr);
+
+        ret[1].type = C_END;
+        ret[1].name = ret[1].sval = NULL;
+        ret[1].ival = 0;
+
+        return ret;
+    }
+
+    assert(!"We shouldn't be here");
+    return NULL;
+}
+
+static char *midend_game_id_int(midend *me, char *id, int defmode)
+{
+    char *error, *par, *desc, *seed;
+    game_params *newcurparams, *newparams, *oldparams1, *oldparams2;
+    int free_params;
+
+    seed = strchr(id, '#');
+    desc = strchr(id, ':');
+
+    if (desc && (!seed || desc < seed)) {
+        /*
+         * We have a colon separating parameters from game
+         * description. So `par' now points to the parameters
+         * string, and `desc' to the description string.
+         */
+        *desc++ = '\0';
+        par = id;
+        seed = NULL;
+    } else if (seed && (!desc || seed < desc)) {
+        /*
+         * We have a hash separating parameters from random seed.
+         * So `par' now points to the parameters string, and `seed'
+         * to the seed string.
+         */
+        *seed++ = '\0';
+        par = id;
+        desc = NULL;
+    } else {
+        /*
+         * We only have one string. Depending on `defmode', we take
+         * it to be either parameters, seed or description.
+         */
+        if (defmode == DEF_SEED) {
+            seed = id;
+            par = desc = NULL;
+        } else if (defmode == DEF_DESC) {
+            desc = id;
+            par = seed = NULL;
+        } else {
+            par = id;
+            seed = desc = NULL;
+        }
+    }
+
+    /*
+     * We must be reasonably careful here not to modify anything in
+     * `me' until we have finished validating things. This function
+     * must either return an error and do nothing to the midend, or
+     * return success and do everything; nothing in between is
+     * acceptable.
+     */
+    newcurparams = newparams = oldparams1 = oldparams2 = NULL;
+
+    if (par) {
+        /*
+         * The params string may underspecify the game parameters, so
+         * we must first initialise newcurparams with a full set of
+         * params from somewhere else before we decode_params the
+         * input string over the top.
+         *
+         * But which set? It depends on what other data we have.
+         *
+         * If we've been given a _descriptive_ game id, then that may
+         * well underspecify by design, e.g. Solo game descriptions
+         * often start just '3x3:' without specifying one of Solo's
+         * difficulty settings, because it isn't necessary once a game
+         * has been generated (and you might not even know it, if
+         * you're manually transcribing a game description). In that
+         * situation, I've always felt that the best thing to set the
+         * difficulty to (for use if the user hits 'New Game' after
+         * pasting in that game id) is whatever it was previously set
+         * to. That is, we use whatever is already in me->params as
+         * the basis for our decoding of this input string.
+         *
+         * A random-seed based game id, however, should use the real,
+         * built-in default params, and not even check the
+         * <game>_DEFAULT environment setting, because when people
+         * paste each other random seeds - whether it's two users
+         * arranging to generate the same game at the same time to
+         * race solving them, or a user sending a bug report upstream
+         * - the whole point is for the random game id to always be
+         * interpreted the same way, even if it does underspecify.
+         *
+         * A parameter string typed in on its own, with no seed _or_
+         * description, gets treated the same way as a random seed,
+         * because again I think the most likely reason for doing that
+         * is to have a portable representation of a set of params.
+         */
+        if (desc) {
+            newcurparams = me->ourgame->dup_params(me->params);
+        } else {
+            newcurparams = me->ourgame->default_params();
+        }
+        me->ourgame->decode_params(newcurparams, par);
+        error = me->ourgame->validate_params(newcurparams, desc == NULL);
+        if (error) {
+            me->ourgame->free_params(newcurparams);
+            return error;
+        }
+        oldparams1 = me->curparams;
+
+        /*
+         * Now filter only the persistent parts of this state into
+         * the long-term params structure, unless we've _only_
+         * received a params string in which case the whole lot is
+         * persistent.
