What's the closest widget to implement this after-effects feature in Gtk

wisgetwas wondering what widget in gtk (using gtkmm) could be used to implemented the movable button looking thing in the picture. and also the dotted line. dotted line edit: the widget is supposed to be able to move left and right along the time-track to be able to set the play bounds. Here is a video showing how it looks like in after effects. From sescond 37 is how the behaviour for it supposed to be. https://www.youtube.com/watch?v=QxXevteeumg

edit: from what it looks like there isnt a specific widget which could simplify this. However a regular button can be used and then implementing a method for its drage using the various signal handlers associated with a Gtk button

There is no widget that does this (see the widget gallery).

You can, however, add custom widgets using Cairo. In the official Gtkmm book, there is an example for creating a custom clock widget using the Gtk::DrawingArea. The Gtk::DrawingArea offers a lot of signals which you can connect to.

I have created my own widgets in the past using this and it worked just fine. However, it was a lot of work because:

1. Cairo lacks good documentation. Understanding the philosophy behind this library is a lot of work, often empirical.
2. It can be hard to acheive acceptable performance using Cairo. One has to be really careful in how the drawing of the widget is performed. There is often a naive way to do it, which is clearer in the code, but devastating in terms of performance (it often involves useless redraws on the CPU).