Animer "bones" d'un modèle

Bonjour j'essaie d'animer un bones du personnage "dude" fournit dans les exemples de XNA.

Je copie soigneusement le code mais rien n'y fait cela ne marche pas xD!!

Code:

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//declaration
 
        ModelBone leftThigh;
        Matrix leftThighTransform;
        public Matrix matRot = Matrix.Identity;
 
//affectation
 
            this.leftThigh = model.Bones["L_UpperArm"];
            this.leftThighTransform = leftThigh.Transform;
 
//draw
 
        public override void Draw(GameTime gameTime)
        {
            //Notice that the entity's worldTransform property is being accessed here.
            //This property is returns a rigid transformation representing the orientation
            //and translation of the entity combined.
            //There are a variety of properties available in the entity, try looking around
            //in the list to familiarize yourself with it.
 
            leftThigh.Transform = matRot * leftThighTransform;
            Matrix[] boneTransforms = new Matrix[model.Bones.Count];
            model.CopyAbsoluteBoneTransformsTo(boneTransforms);
 
            worldMatrix = transform * entity.worldTransform;
 
            model.CopyAbsoluteBoneTransformsTo(boneTransforms);
            foreach (ModelMesh mesh in model.Meshes)
            {
                foreach (BasicEffect effect in mesh.Effects)
                {
                    effect.World = boneTransforms[mesh.ParentBone.Index] * worldMatrix;
                    effect.View = (Game as RunMan).user.camera.ViewMatrix;
                    effect.Projection = (Game as RunMan).user.camera.projectionMatrix;
                }
                mesh.Draw();
            }
            base.Draw(gameTime);
        }
 
//changeable
 
            if (keyboardState.IsKeyDown(Keys.Up))
            {
                camera.MoveForward(dt);
                //game.entModelHero.entity.linearVelocity = Vector3.Forward * 5;
                game.entModelHero.matRot += Matrix.CreateRotationZ(0.3f);
            }

Si quelqu'un à une idée , je suis preneur !

Merci & bonnes fêtes!