So, the guys on the coding side told me to drop by here with this...
I am rendering a world using LWJGL, and what I need to find out are the x, y and z coordinates of the block that the player clicks on their screen. Player position in all three dimensions is known, as is the camera distance and angle, both relative to ground and to the player's orientation. Screen width and height are known, and the mouse x and y coordinates are called when the player clicks. The size of each block/cube used as a part of the 3D world is relative to the screen's size.
Thanks for your help.
Edit: Uhm... trying to pose this question more mathematically just made me realize that I just can't. I'll try and go ask on the coding side again.