Xna model parts are overlying others

Question

I am trying to import in XNA an .fbx model exported with blender.

Here is my drawing code

public void Draw()
{
    Matrix[] modelTransforms = new Matrix[Model.Bones.Count];
    Model.CopyAbsoluteBoneTransformsTo(modelTransforms);

    foreach (ModelMesh mesh in Model.Meshes)
    {
        foreach (BasicEffect be in mesh.Effects)
        {
            be.EnableDefaultLighting();
            be.World = modelTransforms[mesh.ParentBone.Index] * GameCamera.World * Translation;
            be.View = GameCamera.View;
            be.Projection = GameCamera.Projection;
        }
        mesh.Draw();
    }
}

The problem is that when I start the game some model parts are overlying others instead of being behind. I've tried to download other models from internet but they have the same problem.

Answer 1

Your device states are probably wrong. This often happens when mixing 2D and 3D (for example the overload for SpriteBatch.Begin() which takes no arguments sets some device states that are incompatible with 3D rendering. No worries though, all you have to do is to make sure that the following device states are set the way you want them:

BlendState, SamplerState, DepthStencilState, RasterizerState

The default values, which should be fine for just rendering a model are:

GraphicsDevice.BlendState = BlendState.Opaque;
GraphicsDevice.DepthStencilState = DepthStencilState.Default;
GraphicsDevice.RasterizerState = RasterizerState.CullCounterClockwise;
GraphicsDevice.SamplerStates[0] = SamplerState.LinearWrap;

Especially take a look at DepthStencilState it should be set to DepthStencilState.Default and at the moment is probably set to DepthStencilState.None.

To learn more about graphics device states take a look at this series of "What is" articles on MSDN. To learn more about why this is managed in such a way you should read this article by Shawn Hargreaves (used to be on the XNA team and his blog posts are all brilliant)