Receiving, Filtering, and Modifying Mouse Events
The following is an example of programmatically receiving mouse events, with the option of filtering and modifying them, on Mac OS X 10.4 and up.
// altermouse.c
// http://osxbook.com
//
// Complile using the following command line:
// gcc -Wall -o altermouse altermouse.c -framework ApplicationServices
#include <ApplicationServices/ApplicationServices.h>
static CGRect screenBounds;
// This callback will be invoked every time the mouse moves.
//
CGEventRef
myCGEventCallback(CGEventTapProxy proxy, CGEventType type,
CGEventRef event, void *refcon)
{
// Do some sanity check.
if (type != kCGEventMouseMoved)
return event;
// The incoming mouse position.
CGPoint location = CGEventGetLocation(event);
// We can change aspects of the mouse event.
// For example, we can use CGEventSetLoction(event, newLocation).
// Here, we just print the location.
printf("(%f, %f)\n", location.x, location.y);
// We must return the event for it to be useful.
return event;
}
int
main(void)
{
CFMachPortRef eventTap;
CGEventMask eventMask;
CFRunLoopSourceRef runLoopSource;
// The screen size of the primary display.
screenBounds = CGDisplayBounds(CGMainDisplayID());
printf("The main screen is %dx%d\n", (int)screenBounds.size.width,
(int)screenBounds.size.height);
// Create an event tap. We are interested in mouse movements.
eventMask = (1 << kCGEventMouseMoved);
eventTap = CGEventTapCreate(
kCGSessionEventTap, kCGHeadInsertEventTap,
0, eventMask, myCGEventCallback, NULL);
if (!eventTap) {
fprintf(stderr, "failed to create event tap\n");
exit(1);
}
// Create a run loop source.
runLoopSource = CFMachPortCreateRunLoopSource(
kCFAllocatorDefault, eventTap, 0);
// Add to the current run loop.
CFRunLoopAddSource(CFRunLoopGetCurrent(), runLoopSource,
kCFRunLoopCommonModes);
// Enable the event tap.
CGEventTapEnable(eventTap, true);
// Set it all running.
CFRunLoopRun();
// In a real program, one would have arranged for cleaning up.
exit(0);
}