This one is a pickle. Basically, I am trying to keep a 3D object in the center of the camera. I figured the easy way would be to invert the view matrix, add 5 to the mat.Forward member and everything would be O.K. Well, now I don't even see it. My previous attempts were fiddling with the UpDown / LeftRight rotations, they worked for the most part but couldn't get it corrected without really hardcoding the issue (and even then didn't work properly). Been stuck on this for the past 3 or 4 days, really not much else I can think of.

if( nType != EItemType.None )
{
    Matrix matWorld = Matrix.Invert( m_Player.m_Camera.View );
    matWorld.Translation += (matWorld.Forward * 5);

    m_Effect.World = matWorld;
    m_Effect.View = m_Player.m_Camera.View;
    m_Effect.Projection = m_Player.m_Camera.Projection;
    m_Effect.TextureEnabled = true;
    m_Effect.Texture = m_Texture;

    foreach( EffectPass pass in m_Effect.CurrentTechnique.Passes ) 
    {
        pass.Apply();

        m_GraphicsDevice.BlendState = BlendState.AlphaBlend;

        m_GraphicsDevice.DrawUserPrimitives<VertexPositionTexture>( PrimitiveType.TriangleList,    m_Verts.ToArray(), 0, 2 );

    }
}

-Edit- For the most part, this works:

Matrix matWorld = Matrix.Identity *
					Matrix.CreateScale( 2f ) *
					Matrix.CreateRotationZ( -m_Player.m_Camera.UpDownRot ) *
					Matrix.CreateRotationY( m_Player.m_Camera.LeftRightRot - MathHelper.PiOver2 ) *
					Matrix.CreateTranslation( m_Player.Position + (m_Player.LookVector * 0.3f) );

I thought I introduced tearing, but nope. Was able to angle my camera just right and noticed it was my item. Fixed!

One of the first few things I tried, perhaps I made a mistake on that particular one.. I'll give that a go again.

What bugs me is that the most obvious solutions seems to work, just not as expected, eg;

                Matrix matWorld = Matrix.Identity *
                    Matrix.CreateTranslation( m_Player.Position + m_Player.LookVector );

		m_Effect.World = matWorld;
		m_Effect.View = m_Player.m_Camera.View;
		m_Effect.Projection = m_Player.m_Camera.Projection;
		m_Effect.TextureEnabled = true;
		m_Effect.Texture = m_Texture; 

Don't mean to bump/spam/others..

Still haven't quite figured it out, but have found a resource to get this going. Seems pretty solid for anyone looking to do the above.

Needs some tweaks for my purpose, but does make good use of quaternion's (one thing I really need to switch to!).

http://www.dhpoware.com/demos/xnaFirstPersonCamera.html

I'd do something like this:

- when camera moves

- the object you want to keep static to camera -> worldpos = camerapos

- camerapos.z -= 5 or += 5?

Tried. I figured something out new.. Well, observed. I imported a model that was designed in 3DWings into my content solution, redid my method and bam, it worked.

It appears I'm missing something (duh!) that the imported model has, that my coded model doesn't. I'm explaining what I've done below, but before I do, please note that I am still new to 3D and my code may not be completely efficient, the second is temporarily :]

I have a tilesheet of textures, used for the UV coordinates. I'm essentially taking the coordinates from the UV and building a array of VertexPositionTexture for the model:

VertexBuilder.BuildVertexFromUV

public static List<VertexPositionTexture> BuildVertexFromUV( Vector3 vecPosition, Vector2[] vecUV )
{
	List<VertexPositionTexture> ret = new List<VertexPositionTexture>();

	foreach( Vector2 uv in vecUV )
		ret.Add( new VertexPositionTexture( vecPosition + new Vector3(uv.X, uv.Y, 0), uv ) );

	return ret;
}

ItemRender.OnChangeItemInHand

public void OnChangeItemInHand( EItemType nType )
{
	if( nType != m_nItemHold )
	{
		m_Verts.Clear();

		m_Verts = BlockVertexBuilder.BuildVertexFromUV( new Vector3(0, 0, 0),
		new Vector3( 1, 0, 2 ),
		ItemTexture.m_UVMappings[(int)nType] );

		m_VB = new VertexBuffer( m_GraphicsDevice, typeof(VertexPositionTexture), m_Verts.Count, BufferUsage.WriteOnly );
		m_VB.SetData( m_Verts.ToArray() );

		m_nItemHold = nType;
	}
}

Again, all fine and dandy. Now, the glorified issue.

ItemRender.RenderItemInHand

public void RenderItemInHand( GameTime gameTime )
{
	EItemType nType = m_Player.PlayerInventory.GetHoldingItemType();
	OnChangeItemInHand( nType ); //Remember, temporarily :]

	if( nType != EItemType.None )
	{
		Matrix matWorld = Matrix.CreateScale( 2f ) *
			Matrix.CreateRotationX( fWeaponRotX ) *
			Matrix.CreateRotationY( fWeaponRotY ) *
			Matrix.CreateRotationZ( fWeaponRotZ ) *
			Matrix.CreateTranslation( vecWeaponRot ) *
			Matrix.CreateRotationZ( -m_Player.m_Camera.UpDownRot ) *
			Matrix.CreateRotationY( m_Player.m_Camera.LeftRightRot - MathHelper.PiOver2 ) *
			Matrix.CreateTranslation( m_Player.Position + (m_Player.LookVector * 0.3f) );

		m_Effect.World = matWorld;
		m_Effect.View = m_Player.m_Camera.View;
		m_Effect.Projection = m_Player.m_Camera.Projection;
		m_Effect.TextureEnabled = true;
		m_Effect.Texture = m_Texture;

		foreach( EffectPass pass in m_Effect.CurrentTechnique.Passes ) 
		{
			pass.Apply();

			m_GraphicsDevice.BlendState = BlendState.AlphaBlend;

			m_GraphicsDevice.DrawUserPrimitives<VertexPositionTexture>( PrimitiveType.TriangleList, m_Verts.ToArray(), 0, 2 );
		}
	}
}
//Values in the rotation/translation above:

If anyone has any idea, please. In the mean time, I am going to write a small debugger for this so I can check what's happening in-game quicker and easier.

(P.S: I know this question has been posted A LOT on these forums, I have searched.. For days. So I apologize for the repetitiveness!)