Return values
The function returns the current mouse position in xpos and ypos.

Description
The function returns the current mouse position. If the cursor is not hidden, the mouse position is the
cursor position, relative to the upper left corner of the window and limited to the client area of the
window. If the cursor is hidden, the mouse position is a virtual absolute position, not limited to any
boundaries except to those implied by the maximum number that can be represented by a signed integer
(normally -2147483648 to +2147483647).

Notes
A window must be opened for the function to have any effect, and glfwPollEvents, glfwWaitEvents or
glfwSwapBuffers must be called before any mouse movements are recorded and reported by
glfwGetMousePos.