feat: account for mobility in evaluation

1 files changed, 21 insertions, 4 deletions

diff --git a/src/board/engine.rs b/src/board/engine.rs
index dcb3646..d00b89b 100644
--- a/src/board/engine.rs
+++ b/src/board/engine.rs
@@ -99,13 +99,29 @@ impl Board {
         eval
     }
 
+    /// Evaluate a position relative to the current player
+    pub fn evaluate(&self, precomputed_mobility: Option<f32>) -> f32 {
+        let opponent_mobility = self.mobility(self.color().flip());
+        let player_mobility = match precomputed_mobility {
+            Some(m) => m,
+            None => self.mobility(self.color()),
+        };
+        let mobility_advantage = player_mobility - opponent_mobility as f32;
+
+        let material_advantage = self.material_advantage();
+
+        material_advantage + 0.1 * mobility_advantage
+    }
+
     pub fn negamax_search(&mut self, mut alpha: f32, beta: f32, depth_left: u8) -> (f32, Vec<Move>) {
         let mut principal_variation = Vec::new();
         let color = self.color();
+
+        let moves = self.generate_pseudolegal_moves(color);
+
         if depth_left == 0 {
-            return (self.material_advantage(), principal_variation);
+            return (self.evaluate(Some(moves.len() as f32)), principal_variation);
         }
-        let moves = self.generate_pseudolegal_moves(color);
 
         for mov in moves {
             let ep_target_before = self.ep_target.clone();
@@ -135,7 +151,9 @@ impl Board {
 
     pub fn quiscence(&mut self, mut alpha: f32, beta: f32) -> f32 {
         let color = self.color();
-        let stand_pat = self.material_advantage();
+        let moves = self.generate_pseudolegal_moves(color);
+
+        let stand_pat = self.evaluate(Some(moves.len() as f32));
 
         if stand_pat >= beta {
             return beta;
@@ -144,7 +162,6 @@ impl Board {
             alpha = stand_pat;
         }
 
-        let moves = self.generate_pseudolegal_moves(color);
         let tactical_moves = moves.iter().filter(|m| m.kind == MoveKind::Capture || m.kind == MoveKind::EnPassant);
 
         for mov in tactical_moves {