+         */
+        oldparams2 = me->params;
+        if (seed || desc) {
+            char *tmpstr;
+
+            newparams = me->ourgame->dup_params(me->params);
+
+            tmpstr = me->ourgame->encode_params(newcurparams, FALSE);
+            me->ourgame->decode_params(newparams, tmpstr);
+
+            sfree(tmpstr);
+        } else {
+            newparams = me->ourgame->dup_params(newcurparams);
+        }
+        free_params = TRUE;
+    } else {
+        newcurparams = me->curparams;
+        newparams = me->params;
+        free_params = FALSE;
+    }
+
+    if (desc) {
+        error = me->ourgame->validate_desc(newparams, desc);
+        if (error) {
+            if (free_params) {
+                if (newcurparams)
+                    me->ourgame->free_params(newcurparams);
+                if (newparams)
+                    me->ourgame->free_params(newparams);
+            }
+            return error;
+        }
+    }
+
+    /*
+     * Now we've got past all possible error points. Update the
+     * midend itself.
+     */
+    me->params = newparams;
+    me->curparams = newcurparams;
+    if (oldparams1)
+        me->ourgame->free_params(oldparams1);
+    if (oldparams2)
+        me->ourgame->free_params(oldparams2);
+
+    sfree(me->desc);
+    sfree(me->privdesc);
+    me->desc = me->privdesc = NULL;
+    sfree(me->seedstr);
+    me->seedstr = NULL;
+
+    if (desc) {
+        me->desc = dupstr(desc);
+        me->genmode = GOT_DESC;
+        sfree(me->aux_info);
+        me->aux_info = NULL;
+    }
+
+    if (seed) {
+        me->seedstr = dupstr(seed);
+        me->genmode = GOT_SEED;
+    }
+
+    return NULL;
+}
+
+char *midend_game_id(midend *me, char *id)
+{
+    return midend_game_id_int(me, id, DEF_PARAMS);
+}
+
+char *midend_get_game_id(midend *me)
+{
+    char *parstr, *ret;
+
+    parstr = me->ourgame->encode_params(me->curparams, FALSE);
+    assert(parstr);
+    assert(me->desc);
+    ret = snewn(strlen(parstr) + strlen(me->desc) + 2, char);
+    sprintf(ret, "%s:%s", parstr, me->desc);
+    sfree(parstr);
+    return ret;
+}
+
+char *midend_get_random_seed(midend *me)
+{
+    char *parstr, *ret;
+
+    if (!me->seedstr)
+        return NULL;
+
+    parstr = me->ourgame->encode_params(me->curparams, TRUE);
+    assert(parstr);
+    ret = snewn(strlen(parstr) + strlen(me->seedstr) + 2, char);
+    sprintf(ret, "%s#%s", parstr, me->seedstr);
+    sfree(parstr);
+    return ret;
+}
+
+char *midend_set_config(midend *me, int which, config_item *cfg)
+{
+    char *error;
+    game_params *params;
+
+    switch (which) {
+      case CFG_SETTINGS:
+        params = me->ourgame->custom_params(cfg);
+        error = me->ourgame->validate_params(params, TRUE);
+
+        if (error) {
+            me->ourgame->free_params(params);
+            return error;
+        }
+
+        me->ourgame->free_params(me->params);
+        me->params = params;
+        break;
+
+      case CFG_SEED:
+      case CFG_DESC:
+        error = midend_game_id_int(me, cfg[0].sval,
+                                   (which == CFG_SEED ? DEF_SEED : DEF_DESC));
+        if (error)
+            return error;
+        break;
+    }
+
+    return NULL;
+}
+
+int midend_can_format_as_text_now(midend *me)
+{
+    if (me->ourgame->can_format_as_text_ever)
+        return me->ourgame->can_format_as_text_now(me->params);
+    else
+        return FALSE;
+}
+
+char *midend_text_format(midend *me)
+{
+    if (me->ourgame->can_format_as_text_ever && me->statepos > 0 &&
+        me->ourgame->can_format_as_text_now(me->params))
+        return me->ourgame->text_format(me->states[me->statepos-1].state);
+    else
+        return NULL;
+}
+
+char *midend_solve(midend *me)
+{
+    game_state *s;
+    char *msg, *movestr;
+
+    if (!me->ourgame->can_solve)
+        return "This game does not support the Solve operation";
+
+    if (me->statepos < 1)
+        return "No game set up to solve";   /* _shouldn't_ happen! */
+
+    msg = NULL;
+    movestr = me->ourgame->solve(me->states[0].state,
+                                 me->states[me->statepos-1].state,
+                                 me->aux_info, &msg);
+    if (!movestr) {
+        if (!msg)
+            msg = "Solve operation failed";   /* _shouldn't_ happen, but can */
+        return msg;
+    }
+    s = me->ourgame->execute_move(me->states[me->statepos-1].state, movestr);
+    assert(s);
+
+    /*
+     * Now enter the solved state as the next move.
