Transcript On using the mouse A brief introduction to LIBGPM: programming interface

On using the mouse
A brief introduction to LIBGPM:
the General Purpose Mouse
programming interface
The Linux “gpm” package
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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
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)
Fields to be initialized
conn.eventMask = ~0;
conn.defaultMask = 0;
conn.minMod = 0;
conn.maxMod = ~0;
// events of interest
// to handle for you
// lowest modifier
// highest modifer
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
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)
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();
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
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
In-class exercises
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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?