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Ensure the shuffling process never produces an already-solved grid.

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[originally from svn r7446]
This commit is contained in:
Simon Tatham
2007-04-04 19:12:17 +00:00
parent f6a7276495
commit 61395a5141
1 changed files with 48 additions and 6 deletions
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54
net.c
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@ -1403,13 +1403,55 @@ static char *new_game_desc(game_params *params, random_state *rs,
/*
* Now shuffle the grid.
*
* In order to avoid accidentally generating an already-solved
* grid, we will reshuffle as necessary to ensure that at least
* one edge has a mismatched connection.
*
* This can always be done, since validate_params() enforces a
* grid area of at least 2 and our generator never creates
* either type of rotationally invariant tile (cross and
* blank). Hence there must be at least one edge separating
* distinct tiles, and it must be possible to find orientations
* of those tiles such that one tile is trying to connect
* through that edge and the other is not.
*
* (We could be more subtle, and allow the shuffle to generate
* a grid in which all tiles match up locally and the only
* criterion preventing the grid from being already solved is
* connectedness. However, that would take more effort, and
* it's easier to simply make sure every grid is _obviously_
* not solved.)
*/
for (y = 0; y < h; y++) {
for (x = 0; x < w; x++) {
int orig = index(params, tiles, x, y);
int rot = random_upto(rs, 4);
index(params, tiles, x, y) = ROT(orig, rot);
}
while (1) {
int mismatches;
for (y = 0; y < h; y++) {
for (x = 0; x < w; x++) {
int orig = index(params, tiles, x, y);
int rot = random_upto(rs, 4);
index(params, tiles, x, y) = ROT(orig, rot);
}
}
mismatches = 0;
/*
* I can't even be bothered to check for mismatches across
* a wrapping edge, so I'm just going to enforce that there
* must be a mismatch across a non-wrapping edge, which is
* still always possible.
*/
for (y = 0; y < h; y++) for (x = 0; x < w; x++) {
if (x+1 < w && ((ROT(index(params, tiles, x, y), 2) ^
index(params, tiles, x+1, y)) & L))
mismatches++;
if (y+1 < h && ((ROT(index(params, tiles, x, y), 2) ^
index(params, tiles, x, y+1)) & U))
mismatches++;
}
if (mismatches > 0)
break;
}
/*