OptiFine entity models: the local player's model knows when it's in water

Its fluids were never set, so swimming read as crawling for its
animations.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

crates/horizon-client/src/game/perspective.rs

@@ -427,6 +427,7 @@ impl Game<'_> {
         let visually_swimming =
             p.pose == Pose::Swimming || (!p.fall_flying && p.pose == Pose::FallFlying);
         let in_water = p.fluids.was_touching_water;
+        let in_lava = p.is_in_lava();
         let (yaw, pitch) = (self.yaw, self.pitch);
         let main = self.inventory[self.selected].clone();
         let off = self.offhand.as_ref().map(|s| s.item.clone());
@@ -497,6 +498,9 @@ impl Game<'_> {
         m.extra.crouching = crouching;
         // Guests and server players take their pose from DATA_POSE, not here.
         m.extra.avatar_pose = pose;
+        // What custom entity model animations read of the fluids (`is_in_water`, crawling).
+        m.fluids.in_water = in_water;
+        m.fluids.in_lava = in_lava;
         m.extra.passenger = riding;
         m.extra.previous_velocity = m.velocity;
         m.velocity = velocity;

crates/horizon-client/src/mobs/cem_anim.rs

@@ -956,6 +956,21 @@ mod tests {
         );
     }
 
+    #[test]
+    fn the_swimming_pose_in_water_swims_without_crawling() {
+        let mut m = mob();
+        m.extra.pose = 3;
+        let model = bone("root", vec![]);
+        let animation = animate(&model, &[("root.tx", "is_swimming + is_crawling * 2")]);
+        let mut read = |in_water: bool| {
+            m.fluids.in_water = in_water;
+            let mut poses = Poses::new(&model);
+            animation.run_in(&Frame::default(), &m, &still(), &mut poses);
+            poses.get("root")[0]
+        };
+        assert_eq!([read(true), read(false)], [1.0, 3.0]);
+    }
+
     #[test]
     fn a_fox_sits_by_its_own_flags() {
         let mut m = mob();