I think you misunderstood the widget I'm describing. It is swipeable meaning I swipe to pull the sidebar into view and swipe to push it out of view. If I stop half way the sidebar stops where my finger stops.
Meaning the sidebar has to follow my finger, at 60fps, as I quickly swipe in and out. If such a thing is as easy you claim then a quick demo should be easy enough. I know of no such sidebars on the web that fit this requirement, but am happy to hear all of those devs (and myself!) are just terrible at their (my) jobs.