+     */
+    midend_stop_anim(me);
+    midend_purge_states(me);
+    ensure(me);
+    me->states[me->nstates].state = s;
+    me->states[me->nstates].movestr = movestr;
+    me->states[me->nstates].movetype = SOLVE;
+    me->statepos = ++me->nstates;
+    if (me->ui)
+        me->ourgame->changed_state(me->ui,
+                                   me->states[me->statepos-2].state,
+                                   me->states[me->statepos-1].state);
+    me->dir = +1;
+    if (me->ourgame->flags & SOLVE_ANIMATES) {
+        me->oldstate = me->ourgame->dup_game(me->states[me->statepos-2].state);
+        me->anim_time =
+            me->ourgame->anim_length(me->states[me->statepos-2].state,
+                                     me->states[me->statepos-1].state,
+                                     +1, me->ui);
+        me->anim_pos = 0.0;
+    } else {
+        me->anim_time = 0.0;
+        midend_finish_move(me);
+    }
+    if (me->drawing)
+        midend_redraw(me);
+    midend_set_timer(me);
+    return NULL;
+}
+
+int midend_status(midend *me)
+{
+    /*
+     * We should probably never be called when the state stack has no
+     * states on it at all - ideally, midends should never be left in
+     * that state for long enough to get put down and forgotten about.
+     * But if we are, I think we return _true_ - pedantically speaking
+     * a midend in that state is 'vacuously solved', and more
+     * practically, a user whose midend has been left in that state
+     * probably _does_ want the 'new game' option to be prominent.
+     */
+    if (me->statepos == 0)
+        return +1;
+
+    return me->ourgame->status(me->states[me->statepos-1].state);
+}
+
+char *midend_rewrite_statusbar(midend *me, char *text)
+{
+    /*
+     * An important special case is that we are occasionally called
+     * with our own laststatus, to update the timer.
+     */
+    if (me->laststatus != text) {
+        sfree(me->laststatus);
+        me->laststatus = dupstr(text);
+    }
+
+    if (me->ourgame->is_timed) {
+        char timebuf[100], *ret;
+        int min, sec;
+
+        sec = (int)me->elapsed;
+        min = sec / 60;
+        sec %= 60;
+        sprintf(timebuf, "[%d:%02d] ", min, sec);
+
+        ret = snewn(strlen(timebuf) + strlen(text) + 1, char);
+        strcpy(ret, timebuf);
+        strcat(ret, text);
+        return ret;
+
+    } else {
+        return dupstr(text);
+    }
+}
+
+#define SERIALISE_MAGIC "Simon Tatham's Portable Puzzle Collection"
+#define SERIALISE_VERSION "1"
+
+/* rockbox kludge */
+static void copy_left_justified(char *buf, size_t sz, const char *str)
+{
+    memset(buf, ' ', sz - 1);
+    int len = strlen(str);
+    if(len <= sz - 1)
+        memcpy(buf, str, len);
+    else
+        fatal("overrun");
+    buf[sz - 1] = 0;
+}
+
+void midend_serialise(midend *me,
+                      void (*write)(void *ctx, void *buf, int len),
+                      void *wctx)
+{
+    int i;
+
+    /*
+     * Each line of the save file contains three components. First
+     * exactly 8 characters of header word indicating what type of
+     * data is contained on the line; then a colon followed by a
+     * decimal integer giving the length of the main string on the
+     * line; then a colon followed by the string itself (exactly as
+     * many bytes as previously specified, no matter what they
+     * contain). Then a newline (of reasonably flexible form).
