Added accessors for a Body's velocity_func and position_func.

lib/chipmunk-ffi/body.rb

@@ -5,8 +5,8 @@ module CP
 
   class BodyStruct < NiceFFI::Struct
     layout(
-      :bodyVelocityFunc, :cpBodyVelocityFunc,
-      :bodyPositionFunc, :cpBodyPositionFunc,
+      :velocity_func, :cpBodyVelocityFunc,
+      :position_func, :cpBodyPositionFunc,
       :m, CP_FLOAT,
       :m_inv, CP_FLOAT,
       :i, CP_FLOAT,
@@ -54,9 +54,12 @@ def initialize(*args)
       when 2
         ptr = CP.cpBodyNew(*args)
         @struct = BodyStruct.new ptr
+        set_data_pointer
       else
         raise "wrong number of args for Body, got #{args.size}, but expected 2"
       end
+      set_default_velocity_lambda
+      set_default_position_lambda
     end
 
     def m
@@ -194,5 +197,60 @@ def update_position(dt)
       CP.cpBodyUpdatePosition(@struct.pointer,dt)
     end
 
+    def velocity_func
+      @user_level_velocity_lambda
+    end
+
+    def velocity_func=(l)
+      @user_level_velocity_lambda = l
+
+      # We keep the lambda in an ivar to keep it from being GCed
+      @body_velocity_lambda = Proc.new do |body_ptr,g,dmp,dt|
+        body_struct = BodyStruct.new(body_ptr)
+        obj_id = body_struct.data.get_long(0)
+        body = ObjectSpace._id2ref(obj_id)
+        l.call(body,g,dmp,dt)
+      end
+      @struct.velocity_func = @body_velocity_lambda
+    end
+
+    def position_func
+      @user_level_position_lambda
+    end
+
+    def position_func=(l)
+      @user_level_position_lambda = l
+
+      # We keep the lambda in an ivar to keep it from being GCed
+      @body_position_lambda = Proc.new do |body_ptr,dt|
+        body_struct = BodyStruct.new(body_ptr)
+        obj_id = body_struct.data.get_long(0)
+        body = ObjectSpace._id2ref(obj_id)
+        l.call(body,dt)
+      end
+      @struct.position_func = @body_position_lambda
+    end
+
+    private
+    def set_data_pointer
+      mem = FFI::MemoryPointer.new(:long)
+      mem.put_long 0, object_id
+      # this is needed to prevent data corruption by GC
+      @body_pointer = mem
+      @struct.data = mem
+    end
+
+    def set_default_velocity_lambda
+      @user_level_velocity_lambda = Proc.new do |body,g,dmp,dt|
+        body.update_velocity(g,dmp,dt)
+      end
+    end
+
+    def set_default_position_lambda
+      @user_level_position_lambda = Proc.new do |body,dt|
+        body.update_position(dt)
+      end
+    end
+
   end
 end

spec/body_spec.rb

@@ -152,5 +152,49 @@
     b.v.x.should be_close(0.1,0.001)
     b.v.y.should be_close(0,0.001)
   end
+
+  it 'can get its velocity function' do
+    b = CP::Body.new(5, 7)
+    b.apply_impulse(vec2(1,0), ZERO_VEC_2)
+    b.velocity_func.call(b,vec2(0,0), 0.5, 25)
+    b.v.x.should be_close(0.1,0.001)
+    b.v.y.should be_close(0,0.001)
+  end
+
+  it 'can set its velocity function' do
+    b = CP::Body.new(5, 7)
+
+    b.velocity_func = Proc.new do |body,gravity,damping,dt|
+      d = body.p - vec2(5,5)
+      g = (d * (-500.0/(d.dot(d))))
+      body.update_velocity(g,damping,dt)
+    end
+
+    b.velocity_func.call(b,ZERO_VEC_2,0.5,25)
+    b.v.x.should be_close(1250.0,10)
+    b.v.y.should be_close(1250.0,10)
+
+  end
+
+  it 'can get its position function' do
+    b = CP::Body.new(5, 7)
+    b.apply_impulse(vec2(1,0), ZERO_VEC_2)
+    b.position_func.call(b,25)
+    b.p.x.should be_close(5,0.001)
+    b.p.y.should be_close(0,0.001)
+  end
+
+  it 'can set its position function' do
+    b = CP::Body.new(5,7)
+
+    b.position_func = Proc.new do |body,dt|
+      body.p = vec2(5,5)
+    end
+
+    b.position_func.call(b,25)
+    b.p.should == vec2(5,5)
+  end
+
+
 
 end