Why does my model render differently with different BasicEffect instances?

Question

I'd like to understand why I get a completely different result when I replace the effects of a model (as suggested by How To: Draw a Model with a Custom Effect) with a BasicEffect that I instantiate myself:

var basicEffect = new BasicEffect( game.GraphicsDevice );
basicEffect.EnableDefaultLighting();
foreach (var mesh in _modelHead.Meshes)
    foreach (var part in mesh.MeshParts)
        part.Effect = basicEffect;

My goal is of course to use an effect of my own later, but for the moment I'd really like to understand what's going on!? What is different with the predefined BasicEffect from the one I instantiate myself? When I inspect the properties of the two instances they seem to be all the same.

1. How it looks with the "default" BasicEffect
2. How it looks when I instantiate a new BasicEffect

Answer 1

The model file contains data about materials, in this case it looks like the diffuse color or texture. When you create a new BasicEffect object it doesn't contain the right colors and such, so you get white.

See here:

http://msdn.microsoft.com/en-us/library/microsoft.xna.framework.graphics.basiceffect.diffusecolor.aspx

http://msdn.microsoft.com/en-us/library/microsoft.xna.framework.graphics.basiceffect.texture.aspx

If you want to use the same texture, you can do this (I haven't tested though):

foreach (var mesh in _modelHead.Meshes)
{
    foreach (var part in mesh.MeshParts)
    {
        var specificEffect = new BasicEffect(game.GraphicsDevice);
        specificEffect.EnableDefaultLighting();
        specificEffect.Texture = ((BasicEffect)part.Effect).Texture;
        specificEffect.DiffuseColor = ((BasicEffect)part.Effect).DiffuseColor;
        part.Effect = specificEffect;
    }
}

Obviously this code can be optimized a lot as it becomes redundant after the first call.

EDIT:

Just to explain why the properties seem the same, once your code runs once the effects become the same, so if you're seeing anything but the first call the properties will be the same.