+     */
+#define wr(h,s) do { \
+    char hbuf[80]; \
+    char *str = (s); \
+    char lbuf[9]; \
+    copy_left_justified(lbuf, sizeof(lbuf), h); \
+    sprintf(hbuf, "%s:%d:", lbuf, (int)strlen(str)); \
+    write(wctx, hbuf, strlen(hbuf)); \
+    write(wctx, str, strlen(str)); \
+    write(wctx, "\n", 1); \
+} while (0)
+
+    /*
+     * Magic string identifying the file, and version number of the
+     * file format.
+     */
+    wr("SAVEFILE", SERIALISE_MAGIC);
+    wr("VERSION", SERIALISE_VERSION);
+
+    /*
+     * The game name. (Copied locally to avoid const annoyance.)
+     */
+    {
+        char *s = dupstr(me->ourgame->name);
+        wr("GAME", s);
+        sfree(s);
+    }
+
+    /*
+     * The current long-term parameters structure, in full.
+     */
+    if (me->params) {
+        char *s = me->ourgame->encode_params(me->params, TRUE);
+        wr("PARAMS", s);
+        sfree(s);
+    }
+
+    /*
+     * The current short-term parameters structure, in full.
+     */
+    if (me->curparams) {
+        char *s = me->ourgame->encode_params(me->curparams, TRUE);
+        wr("CPARAMS", s);
+        sfree(s);
+    }
+
+    /*
+     * The current game description, the privdesc, and the random seed.
+     */
+    if (me->seedstr)
+        wr("SEED", me->seedstr);
+    if (me->desc)
+        wr("DESC", me->desc);
+    if (me->privdesc)
+        wr("PRIVDESC", me->privdesc);
+
+    /*
+     * The game's aux_info. We obfuscate this to prevent spoilers
+     * (people are likely to run `head' or similar on a saved game
+     * file simply to find out what it is, and don't necessarily
+     * want to be told the answer to the puzzle!)
+     */
+    if (me->aux_info) {
+        unsigned char *s1;
+        char *s2;
+        int len;
+
+        len = strlen(me->aux_info);
+        s1 = snewn(len, unsigned char);
+        memcpy(s1, me->aux_info, len);
+        obfuscate_bitmap(s1, len*8, FALSE);
+        s2 = bin2hex(s1, len);
+
+        wr("AUXINFO", s2);
+
+        sfree(s2);
+        sfree(s1);
+    }
+
+    /*
+     * Any required serialisation of the game_ui.
+     */
+    if (me->ui) {
+        char *s = me->ourgame->encode_ui(me->ui);
+        if (s) {
+            wr("UI", s);
+            sfree(s);
+        }
+    }
+
+    /*
+     * The game time, if it's a timed game.
+     */
+    if (me->ourgame->is_timed) {
+        char buf[80];
+        sprintf(buf, "%g", me->elapsed);
+        wr("TIME", buf);
+    }
+
+    /*
+     * The length of, and position in, the states list.
+     */
+    {
+        char buf[80];
+        sprintf(buf, "%d", me->nstates);
+        wr("NSTATES", buf);
+        sprintf(buf, "%d", me->statepos);
+        wr("STATEPOS", buf);
+    }
+
+    /*
+     * For each state after the initial one (which we know is
+     * constructed from either privdesc or desc), enough
+     * information for execute_move() to reconstruct it from the
+     * previous one.
