typedef control button; typedef void (*actionfn)(button b);
button newbutton(char *text, rect r, actionfn fn);
The newbutton function creates a push-button control, with the given text string being centered within the button. The button will appear on the last window which was created.
When the user clicks on the button with the mouse, the specified action function fn is called. The parameter to this action function will be the button which called the function.