Name

XCreateMouseVoid

Creates an undecorated black window and prevents the mouse from entering that window.

Syntax

XCreateMouseVoid x y w h [mode]

Arguments

x
y       Specifies the x and y coordinates of the void (upper left corner).

w
h       Specifies the width and height of the rectangle

mode    Optional. Specifies the behavior of the mouse pointer, when the
        void is hit. Valid values are 'd', 'u', 'l', 'r' (short for: down,
        up,	left, right). The default is 'd', where the mouse pointer is
        always warped to the bottom of the void (+1), while the vertical
        coordinate remains unchanged.

Description

The XCreateMouseVoid function paints a black rectangle at the given coordinates. If the mouse pointer enters the rectangle, it is warped to a position outside the rectangle.

The code does not occupy CPU (polling approaches would), if the rectangle is not hit. The X server only notifies the program, when the mouse pointer enters the rectangle.

Author

Written by Patrick Stalph.

Reporting Bugs

Report bugs to patrick.stalph@gmx.de

Example

At work, I have my laptop with one additional screen plugged into the VGA of my laptop. The left monitor has a resolution of 1280*1024, while my laptop monitor has a resolution of 1280*800. Laptop is right-of the main monitor, bottom- aligned. It looks like this:

+----------------+ - - - - - - - -
|                |   THE VOID     '
|                +----------------+
|                |                |
|  VGA monitor   |     laptop     |
|                |                |
+----------------+----------------+

Consequently, the void starts at coordinates (1280, 0) and spans 1280*224 pixels. In default behavior, the mouse pointer will be blocked from entering this void from all direction. Thus, calling

XCreateMouseVoid 1280 0 1280 223

creates a rectangle that exactly covers the invisible area of the virtual screen. Furthermore, the mouse pointer is always blocked from entering that rectangle.

If an optional mode of 'd' is specified, the mouse will move downwards when hitting the left side of the void and the pointer will move to the right screen and continue along the bottom edge of the void. If the pointer hits the bottom of the void, it should just be blocked. In both cases the behavior is to warp the mouse pointer downwards. Thus, executing

XCreateMouseVoid 1280 0 1280 223 d

creates a rectangle that exactly covers the invisible area of the virtual screen. Furthermore, the mouse pointer is always warped to the bottom of the void, that is to the top edge of the visible area of the laptop screen.

Automating Execution

You can start XCreateMouseVoid from the X startup scripts (xinitrc). For example, on some distributions the following command (for instance) could be added to the user created file /etc/X11/xinit/xinitrc.d/dual-monitor.sh:

XCreateMouseVoid 1280 0 1280 223 &

To run this at the startup on Ubuntu, you could use:

System -> Preferences -> Startup Applications

Important: Take care, when using your computer with beamers or generally in varying environments. If blindly activated on startup every time, you may endup having a black rectangle on your next presentation :) In this emergency case, enter a terminal and type:

killall XCreateMouseVoid

Known Problems

Sometimes the mouse pointer is flickering when hitting the void, because the cursor changes its icon.

The code won't run without an X server. The connection is established using the DISPLAY environment variable.

Of course it doesn't make sense to run this code in environments without an X server.

Compiling the Code

Execute make in the XCreateMouseVoid source directory.

Steven--/XCreateMouseVoid