X-Git-Url: https://git.distorted.org.uk/~mdw/sgt/puzzles/blobdiff_plain/787cfc9603b6fadab6cf2c36a5609ae369022c4f..1733f4cabcbe57cbee99191915d8fd54cab7f18e:/HACKING.but

diff --git a/HACKING.but b/HACKING.but
index f6c93f0..e1abf75 100644
--- a/HACKING.but
+++ b/HACKING.but
@@ -166,7 +166,8 @@ chronological order, the second one contains the direction field
 which corresponds to the actual difference between the states.
 However, when it is passed a pair of states in the opposite order
 due to an undo, it should be looking in the \e{first} one to find
-the direction field. Sixteen solves this by also storing the current
-move count in the game state, so that \cw{game_redraw()} can compare
-the two move counts to work out whether it's drawing an undo or not,
-and look in the right place for the direction field.
+the direction field.
+
+For this reason, in the redraw functions you are provided with an
+extra argument \c{dir} which tells you which state was chronologically
+first; \c{dir} is +1 for a normal move and -1 for an undo.