Initial work on rollback and refactor

src/fighter/state/ground.rs

@@ -0,0 +1,55 @@
+//! Ground movement math shared by every grounded state. Deliberately free of
+//! ECS types so it stays cheap to reason about and to unit-test — it has to be
+//! bit-for-bit deterministic for rollback.
+
+use crate::fighter::FighterAttributes;
+use crate::game_settings::GameSettings;
+
+pub fn apply_grounded_friction(friction: f32, ground_vel: f32) -> f32 {
+    if friction.abs() > ground_vel.abs() {
+        -ground_vel
+    } else {
+        (-ground_vel.signum()) * friction.abs()
+    }
+}
+
+pub fn move_accelerate() {}
+
+pub fn compute_ground_accel(
+    accel: f32,
+    target_vel: f32,
+    gr_vel: f32,
+    attribs: &FighterAttributes,
+    game_settings: &GameSettings,
+) -> f32 {
+    if target_vel == 0.0 {
+        apply_grounded_friction(attribs.ground_friction, gr_vel)
+    } else {
+        let mut accel = accel;
+        let ground_max_horizontal_velocity =
+            game_settings.figher_common.ground_max_horizontal_velocity;
+        if !(gr_vel * accel < 0.0) {
+            // accelerating, not reversing
+            if accel > 0.0 {
+                if gr_vel + accel > target_vel {
+                    accel = -attribs.ground_friction;
+                    if gr_vel + accel < target_vel {
+                        accel = target_vel - gr_vel;
+                    }
+                    if gr_vel + accel > ground_max_horizontal_velocity {
+                        accel = ground_max_horizontal_velocity - gr_vel;
+                    }
+                }
+            } else if gr_vel + accel < target_vel {
+                accel = attribs.ground_friction;
+                if gr_vel + accel > target_vel {
+                    accel = target_vel - gr_vel;
+                }
+                if gr_vel + accel < -ground_max_horizontal_velocity {
+                    accel = -ground_max_horizontal_velocity - gr_vel;
+                }
+            }
+        }
+        accel
+    }
+}