Special client rendering: Do explain why not to provide xdata here

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/src/gamestate.rs b/src/gamestate.rs
index e649864b9c20342daa946de16bbb0a3941aa78b3..c35b0f7bb64a1da3ba434afba2ecf95bf0660fcf 100644 (file)
--- a/src/gamestate.rs
+++ b/src/gamestate.rs
@@ -180,6 +180,10 @@ pub trait PieceBaseTrait: OutlineTrait + Send + Debug + 'static {
 
   fn itemname(&self) -> &str;
 
+  // Don't add an xdata argument to this.  Implementors must not make
+  // this depend on the piece state, because the piece state might change
+  // between svg() (which sets up information in the DOM) and special()
+  // (which arranges to use that information).
   fn special(&self) -> Result<Option<SpecialClientRendering>,IE> { Ok(None) }
 }