1. On using the mouse
A brief introduction to LIBGPM: the General Purpose Mouse
programming interface

2. The Linux “gpm” package
It’s a mouse server for the Linux console
It “hides” details about mouse hardware
Intended for use with text-based programs
But we can use it with graphics programs
Requires that the gpm daemon is running
Type ‘info gpm’ to see official information
Also an online article by Pradeep Padala

3. Programming steps
Your client application must establish a connection with the gpm server-daemon
You need a header-file: #include <gpm.h>
You declare an important data-structure: Gpm_Connect conn;
You will need to initialize its four fields
Then you call Gpm_Open( &conn, 0 );
Returns -1 if unsuccessful (otherwise 0)

4. Fields to be initialized
conn.eventMask = ~0; // events of interest
conn.defaultMask = 0; // to handle for you
conn.minMod = 0; // lowest modifier
conn.maxMod = ~0; // highest modifer

5. Responding to mouse activity
You create your own ‘handler’ function for those mouse events that you wish to act upon
Prototype of the handler-function is: int my_handler( Gpm_Event *evt, void *my_data );
To install the handler, use this assignment: gpm_handler = my_handler;
Whenever the mouse is moved, or its buttons are pressed or released, your function executes

6. Useful fields in Gpm_Event
Gpm_Event *evt;
evt->type == 1: // indicates a mouse-move
evt->x, evt->y: // current mouse ‘hot-spot’
evt->dx, evt->dy: // changes in position(+/-)
NOTE: Remember that GPM was developed for text-based applications, so the hot-spot coordinates are character-cell locations (not graphics-pixel locations)

7. A typical program loop
This loop allows normal keyboard input to continue being processed (e.g., echoed, buffered) while any mouse activities are processed by your handler (or else by a default handler supplied by the daemon)
int c;
While ( ( c = Gpm_Getc( stdin ) ) != EOF );
Gpm_Close();

8. A simple text-mode demo
Pradeep Padala has published a short C program that illustrates ‘barebones’ usage of the gpm package (from Linux Journal)
We have adapted his code for C++
Our demo is called ‘trymouse.cpp’
It’s compiled like this:
$ g++ trymouse.cpp –lgpm –o trymouse

9. A simple graphics demo We have created a minimal graphics demo
It shows how you could use the mouse to move a ‘slider’ object (e.g.,in Pong game)
It’s called ‘gpmslide.cpp’
You compile it like this: $ g++ gpmslide.cpp –lgpm –o gpmslide

10. In-class exercises Compile and run the ‘trymouse.cpp’ demo
Compile and run the ‘gpmslide.cpp’ demo
Look at the C++ source-code in the demos
Can you replace the keyboard-based user controls (in your earlier pong animation) with mouse-based user-controls?
Can you incorporate mouse-based control into your 3D wire-frame model animation?