Adds sprite physics groups

packages/flutter_sprites/lib/flutter_sprites.dart

@@ -35,6 +35,7 @@ part 'src/node_with_size.dart';
 part 'src/particle_system.dart';
 part 'src/physics_body.dart';
 part 'src/physics_debug.dart';
+part 'src/physics_group.dart';
 part 'src/physics_joint.dart';
 part 'src/physics_shape.dart';
 part 'src/physics_world.dart';

packages/flutter_sprites/lib/src/node.dart

@@ -132,9 +132,8 @@ class Node {
   void set rotation(double rotation) {
     assert(rotation != null);
 
-    if (_physicsBody != null && parent is PhysicsWorld) {
-      PhysicsWorld physicsNode = parent;
-      physicsNode._updateRotation(this.physicsBody, rotation);
+    if (_physicsBody != null && (parent is PhysicsWorld || parent is PhysicsGroup)) {
+      _updatePhysicsRotation(physicsBody, rotation, parent);
       return;
     }
 
@@ -142,6 +141,19 @@ class Node {
     invalidateTransformMatrix();
   }
 
+  void _updatePhysicsRotation(PhysicsBody body, double rotation, Node physicsParent) {
+    if (physicsParent == null) return;
+
+    if (physicsParent is PhysicsWorld) {
+      PhysicsWorld world = physicsParent;
+      world._updateRotation(body, rotation);
+    } else if (physicsParent is PhysicsGroup) {
+      _updatePhysicsRotation(body, rotation + physicsParent.rotation, physicsParent.parent);
+    } else {
+      assert(false);
+    }
+  }
+
   void _setRotationFromPhysics(double rotation) {
     assert(rotation != null);
     _rotation = rotation;
@@ -166,9 +178,8 @@ class Node {
   void set position(Point position) {
     assert(position != null);
 
-    if (_physicsBody != null && parent is PhysicsWorld) {
-      PhysicsWorld physicsNode = parent;
-      physicsNode._updatePosition(this.physicsBody, position);
+    if (_physicsBody != null && (parent is PhysicsWorld || parent is PhysicsGroup)) {
+      _updatePhysicsPosition(this.physicsBody, position, parent);
       return;
     }
 
@@ -176,6 +187,20 @@ class Node {
     invalidateTransformMatrix();
   }
 
+  void _updatePhysicsPosition(PhysicsBody body, Point position, Node physicsParent) {
+    if (physicsParent == null) return;
+
+    if (physicsParent is PhysicsWorld) {
+      PhysicsWorld world = physicsParent;
+      world._updatePosition(body, position);
+    } else if (physicsParent is PhysicsGroup) {
+      Vector4 parentPos = physicsParent.transformMatrix.transform(new Vector4(position.x, position.y, 0.0, 1.0));
+      _updatePhysicsPosition(body, new Point(parentPos.x, parentPos.y), physicsParent.parent);
+    } else {
+      assert(false);
+    }
+  }
+
   void _setPositionFromPhysics(Point position) {
     assert(position != null);
     _position = position;
@@ -310,6 +335,7 @@ class Node {
   void addChild(Node child) {
     assert(child != null);
     assert(child._parent == null);
+    assert(!(child is PhysicsGroup) || this is PhysicsGroup || this is PhysicsWorld);
 
     _childrenNeedSorting = true;
     _children.add(child);
@@ -318,6 +344,10 @@ class Node {
     _childrenLastAddedOrder += 1;
     child._addedOrder = _childrenLastAddedOrder;
     if (_spriteBox != null) _spriteBox._registerNode(child);
+
+    if (child is PhysicsGroup) {
+      child._attachGroup(child, child._world);
+    }
   }
 
   /// Removes a child from this node.
@@ -330,6 +360,10 @@ class Node {
       child._spriteBox = null;
       if (_spriteBox != null) _spriteBox._deregisterNode(child);
     }
+
+    if (child is PhysicsGroup) {
+      child._detachGroup(child);
+    }
   }
 
   /// Removes this node from its parent node.

packages/flutter_sprites/lib/src/physics_group.dart

+part of flutter_sprites;
+
+class PhysicsGroup extends Node {
+
+  set scaleX(double scaleX) {
+    assert(false);
+  }
+
+  set scaleY(double scaleX) {
+    assert(false);
+  }
+
+  set skewX(double scaleX) {
+    assert(false);
+  }
+
+  set skewY(double scaleX) {
+    assert(false);
+  }
+
+  set physicsBody(PhysicsBody body) {
+    assert(false);
+  }
+
+  set position(Point position) {
+    super.position = position;
+    _invalidatePhysicsBodies(this);
+  }
+
+  set rotation(double rotation) {
+    super.rotation = rotation;
+    _invalidatePhysicsBodies(this);
+  }
+
+  set scale(double scale) {
+    super.scale = scale;
+    _invalidatePhysicsBodies(this);
+  }
+
+  void _invalidatePhysicsBodies(Node node) {
+    if (_world == null) return;
+
+    if (node.physicsBody != null) {
+      // TODO: Add to list
+      _world._bodiesScheduledForUpdate.add(node.physicsBody);
+    }
+
+    for (Node child in node.children) {
+      _invalidatePhysicsBodies(child);
+    }
+  }
+
+  void addChild(Node node) {
+    super.addChild(node);
+
+    PhysicsWorld world = _world;
+    if (node.physicsBody != null && world != null) {
+      node.physicsBody._attach(world, node);
+    }
+
+    if (node is PhysicsGroup) {
+      _attachGroup(this, world);
+    }
+  }
+
+  void _attachGroup(PhysicsGroup group, PhysicsWorld world) {
+    for (Node child in group.children) {
+      if (child is PhysicsGroup) {
+        _attachGroup(child, world);
+      } else if (child.physicsBody != null) {
+        child.physicsBody._attach(world, child);
+      }
+    }
+  }
+
+  void removeChild(Node node) {
+    super.removeChild(node);
+
+    if (node.physicsBody != null) {
+      node.physicsBody._detach();
+    }
+
+    if (node is PhysicsGroup) {
+      _detachGroup(this);
+    }
+  }
+
+  void _detachGroup(PhysicsGroup group) {
+    for (Node child in group.children) {
+      if (child is PhysicsGroup) {
+        _detachGroup(child);
+      } else if (child.physicsBody != null) {
+        child.physicsBody._detach();
+      }
+    }
+  }
+
+  PhysicsWorld get _world {
+    if (this.parent is PhysicsWorld)
+      return this.parent;
+    if (this.parent is PhysicsGroup) {
+      PhysicsGroup group = this.parent;
+      return group._world;
+    }
+    return null;
+  }
+}

packages/flutter_sprites/lib/src/physics_world.dart

@@ -43,6 +43,8 @@ class PhysicsWorld extends Node {
 
   List<box2d.Body> _bodiesScheduledForDestruction = [];
 
+  List<PhysicsBody> _bodiesScheduledForUpdate = [];
+
   _PhysicsDebugDraw _debugDraw;
 
   double b2WorldToNodeConversionFactor = 10.0;
@@ -71,6 +73,14 @@ class PhysicsWorld extends Node {
   }
 
   void _stepPhysics(double dt) {
+    // Update transformations of bodies whose groups have moved
+    for (PhysicsBody body in _bodiesScheduledForUpdate) {
+      Node node = body._node;
+      node._updatePhysicsPosition(body, node.position, node.parent);
+      node._updatePhysicsRotation(body, node.rotation, node.parent);
+    }
+    _bodiesScheduledForUpdate.clear();
+
     // Remove bodies that were marked for destruction during the update phase
     _removeBodiesScheduledForDestruction();