c# - Camera offest when following body -

when moving object around, camera doesn't remain centered on object.

i can't seem locate bug. please help.

initial-

`convertunits.todisplayunits(body.position)-(camera._screencenter- camera._cameraposition)` 

this returns zero.

after movement changes.

i using farseer physics engine 3.5 , moving body using force.

body.applyforce(); 

this camera class-

class camera     {         private static matrix _view;         public static vector2 _cameraposition;         public static vector2 _screencenter;         private static float _zoom;         private static float _rotation;          public static void load(graphicsdevicemanager _graphics)         {             _view = matrix.identity;             _cameraposition = vector2.zero;             _screencenter = new vector2(_graphics.graphicsdevice.viewport.width / 2f, _graphics.graphicsdevice.viewport.height / 2f);             _rotation = 0f;             _zoom = 1.0f;         }          public static void handleinput(keyboardstate state)         {             if (state.iskeydown(keys.add) && _zoom < 1.0f)                 _zoom += 0.1f;             if (state.iskeydown(keys.subtract) && _zoom > 0.1f)                 _zoom -= 0.1f;              update();         }          public static void update()         {             _view = matrix.createtranslation(                                         new vector3(_cameraposition - _screencenter, 0f)) *                                          matrix.createrotationz(_rotation) *                                          matrix.createscale(new vector3(_zoom, _zoom, 1)) *                                          matrix.createtranslation(new vector3(_screencenter, 0f));         }          public static void follow(body body)         {             if (body != null)                 _cameraposition = _screencenter - convertunits.todisplayunits(body.position);         }          public static matrix getview()         {             return _view;         }     } 

your _screencenter origin of camera, , not being calculated correctly when make matrix.

try:

        return matrix.createtranslation(new vector3(-position, 0.0f)) *                matrix.createtranslation(new vector3(-origin, 0.0f)) *                matrix.createrotationz(rotation) *                matrix.createscale(zoom, zoom, 1) *                matrix.createtranslation(new vector3(origin, 0.0f));