X-Git-Url: https://git.distorted.org.uk/~mdw/sgt/puzzles/blobdiff_plain/f2512854af2d70f311701fa81dbafef8ee0de929..HEAD:/devel.but

diff --git a/devel.but b/devel.but
index 27ef5d7..970a73a 100644
--- a/devel.but
+++ b/devel.but
@@ -856,7 +856,7 @@ producing new \c{game_state}s.
 \S{backend-interpret-move} \cw{interpret_move()}
 
 \c char *(*interpret_move)(game_state *state, game_ui *ui,
-\c                         game_drawstate *ds,
+\c                         const game_drawstate *ds,
 \c                         int x, int y, int button);
 
 This function receives user input and processes it. Its input
@@ -868,6 +868,11 @@ indicating an arrow or function key or a mouse event; when
 coordinates of the mouse pointer relative to the top left of the
 puzzle's drawing area.
 
+(The pointer to the \c{game_drawstate} is marked \c{const}, because
+\c{interpret_move} should not write to it. The normal use of that
+pointer will be to read the game's tile size parameter in order to
+divide mouse coordinates by it.)
+
 \cw{interpret_move()} may return in three different ways:
 
 \b Returning \cw{NULL} indicates that no action whatsoever occurred