update readme

Author: marsqing

README.md

@@ -1,6 +1,64 @@
-OSX users will miss the three-finger-drag feature when switch to Linux. With that feature, you can easily select text or drag something around. On Linux, there are two options to achieve this:
-* [mtrack](https://github.com/p2rkw/xf86-input-mtrack)
-* [libinput-gestures](https://github.com/bulletmark/libinput-gestures)
+# THREE FINGER DRAG
+OSX users will miss the three-finger-drag feature when switch to Linux. With that feature, you can easily select text or drag something around. On Linux, there are two common options to achieve this:
+1. [mtrack](https://github.com/p2rkw/xf86-input-mtrack)
 
-[three-finger-drag issue](https://github.com/bulletmark/libinput-gestures/issues/10)
-[three-finger-drag fork](https://github.com/daveriedstra/libinput-gestures/tree/three-finger-drag)
+set the following options in xorg.conf and you get three-finger-track
+```
+Option "SwipeUpButton" "1"
+Option "SwipeDownButton" "1"
+Option "SwipeLeftButton" "1"
+Option "SwipeRightButton" "1"
+```
+
+The problems of mtrack are:    
+* not actively maintained
+* less "smooth" than libinput
+* not the default driver for trackpad of Manjaro or Ubuntu, and have some compatibility issues with GDM on my machine
+
+
+2. [libinput-gestures](https://github.com/bulletmark/libinput-gestures)
+
+libinput-gestures do not natively support three-finger-track. You need to use this fork [three-finger-drag fork](https://github.com/daveriedstra/libinput-gestures/tree/three-finger-drag) which is mentioned in this [libinput-gestures three-finger-drag issue](https://github.com/bulletmark/libinput-gestures/issues/10#issuecomment-441459797). As the author of libput-gestures [replied](https://github.com/bulletmark/libinput-gestures/issues/10#issuecomment-247980222), libinput-gestures won't support three-finger-track due to "To implement this would be messy, require significant processing overhead, and is discordant with the current design.". 
+
+so if you use the [three-finger-drag fork](https://github.com/daveriedstra/libinput-gestures/tree/three-finger-drag) of libinput-gestures:
+* you can't use new features of libinput-gestures because the two repos can not be merged easily
+* extra configuration is needed
+    ```
+    gesture swipebegin all 3 xdotool mousedown 1
+    gesture swipeend all 3 xdotool mouseup 1
+    gesture swipeupdate all 3 xdotool mousemove_relative -- x y
+    ```
+
+# INSTALLATION
+
+So with this tool, you can use three-finger-drag with libinput(the underlying tool libinput-gestures based on). You probably will use it with libinput-gestures side by side to add three-finger-drag support.
+```
+1. clone the repo
+2. install libinput(you probably have it already)
+3. install xdotool(which includes libxdo)
+4. cargo build --release
+5. copy target/release/libinput-three-finger-drag to somewhere
+6. disable 3 finger swipe gesture in libinput-gestures, see below
+6. run libinput-three-finger-drag and check whether it works
+7. make libinput-three-finger-drag auto-start
+```
+
+## Disable 3 finger swipe gesture in libinput-gestures
+Modify libinput-gestures config file /etc/libinput-gestures.conf or ~/.config/libinput-gestures.conf. 
+Add finger_count 4 to essentially disable 3 finger swipe.
+
+change
+``` 
+gesture swipe up  xdotool key super+Page_Down 
+```
+to
+```
+gesture swipe up  4  xdotool key super+Page_Down
+```
+
+# HOW IT WORKS
+Just like libinput-gestures. Fork
+```
+libinput debug-events
+```
+and read the output, which is trackpad "raw events". Filter out events of GESTURE_SWIPE_BEGIN, GESTURE_SWIPE_UPDATE and GESTURE_SWIPE_END. Simulate mouse_down on BEGIN, mouse_relative_move on UPDATE and mouse_up on END with libxdo. These three mouse action simulate a three-finger-drag. Call libxdo is more efficient than fork xdotool like libinput-gestures does. Especially when processing GESTURE_SWIPE_UPDATE events which is more frequent than BEGIN and END.