Multiplying mouse position vector by model view projection matrix

[squishybanana]

I've recently started working on a game engine for java using lwjgl. I created vector and matrix classes that I can multiply. I want to check if the mouse is within a certain range in world space even though glfw gives me the pixel it's on. The problem is that opengl uses 4 dimensions and the mouse is 2 dimensions. I know that the fourth dimension represents perspective but I don't know how I should multiply this.

How does the modelview projection matrix store information?

[Kai]

What you want is called "unprojecting". You want to unproject window coordinates to world coordinates.
Google for "OpenGL unproject", and you'll find a lot of resources explaining this.