There is an Xposed module called Gravitybox(http://repo.xposed.info/module/com.c...kat.gravitybox
) . It somehow works on my Galaxy S4 on TouchWiz, but it is designed to work with AOSP based ROMs like cyanogenmod. When you install that module and install the Xposed Framework, you'll get a new entry in your list of shortcuts as you can see in the screenshot I attached. That shortcut allows you to do a lot of useful actions, INCLUDING TAKING A SCREENSHOT. To access the shortcut, you'll need another app to work over any app that you're currently using. That app is called GMD GestureControl (https://play.google.com/store/apps/d...gesturecontrol
). Install that app, and then set a gesture to take a screenshot using the shortcut provided by Gravitybox module.
Another option is just to use Gravitybox and use the screenshot action to trigger when you, for example, long-press the clock at the top of your notification panel or when you long-press the back button, these are all options that can be customized in the Gravitybox module.
Keep in mind that you need to be rooted, not use the ART runtime, and have Xposed Framework installed on your device. I hope this helps.