A friend of mine who mainly works in Linux is always frustrated when he has to deal with working in Windows and doesn’t have FFM (Focus Follows Mouse). FFM means focusing a window when the mouse cursor moves over it (rollover), preferably without raising the window’s z-order position. I told him I’d throw together a program that did this, but my original approach was problematic.

My original approach was to use LowLevelMouseProc (WinAPI:SetWindowsHookEx), which is the same basic approach as my HalfKey project. Whenever a non-focused window (WinAPI:GetActiveWindow) is moused over (WinAPI:WindowFromPoint), it would activate it (gain the focus) (WinAPI:SetWindowLong/WinAPI:SetForegroundWindow). Unfortunately, as I found out, Windows is specifically designed to make an activated window go to the top of the z-order, and there is no way around this. The only solution I could find was recording the original position of the activated window (WinAPI:GetParent) and restoring it after the operation. This was however less than optimal :-(.

After some additional research on the topic, I found out the FFM functionality is actually built into Windows through a little known “System Parameter” (WinAPI:SystemParametersInfo). Microsoft calls it “Active Window Tracking”. Below is the code to the FocusFollowsMouse.exe (command line executable) to activate this system feature (the executable can be run without the command line and it will use the default options).

FocusFollowsMouse program information:
Turns on active window tracking in Windows
Parameters:

• -h The help screen (cancels further actions)
• -i installs new settings permanently
• -d disables active window tracking
• -r raise the window when focusing

//Toggles active window tracking, with options
#include <windows.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
	BOOL SendUpdate=SPIF_SENDCHANGE; //How to send the update to the system. Default is to only send to the system, but not make the change permanent
	BOOL TurnOn=TRUE; //By default we are turning on the option
	BOOL RaiseWindow=FALSE; //Whether to raise the window that is gaining the focus
	int i;

	//Read in options
	for(i=1;i<argc;i++)
	{
		if(argv[i][0]!='-') //Parameters must start with a -
			continue;
		switch(argv[i][1]) //Execute a valid action on the first character. Characters after it are ignored
		{
			case 'h': //Help  screen
				printf("%s", "Turns on active window tracking in Windows\n"
					"-h this help screen (cancels further actions)\n"
					"-i installs new settings permanently\n"
					"-d disables active window tracking\n"
					"-r raise the window when focusing\n");
					return 0; //Cancel further actions
			case 'i': //Install permanently
				SendUpdate|=SPIF_UPDATEINIFILE; //Writes the new system-wide parameter setting to the user profile.
				break;
			case 'd': //Turn off76
				TurnOn=FALSE;
				break;
			case 'r': //Raise the window
				RaiseWindow=TRUE;
				break;
		}
	}

	//Execute the system parameters change
	SystemParametersInfo(SPI_SETACTIVEWINDOWTRACKING, 0, (PVOID)TurnOn, SendUpdate);
	SystemParametersInfo(SPI_SETACTIVEWNDTRKZORDER, 0, (PVOID)RaiseWindow, SendUpdate);

	return 0;
}