XNA Tile from Screen Location

Question

I have a tile based game that is in a semi-isometric view created by a transformation. The tiles are created by a Texture2d rendered on a 3d surface.

I am using the following code for transformation:

View = Matrix.CreateLookAt(new Vector3(0, -1.1f, 1.6f), new Vector3(0, 0, 0), new Vector3(0, 53, 0));
Projection = Matrix.CreatePerspectiveFieldOfView(MathHelper.Pi - 2.4f, 4.0f / 3.0f, 1, 500);

quadEffect = new BasicEffect(device);

quadEffect.World = Matrix.Identity;
quadEffect.View = View;
quadEffect.Projection = Projection;
quadEffect.TextureEnabled = true;

quad = new Quad(new Vector3(0, 0, 0), Vector3.Backward, Vector3.Up, 3, 3);

My problem comes along when I attempt to get the current tile that I am hovering the mouse over. I have a mouse X and Y however I can't seem to figure out how to transform these screen coordinates into a tile X and Y. The tiles are 128px by 128px; however, after the camera transformation they are smaller on the top and larger on the bottom(to create the isometric view)

I've tried transforming the mouse X and Y with the same projection matrix. However, this didn't work. I think it is due to the view matrix not being taken into account... sample below:

Vector3.Transform(new Vector3(Mouse.GetState().X, Mouse.GetState().Y, 0), Projection);

This image may provide more information... is also shows the hours I've put into figuring this out:

Answer 1

You can use Viewport.UnProject with two source values:

A(MouseX, MouseY, 0) B(MouseX, MouseY, 1)

You will get the two unprojects points that can be used to get a ray, then you have to get the ray intersection with the plane where are the tiles.

http://msdn.microsoft.com/en-us/library/microsoft.xna.framework.graphics.viewport.unproject.aspx