This extension uses the Pointer Lock API to lock the cursor to the game screen when the game window is clicked, and retrieves the mouse changes once the mouse is locked. The included functions are:
mouse_x_change() - Returns the number of pixels the mouse has moved on the x-axis.
mouse_y_change() - Returns the number of pixels the mouse has moved on the y-axis.
clear_change() - Called after either mouse_x_change() or mouse_y_change() to reset them back to 0.
The download includes an HTML5 first person demo and the .gmez extension.