2D mouse coordinates from 3d object projection

Question

Not entirely certain of the nomenclature here -- basically, after placing a model in world coordinates and setting up a 3D camera to look at it the model has been projected onto the screen in a 2D fashion.

What I'd like to do is determine if the mouse is inside the projected view of the model.

Is there a way to "unproject" in the XNA framework? Or what is this process called as, so that I can better search for it?

Answer 1

I can suggest a method i use

First of all, you must create a ray that represents your mouse position in 3d space

vector3 near = new vector3(mouse.x,mouse.y,0);
vector3 far = new vector3(mouse.x,moue.y,1);

near GraphicsDevive.Viewport.Unproject(near,view,projection,world);
near GraphicsDevive.Viewport.Unproject(far,view,projection,world);

matrix world must be inverse of your models world matrix.

vector3 direction = far - near;
Ray ray = (near,direction);

the test this ray for collision with models bounding sphere.

I demand excude for this arbitrary answer that can't be pasted in your project, but im little bit lazy to consult references.

UPDATE. http://xbox.create.msdn.com/en-US/education/catalog/sample/picking_triangle Here is an accurate example of model picking. It is more accurate than mine, but it involves ModelProcessor modifying.