exercise 3.4: simulating a vehicle with controls

lib/chapters/one_vectors/mover.dart

@@ -8,15 +8,13 @@ class Mover {
   late Vector velocity;
   final Size canvasSize;
   late Vector acceleration;
-  late double topSpeed;
   late double mass;
 
   Mover._(
     this.position,
     this.velocity,
     this.canvasSize,
     this.acceleration,
-    this.topSpeed,
     this.mass,
   );
 
@@ -28,15 +26,13 @@ class Mover {
     // constant acceleration initialisation
     acceleration = const Vector(0, 0);
 
-    topSpeed = 10;
     mass = 10;
   }
 
   void updateRandomAcceleration() {
     acceleration = Vector.random();
     acceleration *= (Random().nextDouble() * 4) - 2;
     velocity += acceleration;
-    velocity = velocity.limit(topSpeed);
     position += velocity;
   }
 
@@ -48,7 +44,6 @@ class Mover {
 
   void update() {
     velocity += acceleration;
-    velocity = velocity.limit(topSpeed);
     position += velocity;
 
     acceleration *= 0; // reset acceleration
@@ -79,15 +74,13 @@ class Mover {
     Vector? velocity,
     Size? canvasSize,
     Vector? acceleration,
-    double? topSpeed,
     double? mass,
   }) {
     return Mover._(
       position ?? this.position,
       velocity ?? this.velocity,
       canvasSize ?? this.canvasSize,
       acceleration ?? this.acceleration,
-      topSpeed ?? this.topSpeed,
       mass ?? this.mass,
     );
   }
@@ -98,7 +91,6 @@ class Mover {
       velocity.hashCode ^
       canvasSize.hashCode ^
       acceleration.hashCode ^
-      topSpeed.hashCode ^
       mass.hashCode;
 
   @override
@@ -109,7 +101,6 @@ class Mover {
         velocity == other.velocity &&
         canvasSize == other.canvasSize &&
         acceleration == other.acceleration &&
-        topSpeed == other.topSpeed &&
         mass == other.mass;
   }
 }

lib/chapters/one_vectors/vector.dart

@@ -43,6 +43,11 @@ class Vector {
     return newVector * newMag;
   }
 
+  /// returns the angle of the vector in radians
+  double heading() {
+    return atan2(y, x);
+  }
+
   Vector operator +(covariant Vector v) {
     return Vector(x + v.x, y + v.y);
   }

lib/chapters/one_vectors/vehicle_mover.dart

@@ -3,11 +3,11 @@ import 'vector.dart';
 
 class VehicleMover extends Mover {
   bool isBreaking = false;
+  late double topSpeed;
   static const Vector _deceleration = Vector(0.01, 0);
 
-  VehicleMover(super.canvasSize, double topSpeed) {
+  VehicleMover(super.canvasSize, this.topSpeed) {
     acceleration = const Vector(0, 0);
-    this.topSpeed = topSpeed;
   }
 
   void brake() {
@@ -25,7 +25,11 @@ class VehicleMover extends Mover {
 
   @override
   void update() {
-    super.update();
+    velocity += acceleration;
+    velocity = velocity.limit(topSpeed);
+    position += velocity;
+
+    acceleration *= 0; // reset acceleration
 
     if (isBreaking && velocity.mag() < 1) {
       velocity = Vector.zero;

lib/chapters/three_oscillation/baton_challenge.dart

@@ -0,0 +1,100 @@
+import 'package:flutter/material.dart';
+import 'package:the_nature_of_code/chapters/three_oscillation/mover.dart';
+
+class BatonOscillation extends StatefulWidget {
+  const BatonOscillation({super.key});
+
+  @override
+  State<BatonOscillation> createState() => _BatonOscillationState();
+}
+
+class _BatonOscillationState extends State<BatonOscillation>
+    with SingleTickerProviderStateMixin {
+  late AnimationController controller;
+
+  Mover? mover;
+
+  @override
+  void initState() {
+    super.initState();
+    controller = AnimationController(
+      vsync: this,
+      duration: const Duration(milliseconds: 100),
+    )..repeat();
+
+    controller.addListener(() {
+      setState(() {
+        mover?.update();
+      });
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return LayoutBuilder(
+      builder: (context, constraints) {
+        mover ??= Mover(constraints.biggest);
+        return Center(
+          child: Transform.rotate(
+            angle: mover?.angle ?? 0,
+            child: _box(80),
+          ),
+        );
+      },
+    );
+  }
+
+  Widget _box(double size) {
+    return Container(
+      width: size,
+      height: size,
+      color: Colors.red,
+    );
+  }
+}
+
+class BatonPainter extends CustomPainter {
+  final double angle;
+
+  const BatonPainter(this.angle);
+
+  @override
+  void paint(Canvas canvas, Size size) {
+    canvas.translate(size.width / 2, size.height / 2);
+    canvas.rotate(angle);
+
+    const center =
+        Offset(0, 0); // center is zero offset since origin is now at the center
+    const halfOfLengthOffset = Offset(80, 0);
+    canvas.drawLine(
+      center - halfOfLengthOffset,
+      center + halfOfLengthOffset, // length of 120
+      Paint()
+        ..color = Colors.green
+        ..strokeWidth = 3,
+    );
+
+    canvas.drawCircle(
+      center - halfOfLengthOffset,
+      16,
+      Paint()
+        ..color = Colors.blue
+        ..strokeWidth = 2,
+    );
+    canvas.drawCircle(
+      center + halfOfLengthOffset,
+      16,
+      Paint()
+        ..color = Colors.blue
+        ..strokeWidth = 2,
+    );
+  }
+
+  @override
+  bool shouldRepaint(covariant CustomPainter oldDelegate) {
+    if (oldDelegate is! BatonPainter) return false;
+
+    if (oldDelegate.angle != angle) return true;
+    return false;
+  }
+}