+     */
+    for (i = 1; i < me->nstates; i++) {
+        assert(me->states[i].movetype != NEWGAME);   /* only state 0 */
+        switch (me->states[i].movetype) {
+          case MOVE:
+            wr("MOVE", me->states[i].movestr);
+            break;
+          case SOLVE:
+            wr("SOLVE", me->states[i].movestr);
+            break;
+          case RESTART:
+            wr("RESTART", me->states[i].movestr);
+            break;
+        }
+    }
+
+#undef wr
+}
+
+/*
+ * This function returns NULL on success, or an error message.
+ */
+char *midend_deserialise(midend *me,
+                         int (*read)(void *ctx, void *buf, int len),
+                         void *rctx)
+{
+    int nstates = 0, statepos = -1, gotstates = 0;
+    int started = FALSE;
+    int i;
+
+    char *val = NULL;
+    /* Initially all errors give the same report */
+    char *ret = "Data does not appear to be a saved game file";
+
+    /*
+     * We construct all the new state in local variables while we
+     * check its sanity. Only once we have finished reading the
+     * serialised data and detected no errors at all do we start
+     * modifying stuff in the midend passed in.
+     */
+    char *seed = NULL, *parstr = NULL, *desc = NULL, *privdesc = NULL;
+    char *auxinfo = NULL, *uistr = NULL, *cparstr = NULL;
+    float elapsed = 0.0F;
+    game_params *params = NULL, *cparams = NULL;
+    game_ui *ui = NULL;
+    struct midend_state_entry *states = NULL;
+
+    /*
+     * Loop round and round reading one key/value pair at a time
+     * from the serialised stream, until we have enough game states
+     * to finish.
+     */
+    while (nstates <= 0 || statepos < 0 || gotstates < nstates-1) {
+        char key[9], c;
+        int len;
+
+        do {
+            if (!read(rctx, key, 1)) {
+                /* unexpected EOF */
+                goto cleanup;
+            }
+        } while (key[0] == '\r' || key[0] == '\n');
+
+        if (!read(rctx, key+1, 8)) {
+            /* unexpected EOF */
+            goto cleanup;
+        }
+
+        if (key[8] != ':') {
+            if (started)
+                ret = "Data was incorrectly formatted for a saved game file";
+            goto cleanup;
+        }
+        len = strcspn(key, ": ");
+        assert(len <= 8);
+        key[len] = '\0';
+
+        len = 0;
+        while (1) {
+            if (!read(rctx, &c, 1)) {
+                /* unexpected EOF */
+                goto cleanup;
+            }
+
+            if (c == ':') {
+                break;
+            } else if (c >= '0' && c <= '9') {
+                len = (len * 10) + (c - '0');
+            } else {
+                if (started)
+                    ret = "Data was incorrectly formatted for a"
+                    " saved game file";
+                goto cleanup;
+            }
+        }
+
+        val = snewn(len+1, char);
+        if (!read(rctx, val, len)) {
+            if (started)
+            goto cleanup;
+        }
+        val[len] = '\0';
+
+        if (!started) {
+            if (strcmp(key, "SAVEFILE") || strcmp(val, SERIALISE_MAGIC)) {
+                /* ret already has the right message in it */
+                goto cleanup;
+            }
+            /* Now most errors are this one, unless otherwise specified */
+            ret = "Saved data ended unexpectedly";
+            started = TRUE;
+        } else {
+            if (!strcmp(key, "VERSION")) {
+                if (strcmp(val, SERIALISE_VERSION)) {
+                    ret = "Cannot handle this version of the saved game"
+                        " file format";
+                    goto cleanup;
+                }
+            } else if (!strcmp(key, "GAME")) {
