intersection mouse ray and polygon

[jakovn]

Hi everybody! I am new to game programming so this must be a basic question for you

 

What is the easyest way (and fastest for computing) to achieve this using DX or other way:

 

I have known camera position and a simple polygon defined by 3 vertex in space, how do I get xyz position where mouse intersects this polygon?

 

I want the most accurate method

 

Thanks