On using the mouseDiversity of hardwareExample: the PS/2 MouseThe Linux “gpm” packageProgramming stepsFields to be initializedResponding to mouse activityUseful fields in Gpm_EventThe GPM mouse-event maskA typical program loopA simple text-mode demoA simple graphics demoMore elaborate graphics demoOur mouse cursorOur mouse cacheIn-class exercise #1Demo: ‘persists.cpp’In-class exercise #2On using the mouseA brief introduction to LIBGPM: the General Purpose Mouse programming interfaceDiversity of hardware•As with SVGA devices, there are computer mice from a diversity of vendors – and no universal standard hardware design•The customary solution: a software layer is created which ‘hides’ hardware differences•For Linux platforms, the ‘libgpm’ package provides one such software-layer – though it was intended for text-based applicationsExample: the PS/2 MouseX-coordinate data (bits 7..0)Y-coordinate data (bits 7..0)Byte 0Byte 1Byte 2The Mouse Report Format (3 bytes)LeftButtondownRightButtondownMiddleButtondown0X-datasignY-datasignY-dataoverflowX-dataoverflow7 6 5 4 3 2 1 0Other types of computer mice use different report formats with possibly a different number of bytes (e.g., 4 or 5)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 PadalaProgramming 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 initializedconn.eventMask = ~0; // events of interestconn.defaultMask = 0; // to handle for youconn.minMod = 0; // lowest modifierconn.maxMod = ~0; // highest modiferResponding 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 executesUseful fields in Gpm_EventGpm_Event *evt;evt->type == 1: // indicates a mouse-moveevt->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)The GPM mouse-event maskLEAVEENTERHARDMOVCLKTRIPLEDOUBLESINGLEUPDOWNDRAGMOVE#include <gpm.h>Your event-handler function will ‘test’ one or more of these flag-bits to determine what type of state-change the mouse has undergone, so that your application can respond to it in an appropriate mannerA typical program loopThis 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 trymouseA 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 gpmslideMore elaborate graphics demo•We also created a more elaborate mouse-demo (called ‘seemouse.cpp’)•It defines its own custom mouse-cursor •It handles the four most common types of mouse events: –GPM_MOVE –GPM_DOWN–GPM_DRAG–GPM_UPOur mouse cursor•We built a 2-color 16-by-16 pixel image‘0’ = transparent color‘1’ = background color‘2’ = foreground colorWe used an array of character-stringsto define our image with only three character-valuesOur mouse cache•Each time we want to draw our cursor, we first copy the existing 16-by-16 pixel-grid that occupies the planned cursor-location•Then we can draw our cursor threre•When the mouse is moved, we need to ‘erase’ our cursor-image (by copying the saved background there), and then save-and-draw our cursor in the new locationIn-class exercise #1•Can you create a different cursor-image, based on your own design ideas? Will your design define a different ‘hot-spot’? Will you need to modify the boundaries to keep your cursor from going out-of-view?Demo: ‘persists.cpp’•We created a sound-playing program that plays a continuous tone – until a ‘signal’ is received (asynchronous notification) that the user has pressed the <ESCAPE> key•We used an ‘ioctl’ command to ‘RESET’ the playback device – to stop the tone’s sound almost immediately when our user presses the <ESCAPE> keyIn-class exercise #2•Try commenting out the final ‘ioctl’() call in our ‘persists.cpp’ demo, then recompile it and execute that demo again. Does the sound cease immediately?•Can you incorporate the sound-effect into our ‘seemouse.cpp’ demo, so that a user can start the tone by pressing the mouse-button, and stop the tone by releasing
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