-static char *interpret_move(game_state *from, game_ui *ui, game_drawstate *ds,
+static char *interpret_move(game_state *from, game_ui *ui, const game_drawstate *ds,
int x, int y, int button)
{
int over_col = 0; /* one-indexed */
int x, int y, int button)
{
int over_col = 0; /* one-indexed */