Simulating mouse input programmatically in OS X

Is it possible to simulate the actions of a mouse from a program in OS X? Specifically, the short version is that I'm trying to simulate a touchscreen using two webcams. So assuming I can get X,Y positions, can I send information to the OS as a mouse movement or click?

Edit- Or if it's particularly easy in another operating system I'd be willing to consider that.

Yes, it is possible. You can use the Quartz Event Services to simulate input events.

Assuming C, I wrote this quick example:

#include <ApplicationServices/ApplicationServices.h>
#include <unistd.h>

int main() {
	// Move to 200x200
	CGEventRef move1 = CGEventCreateMouseEvent(
		NULL, kCGEventMouseMoved,
		CGPointMake(200, 200),
		kCGMouseButtonLeft // ignored
	);
	// Move to 250x250
	CGEventRef move2 = CGEventCreateMouseEvent(
		NULL, kCGEventMouseMoved,
		CGPointMake(250, 250),
		kCGMouseButtonLeft // ignored
	);
	// Left button down at 250x250
	CGEventRef click1_down = CGEventCreateMouseEvent(
		NULL, kCGEventLeftMouseDown,
		CGPointMake(250, 250),
		kCGMouseButtonLeft
	);
	// Left button up at 250x250
	CGEventRef click1_up = CGEventCreateMouseEvent(
		NULL, kCGEventLeftMouseUp,
		CGPointMake(250, 250),
		kCGMouseButtonLeft
	);
	// Now, execute these events with an interval to make them noticeable
	CGEventPost(kCGHIDEventTap, move1);
	sleep(1);
	CGEventPost(kCGHIDEventTap, move2);
	sleep(1);
	CGEventPost(kCGHIDEventTap, click1_down);
	CGEventPost(kCGHIDEventTap, click1_up);
	// Release the events
	CFRelease(click1_up);
	CFRelease(click1_down);
	CFRelease(move2);
	CFRelease(move1);
		return 0;
}

And assuming GCC, compile with:

gcc -o program program.c -Wall -framework ApplicationServices

Enjoy the magic.

Swift mouse move and click example:

func mouseMoveAndClick(onPoint point: CGPoint) { 
    guard let moveEvent = CGEvent(mouseEventSource: nil, mouseType: .mouseMoved, mouseCursorPosition: point, mouseButton: .left) else {
        return
    }
    guard let downEvent = CGEvent(mouseEventSource: nil, mouseType: .leftMouseDown, mouseCursorPosition: point, mouseButton: .left) else {
        return
    }
    guard let upEvent = CGEvent(mouseEventSource: nil, mouseType: .leftMouseUp, mouseCursorPosition: point, mouseButton: .left) else {
        return
    }
    moveEvent.post(tap: CGEventTapLocation.cghidEventTap)
    downEvent.post(tap: CGEventTapLocation.cghidEventTap)
    upEvent.post(tap: CGEventTapLocation.cghidEventTap)
}

If you don't want to compile things and are looking for a shell-based tool, Cliclick may be the solution.

Here is a working C program based on jweyrick's answer:

// Compile instructions:
//
// gcc -o click click.c -Wall -framework ApplicationServices

#include <ApplicationServices/ApplicationServices.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
  int x = 0, y = 0, n = 1;
  float duration = 0.1;

  if (argc < 3) {
    printf("USAGE: click X Y [N] [DURATION]\n");
    exit(1);
  }

  x = atoi(argv[1]);
  y = atoi(argv[2]);

  if (argc >= 4) {
    n = atoi(argv[3]);
  }

  if (argc >= 5) {
    duration = atof(argv[4]);
  }

  CGEventRef click_down = CGEventCreateMouseEvent(
    NULL, kCGEventLeftMouseDown,
    CGPointMake(x, y),
    kCGMouseButtonLeft
  );

  CGEventRef click_up = CGEventCreateMouseEvent(
    NULL, kCGEventLeftMouseUp,
    CGPointMake(x, y),
    kCGMouseButtonLeft
  );

  // Now, execute these events with an interval to make them noticeable
  for (int i = 0; i < n; i++) {
    CGEventPost(kCGHIDEventTap, click_down);
    sleep(duration);
    CGEventPost(kCGHIDEventTap, click_up);
    sleep(duration);
  }

  // Release the events
  CFRelease(click_down);
  CFRelease(click_up);

  return 0;
}

Hosted at https://gist.github.com/Dorian/5ae010cd70f02adf2107