I have a complex drawing on a Gtk DrawingArea widget and I wish to provide the user with a way to select a rectangle on it to expand for a closer view. I have managed to get the necessary mouse button events sorted out so that the rectangle can be selected, but it would be desirable to have the actual rectangle drawn on the display, moving around along with the mouse. I need to know how one does this without disturbing the underlying drawing (i.e. so I can erase the temporary rectangle as it changes size and shape without having to redraw the underlying picture).
Could someone tell me the correct name for this effect (so that I can google it) or does anyone know of an example, or a keyword to search the Gtk documentation?
Thank you.
You are looking for the Rubber Band technique.