Eliminate movement side-effect

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

lib/features/renderer/renderer.dart

@@ -190,7 +190,14 @@ class _WolfRendererState extends State<WolfRenderer>
     if (player.angle < 0) player.angle += 2 * math.pi;
     if (player.angle >= 2 * math.pi) player.angle -= 2 * math.pi;
 
-    _applyMovementAndCollision(inputResult.movement);
+    Coordinate2D validatedPos = _calculateValidatedPosition(
+      player.position,
+      inputResult.movement,
+    );
+
+    player.x = validatedPos.x;
+    player.y = validatedPos.y;
+
     _updateEntities(elapsed);
 
     // Explicit reassignment from a pure(r) function
@@ -258,33 +265,40 @@ class _WolfRendererState extends State<WolfRenderer>
     return (movement: movement, dAngle: dAngle);
   }
 
-  void _applyMovementAndCollision(Coordinate2D movement) {
+  Coordinate2D _calculateValidatedPosition(
+    Coordinate2D currentPos,
+    Coordinate2D movement,
+  ) {
     const double margin = 0.3;
+    double newX = currentPos.x;
+    double newY = currentPos.y;
 
-    // Calculate the intended new position
-    Coordinate2D newPos = player.position + movement;
+    // Calculate potential new coordinates
+    Coordinate2D target = currentPos + movement;
 
-    // Check X axis independently (allows for sliding along walls)
+    // Validate X (allows sliding along walls)
     if (movement.x != 0) {
       int checkX = (movement.x > 0)
-          ? (newPos.x + margin).toInt()
-          : (newPos.x - margin).toInt();
+          ? (target.x + margin).toInt()
+          : (target.x - margin).toInt();
 
-      if (_isWalkable(checkX, player.position.y.toInt())) {
-        player.x = newPos.x;
+      if (_isWalkable(checkX, currentPos.y.toInt())) {
+        newX = target.x;
       }
     }
 
-    // Check Y axis independently
+    // Validate Y
     if (movement.y != 0) {
       int checkY = (movement.y > 0)
-          ? (newPos.y + margin).toInt()
-          : (newPos.y - margin).toInt();
+          ? (target.y + margin).toInt()
+          : (target.y - margin).toInt();
 
-      if (_isWalkable(player.position.x.toInt(), checkY)) {
-        player.y = newPos.y;
+      if (_isWalkable(newX.toInt(), checkY)) {
+        newY = target.y;
       }
     }
+
+    return Coordinate2D(newX, newY);
   }
 
   void _updateEntities(Duration elapsed) {