+                if (strcmp(val, me->ourgame->name)) {
+                    ret = "Save file is from a different game";
+                    goto cleanup;
+                }
+            } else if (!strcmp(key, "PARAMS")) {
+                sfree(parstr);
+                parstr = val;
+                val = NULL;
+            } else if (!strcmp(key, "CPARAMS")) {
+                sfree(cparstr);
+                cparstr = val;
+                val = NULL;
+            } else if (!strcmp(key, "SEED")) {
+                sfree(seed);
+                seed = val;
+                val = NULL;
+            } else if (!strcmp(key, "DESC")) {
+                sfree(desc);
+                desc = val;
+                val = NULL;
+            } else if (!strcmp(key, "PRIVDESC")) {
+                sfree(privdesc);
+                privdesc = val;
+                val = NULL;
+            } else if (!strcmp(key, "AUXINFO")) {
+                unsigned char *tmp;
+                int len = strlen(val) / 2;   /* length in bytes */
+                tmp = hex2bin(val, len);
+                obfuscate_bitmap(tmp, len*8, TRUE);
+
+                sfree(auxinfo);
+                auxinfo = snewn(len + 1, char);
+                memcpy(auxinfo, tmp, len);
+                auxinfo[len] = '\0';
+                sfree(tmp);
+            } else if (!strcmp(key, "UI")) {
+                sfree(uistr);
+                uistr = val;
+                val = NULL;
+            } else if (!strcmp(key, "TIME")) {
+                elapsed = (float)atof(val);
+            } else if (!strcmp(key, "NSTATES")) {
+                nstates = atoi(val);
+                if (nstates <= 0) {
+                    ret = "Number of states in save file was negative";
+                    goto cleanup;
+                }
+                if (states) {
+                    ret = "Two state counts provided in save file";
+                    goto cleanup;
+                }
+                states = snewn(nstates, struct midend_state_entry);
+                for (i = 0; i < nstates; i++) {
+                    states[i].state = NULL;
+                    states[i].movestr = NULL;
+                    states[i].movetype = NEWGAME;
+                }
+            } else if (!strcmp(key, "STATEPOS")) {
+                statepos = atoi(val);
+            } else if (!strcmp(key, "MOVE")) {
+                gotstates++;
+                states[gotstates].movetype = MOVE;
+                states[gotstates].movestr = val;
+                val = NULL;
+            } else if (!strcmp(key, "SOLVE")) {
+                gotstates++;
+                states[gotstates].movetype = SOLVE;
+                states[gotstates].movestr = val;
+                val = NULL;
+            } else if (!strcmp(key, "RESTART")) {
+                gotstates++;
+                states[gotstates].movetype = RESTART;
+                states[gotstates].movestr = val;
+                val = NULL;
+            }
+        }
+
+        sfree(val);
+        val = NULL;
+    }
+
+    params = me->ourgame->default_params();
+    me->ourgame->decode_params(params, parstr);
+    if (me->ourgame->validate_params(params, TRUE)) {
+        ret = "Long-term parameters in save file are invalid";
+        goto cleanup;
+    }
+    cparams = me->ourgame->default_params();
+    me->ourgame->decode_params(cparams, cparstr);
+    if (me->ourgame->validate_params(cparams, FALSE)) {
+        ret = "Short-term parameters in save file are invalid";
+        goto cleanup;
+    }
+    if (seed && me->ourgame->validate_params(cparams, TRUE)) {
+        /*
+         * The seed's no use with this version, but we can perfectly
+         * well use the rest of the data.
