Erwan's Blog

Farseer has one specific not always easy to deal with : your world is meant in KMS (kilo meter second) whereas your rendering is in pixel.
Added to that, your world and rendering are two complete different things which does not make it easy to debug.

This where the DebugViewXNA class kicks in : it will render your world 🙂
This and a few other things like stats, datas, etc.

The how to use the DebugViewXNA class is rather easy :

–add the project reference to debugview.xna.dll
–add an imports to FarseerPhysics.DebugView
–declare a _debugView As DebugViewXNA
–set it up in loadcontent (for instance) :

_debugView = New DebugViewXNA(world)
_debugView.AppendFlags(DebugViewFlags.DebugPanel)
_debugView.DebugPanelPosition = New Vector2(15, 15)
_debugView.DefaultShapeColor = Color.White
_debugView.SleepingShapeColor = Color.LightGray
_debugView.LoadContent(GraphicsDevice, Content)

-use it in your draw method (after your spritebatch.end) :

Dim projection As Matrix = Matrix.CreateOrthographicOffCenter(0.0F, graphics.GraphicsDevice.Viewport.Width * DrawablePhysicsObject.pixelToUnit, graphics.GraphicsDevice.Viewport.Height * DrawablePhysicsObject.pixelToUnit, 0.0F, 0.0F, 1.0F)
_debugView.RenderDebugDataVB(projection)


A video to illustrate switching between rendering and debugging.

In previous article, I have regularly used either a rotating sprite (a car, a rocket, a tank, etc) OR an animated sprite (a walking character).

Here below these 2 classes.
You can use them in as a quick start for a game so that you dont have to bother with this part.

To use it the animated class :
–declare it Dim animated As Animated
–load it animated = New Animated(mTexture, 1, position, 0, 28, 32)
–update it animated.Update(position, direction_)
–draw it animated.Draw(spriteBatch)

Same goes with the rotating class :
–declare it Dim rotated As rotated
–load it rotated = New rotated(texture, _scale, New Vector2(50, 50), New Vector2(0, 0), _rotation, _speed)
–update it rotated.Update(_rotation, _speed)
–draw it rotated.Draw(SpriteBatch)

The animated class here : clsRotated .
The rotating class here : clsAnimated .

In Article 16, we had animated a sprite.
Now lets enhance the demo with a 2d camera following our character creating a simple scrolling effect.
Note : a next article will cover parallax scrolling.

We will simply had a camera class.
Lets declare our camera,
then instantiate it in loadcontent passing the width and height,

cam = New camera(graphics.GraphicsDevice.Viewport.Width, graphics.GraphicsDevice.Viewport.Height)

update it,

cam.setfocalpoint(New Vector2(dest_box.X, dest_box.Y), New Vector2(graphics.PreferredBackBufferWidth * 1.5 + 32, graphics.PreferredBackBufferHeight * 1.5 + 32))
cam.update()

and finally use it in our draw method thru a parameter in the spritebatch.begin method

spriteBatch.Begin(SpriteSortMode.Immediate, BlendState.AlphaBlend, Nothing, Nothing, Nothing, Nothing, cam.viewmatrix)


The camera class is itself extremely simple (note that we will manage zoom and rotation also later)

Imports Microsoft.Xna.Framework
Public Class camera
Public position As Vector2
Public viewmatrix As Matrix
Dim _screenx As Integer
Dim _screeny As Integer
Public Sub New(SizeX As Integer, sizeY As Integer)
_screenx = SizeX
_screeny = sizeY
End Sub

If position.X < 0 Then position.X = 0 If position.Y < 0 Then position.Y = 0 End Sub Public Sub update() viewmatrix = Matrix.CreateTranslation(New Vector3(-position, 0)) End Sub End Class

The video illustrating this.

The source code.
xna_demo_23.2