New backend function: current_key_label()

This provides a way for the front end to ask how a particular key should
be labelled right now (specifically, for a given game_state and
game_ui).  This is useful on feature phones where it's conventional to
put a small caption above each soft key indicating what it currently
does.

The function currently provides labels only for CURSOR_SELECT and
CURSOR_SELECT2.  This is because these are the only keys that need
labelling on KaiOS.

The concept of labelling keys also turns up in the request_keys() call,
but there are quite a few differences.  The labels returned by
current_key_label() are dynamic and likely to vary with each move, while
the labels provided by request_keys() are constant for a given
game_params.  Also, the keys returned by request_keys() don't generally
include CURSOR_SELECT and CURSOR_SELECT2, because those aren't necessary
on platforms with pointing devices.  It might be possible to provide a
unified API covering both of this, but I think it would be quite
difficult to work with.

Where a key is to be unlabelled, current_key_label() is expected to
return an empty string.  This leaves open the possibility of NULL
indicating a fallback to button2label or the label specified by
request_keys() in the future.

It's tempting to try to implement current_key_label() by calling
interpret_move() and parsing its output.  This doesn't work for two
reasons.  One is that interpret_move() is entitled to modify the
game_ui, and there isn't really a practical way to back those changes
out.  The other is that the information returned by interpret_move()
isn't sufficient to generate a label.  For instance, in many puzzles it
generates moves that toggle the state of a square, but we want the label
to reflect which state the square will be toggled to.  The result is
that I've generally ended up pulling bits of code from interpret_move()
and execute_move() together to implement current_key_label().

Alongside the back-end function, there's a midend_current_key_label()
that's a thin wrapper around the back-end function.  It just adds an
assertion about which key's being requested and a default null
implementation so that back-ends can avoid defining the function if it
will do nothing useful.

1 files changed, 20 insertions, 0 deletions

diff --git a/samegame.c b/samegame.c
index 22b4316..3597e19 100644
--- a/samegame.c
+++ b/samegame.c
@@ -1109,6 +1109,25 @@ static void game_changed_state(game_ui *ui, const game_state *oldstate,
 	ui->displaysel = false;
 }
 
+static const char *current_key_label(const game_ui *ui,
+                                     const game_state *state, int button)
+{
+    if (IS_CURSOR_SELECT(button)) {
+        int x = ui->xsel, y = ui->ysel, c = COL(state,x,y);
+        if (c == 0) return "";
+        if (ISSEL(ui, x, y))
+            return button == CURSOR_SELECT2 ? "Unselect" : "Remove";
+        if ((x > 0 && COL(state,x-1,y) == c) ||
+            (x+1 < state->params.w && COL(state,x+1,y) == c) ||
+            (y > 0 && COL(state,x,y-1) == c) ||
+            (y+1 < state->params.h && COL(state,x,y+1) == c))
+            return "Select";
+        /* Cursor is over a lone square, so we can't select it. */
+        if (ui->nselected) return "Unselect";
+    }
+    return "";
+}
+
 static char *sel_movedesc(game_ui *ui, const game_state *state)
 {
     int i;
@@ -1670,6 +1689,7 @@ const struct game thegame = {
     decode_ui,
     NULL, /* game_request_keys */
     game_changed_state,
+    current_key_label,
     interpret_move,
     execute_move,
     PREFERRED_TILE_SIZE, game_compute_size, game_set_size,