+         */
+        sfree(seed);
+        seed = NULL;
+    }
+    if (!desc) {
+        ret = "Game description in save file is missing";
+        goto cleanup;
+    } else if (me->ourgame->validate_desc(params, desc)) {
+        ret = "Game description in save file is invalid";
+        goto cleanup;
+    }
+    if (privdesc && me->ourgame->validate_desc(params, privdesc)) {
+        ret = "Game private description in save file is invalid";
+        goto cleanup;
+    }
+    if (statepos < 0 || statepos >= nstates) {
+        ret = "Game position in save file is out of range";
+    }
+
+    states[0].state = me->ourgame->new_game(me, params,
+                                            privdesc ? privdesc : desc);
+    for (i = 1; i < nstates; i++) {
+        assert(states[i].movetype != NEWGAME);
+        switch (states[i].movetype) {
+          case MOVE:
+          case SOLVE:
+            states[i].state = me->ourgame->execute_move(states[i-1].state,
+                                                        states[i].movestr);
+            if (states[i].state == NULL) {
+                ret = "Save file contained an invalid move";
+                goto cleanup;
+            }
+            break;
+          case RESTART:
+            if (me->ourgame->validate_desc(params, states[i].movestr)) {
+                ret = "Save file contained an invalid restart move";
+                goto cleanup;
+            }
+            states[i].state = me->ourgame->new_game(me, params,
+                                                    states[i].movestr);
+            break;
+        }
+    }
+
+    ui = me->ourgame->new_ui(states[0].state);
+    me->ourgame->decode_ui(ui, uistr);
+
+    /*
+     * Now we've run out of possible error conditions, so we're
+     * ready to start overwriting the real data in the current
+     * midend. We'll do this by swapping things with the local
+     * variables, so that the same cleanup code will free the old
+     * stuff.
+     */
+    {
+        char *tmp;
+
+        tmp = me->desc;
+        me->desc = desc;
+        desc = tmp;
+
+        tmp = me->privdesc;
+        me->privdesc = privdesc;
+        privdesc = tmp;
+
+        tmp = me->seedstr;
+        me->seedstr = seed;
+        seed = tmp;
+
+        tmp = me->aux_info;
+        me->aux_info = auxinfo;
+        auxinfo = tmp;
+    }
+
+    me->genmode = GOT_NOTHING;
+
+    me->statesize = nstates;
+    nstates = me->nstates;
+    me->nstates = me->statesize;
+    {
+        struct midend_state_entry *tmp;
+        tmp = me->states;
+        me->states = states;
+        states = tmp;
+    }
+    me->statepos = statepos;
+
+    {
+        game_params *tmp;
+
+        tmp = me->params;
+        me->params = params;
+        params = tmp;
+
+        tmp = me->curparams;
+        me->curparams = cparams;
+        cparams = tmp;
+    }
+
+    me->oldstate = NULL;
+    me->anim_time = me->anim_pos = me->flash_time = me->flash_pos = 0.0F;
+    me->dir = 0;
+
+    {
+        game_ui *tmp;
+
+        tmp = me->ui;
+        me->ui = ui;
+        ui = tmp;
+    }
+
+    me->elapsed = elapsed;
+    me->pressed_mouse_button = 0;
+
+    midend_set_timer(me);
+
+    if (me->drawstate)
+        me->ourgame->free_drawstate(me->drawing, me->drawstate);
+    me->drawstate =
+        me->ourgame->new_drawstate(me->drawing,
+                                   me->states[me->statepos-1].state);
+    midend_size_new_drawstate(me);
+
+    ret = NULL;                        /* success! */
+
+    cleanup:
+    sfree(val);
+    sfree(seed);
+    sfree(parstr);
+    sfree(cparstr);
+    sfree(desc);
+    sfree(privdesc);
+    sfree(auxinfo);
+    sfree(uistr);
+    if (params)
+        me->ourgame->free_params(params);
+    if (cparams)
+        me->ourgame->free_params(cparams);
+    if (ui)
+        me->ourgame->free_ui(ui);
+    if (states) {
+        int i;
+
+        for (i = 0; i < nstates; i++) {
+            if (states[i].state)
+                me->ourgame->free_game(states[i].state);
+            sfree(states[i].movestr);
+        }
+        sfree(states);
+    }
+
+    return ret;
+}
+
+/*
+ * This function examines a saved game file just far enough to
+ * determine which game type it contains. It returns NULL on success
+ * and the game name string in 'name' (which will be dynamically
+ * allocated and should be caller-freed), or an error message on
+ * failure.
