Special-case right-dragging of a numbered cell off the grid.

Chris Boyle reports that if you right-drag a numbered cell off the
grid, _all_ numbered cells (except the immutable initial clues) get
reset to blank, because this is treated as an attempt to erase a whole
chain of linked cells (of the form a,a+1,...,a_k) and the cells with
definite numbers are all treated as 'chain 0'.

In that situation, I now substitute the same behaviour you'd get by
left-dragging the numbered cell off the board, i.e. erase _just_ that
cell and not the whole of the rest of the puzzle.

(The previous unintended behaviour was a UI action you surely never
want - and Chris also reports that due to the Android front end's way
of representing right-drags, it's especially easy to hit by mistake.)

1 files changed, 5 insertions, 2 deletions

diff --git a/signpost.c b/signpost.c
index 9dd8699..f0784eb 100644
--- a/signpost.c
+++ b/signpost.c
@@ -1578,6 +1578,8 @@ static game_state *execute_move(const game_state *state, const char *move)
         si = sy*w+sx; ei = ey*w+ex;
         makelink(ret, si, ei);
     } else if (sscanf(move, "%c%d,%d", &c, &sx, &sy) == 3) {
+        int sset;
+
         if (c != 'C' && c != 'X') return NULL;
         if (!INGRID(state, sx, sy)) return NULL;
         si = sy*w+sx;
@@ -1586,11 +1588,12 @@ static game_state *execute_move(const game_state *state, const char *move)
 
         ret = dup_game(state);
 
-        if (c == 'C') {
+        sset = state->nums[si] / (state->n+1);
+        if (c == 'C' || (c == 'X' && sset == 0)) {
             /* Unlink the single cell we dragged from the board. */
             unlink_cell(ret, si);
         } else {
-            int i, set, sset = state->nums[si] / (state->n+1);
+            int i, set;
             for (i = 0; i < state->n; i++) {
                 /* Unlink all cells in the same set as the one we dragged
                  * from the board. */