Use logarithmic scaling for zoom mode

Author: myQwil

src/events.c

@@ -543,14 +543,8 @@ static void feh_event_handle_MotionNotify(XEvent * ev)
 
 		winwid = winwidget_get_from_window(ev->xmotion.window);
 		if (winwid) {
-			if (ev->xmotion.x > winwid->click_offset_x)
-				winwid->zoom = winwid->old_zoom + (
-						((double) ev->xmotion.x - (double) winwid->click_offset_x)
-						/ 128.0);
-			else
-				winwid->zoom = winwid->old_zoom - (
-						((double) winwid->click_offset_x - (double) ev->xmotion.x)
-						/ 128.0);
+			winwid->zoom = winwid->old_zoom *
+				exp((double)(ev->xmotion.x - winwid->click_offset_x) / 128.0);
 
 			if (winwid->zoom < ZOOM_MIN)
 				winwid->zoom = ZOOM_MIN;