+ */
+char *identify_game(char **name, int (*read)(void *ctx, void *buf, int len),
+                    void *rctx)
+{
+    int nstates = 0, statepos = -1, gotstates = 0;
+    int started = FALSE;
+
+    char *val = NULL;
+    /* Initially all errors give the same report */
+    char *ret = "Data does not appear to be a saved game file";
+
+    *name = NULL;
+
+    /*
+     * Loop round and round reading one key/value pair at a time from
+     * the serialised stream, until we've found the game name.
+     */
+    while (nstates <= 0 || statepos < 0 || gotstates < nstates-1) {
+        char key[9], c;
+        int len;
+
+        do {
+            if (!read(rctx, key, 1)) {
+                /* unexpected EOF */
+                goto cleanup;
+            }
+        } while (key[0] == '\r' || key[0] == '\n');
+
+        if (!read(rctx, key+1, 8)) {
+            /* unexpected EOF */
+            goto cleanup;
+        }
+
+        if (key[8] != ':') {
+            if (started)
+                ret = "Data was incorrectly formatted for a saved game file";
+            goto cleanup;
+        }
+        len = strcspn(key, ": ");
+        assert(len <= 8);
+        key[len] = '\0';
+
+        len = 0;
+        while (1) {
+            if (!read(rctx, &c, 1)) {
+                /* unexpected EOF */
+                goto cleanup;
+            }
+
+            if (c == ':') {
+                break;
+            } else if (c >= '0' && c <= '9') {
+                len = (len * 10) + (c - '0');
+            } else {
+                if (started)
+                    ret = "Data was incorrectly formatted for a"
+                    " saved game file";
+                goto cleanup;
+            }
+        }
+
+        val = snewn(len+1, char);
+        if (!read(rctx, val, len)) {
+            if (started)
+            goto cleanup;
+        }
+        val[len] = '\0';
+
+        if (!started) {
+            if (strcmp(key, "SAVEFILE") || strcmp(val, SERIALISE_MAGIC)) {
+                /* ret already has the right message in it */
+                goto cleanup;
+            }
+            /* Now most errors are this one, unless otherwise specified */
+            ret = "Saved data ended unexpectedly";
+            started = TRUE;
+        } else {
+            if (!strcmp(key, "VERSION")) {
+                if (strcmp(val, SERIALISE_VERSION)) {
+                    ret = "Cannot handle this version of the saved game"
+                        " file format";
+                    goto cleanup;
+                }
+            } else if (!strcmp(key, "GAME")) {
+                *name = dupstr(val);
+                ret = NULL;
+                goto cleanup;
+            }
+        }
+
+        sfree(val);
+        val = NULL;
+    }
+
+    cleanup:
+    sfree(val);
+    return ret;
+}
+
+char *midend_print_puzzle(midend *me, document *doc, int with_soln)
+{
+    game_state *soln = NULL;
+
+    if (me->statepos < 1)
+        return "No game set up to print";/* _shouldn't_ happen! */
+
+    if (with_soln) {
+        char *msg, *movestr;
+
+        if (!me->ourgame->can_solve)
+            return "This game does not support the Solve operation";
+
+        msg = "Solve operation failed";/* game _should_ overwrite on error */
+        movestr = me->ourgame->solve(me->states[0].state,
+                                     me->states[me->statepos-1].state,
+                                     me->aux_info, &msg);
+        if (!movestr)
+            return msg;
+        soln = me->ourgame->execute_move(me->states[me->statepos-1].state,
+                                         movestr);
+        assert(soln);
+
+        sfree(movestr);
+    } else
+        soln = NULL;
+
+    /*
+     * This call passes over ownership of the two game_states and
+     * the game_params. Hence we duplicate the ones we want to
+     * keep, and we don't have to bother freeing soln if it was
+     * non-NULL.
+     */
+    document_add_puzzle(doc, me->ourgame,
+                        me->ourgame->dup_params(me->curparams),
+                        me->ourgame->dup_game(me->states[0].state), soln);
+
+    return NULL;
+}