Clear any existing Tracks flash data when generating it

Simon points out that if you have an ambiguous puzzle then it might
need different flash data for different solutions, so if you solve it
one way, than manually unsolve it and solve it another way, the old
flash data in the game state need to be cleared out when the new flash
data are written.

Tested by solving the hugely ambiguous "5x5:CwC,5,5,5,5,S5,S5,5,5,5,5".

1 files changed, 5 insertions, 3 deletions

diff --git a/tracks.c b/tracks.c
index 2fad011..00a2b31 100644
--- a/tracks.c
+++ b/tracks.c
@@ -242,7 +242,8 @@ static const int nbits[] = { 0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4 };
 #define S_CLUE 8
 #define S_MARK 16
 
-#define S_FLASH_SHIFT   8  /* Position of tile in solved track, 8 bits */
+#define S_FLASH_SHIFT   8  /* Position of tile in solved track */
+#define S_FLASH_WIDTH   8  /* Width of above sub-field */
 #define S_TRACK_SHIFT   16 /* U/D/L/R flags for edge track indicators */
 #define S_NOTRACK_SHIFT 20 /* U/D/L/R flags for edge no-track indicators */
 
@@ -1836,8 +1837,9 @@ static void set_flash_data(game_state *state)
         ntrack += state->numbers->numbers[x];
     n = 0; x = 0; y = state->numbers->row_s; d = R;
     do {
-        /* Don't bother clearing; this only runs at completion. */
-        state->sflags[y*w + x] |= (n++ * 255 / (ntrack - 1)) << S_FLASH_SHIFT;
+        state->sflags[y*w + x] &= ~(((1<<S_FLASH_WIDTH) - 1) << S_FLASH_SHIFT);
+        state->sflags[y*w + x] |=
+            (n++ * ((1<<S_FLASH_WIDTH) - 1) / (ntrack - 1)) << S_FLASH_SHIFT;
         d = F(d); /* Find the direction we just arrived from. */
         d = S_E_DIRS(state, x, y, E_TRACK) & ~d; /* Other track from here. */
         x += DX(d); y += DY(d); /* Move to the next tile. */