How to find correct offset to adjust sprite to the position of box2D body after rotation

Vote count:

0

I am trying to implement phsyics with the as3 box2d port. I currently have a b2body for each of some certain sprites in my game and I am able to update the sprite's positions correctly from the positions of the bodies. This is shown in the picture below (debugDraw shows the positions of the b2bodies overlaid on their corresponding spirtes. The green rectangles are the walls and floor)

However, I also want to have the sprite's rotations reflect the rotations of the b2bodies. But, after I rotate the sprites, the offset I use to center them correctly with the b2body positions is no longer accurate.

My code for updating the sprites positions is as follows:

private function Update(update_event:TimerEvent):void
            {
                //step physics simulation forward 
                world.Step(0.025,10,10);



                //update all objects in world
                for each (var obj:HouseItemPhysicsObject in physicsObjects)
                {
                    //update object's position from gravity if it is not being dragged
                    if(!obj.isHeld)
                    {
                        /*adjust rotation of sprite along with body -> yourMC.rotation = (yourMCbody.GetAngle() * 180 / Math.PI) % 360; */
                        obj.object.rotation = (obj.pBody.GetAngle() * 180/Math.PI) % 360;   

                        if(obj.object.rotation >=5)
                        // set object's x position but adjust for offset between the cooridinate systems
                        obj.x = (obj.pBody.GetPosition().x* scaleFactor)-(obj.object.width/2); 
                        //keep in horizontal bounds of screen
                        if(obj.x > GeneralConstants.GAME_WIDTH)
                        {
                            obj.x =GeneralConstants.GAME_WIDTH;
                        }
                        else if(obj.x < 0)
                        {
                            obj.x = 0;
                        }

                        // set object's x position but adjust for offset between the cooridinate systems in Flash and box2d
                        obj.y = (obj.pBody.GetPosition().y * scaleFactor)-(obj.object.height/2);

                        //keep in vertical bounds of the screen
                        if(obj.y > GeneralConstants.GAME_HEIGHT)
                        {
                            obj.y =GeneralConstants.GAME_HEIGHT;
                        }
                        else if(obj.x < 0)
                        {
                            obj.x = 0;
                        }



                        /*Draw shapes to see for debug*/
                        //obj.DrawDebug();
                        //trace("OBJECT's X is :" + obj.x + " Y is :" +obj.y);
                        trace("Object's rotation is:" + obj.object.rotation);
                    }



                }

                //move debug draw to front of display list
                m_sprite.parent.setChildIndex(m_sprite, m_sprite.parent.numChildren - 5);
                world.DrawDebugData();
            }

How can I find the correct X and Y offset between the coordinate systems (Flash and Box2d) after rotating the sprite according to the b2Body? Thanks for the help.

asked 47 secs ago

Christian

482