Base container control for popups and dialogs. Popup is a base [Control] used to show dialogs and popups. It's a subwindow and modal by default (see [Control]) and has helpers for custom popup behavior. Popup (show the control in modal form). Popup (show the control in modal form) in the center of the screen relative to its current canvas transform, at the current size, or at a size determined by "size". Popup (show the control in modal form) in the center of the screen relative to the current canvas transform, clamping the size to [code]size[/code], then ensuring the popup is no larger than the viewport size multiplied by [code]fallback_ratio[/code]. Popup (show the control in modal form) in the center of the screen relative to the current canvas transform, ensuring the size is never smaller than [code]minsize[/code]. Popup (show the control in modal form) in the center of the screen relative to the current canvas transform, scaled at a ratio of size of the screen. If [code]true[/code], the popup will not be hidden when a click event occurs outside of it, or when it receives the [code]ui_cancel[/code] action event. This signal is emitted when a popup is about to be shown. (often used in [PopupMenu] for clearing the list of options and creating a new one according to the current context). This signal is emitted when a popup is hidden. Notification sent right after the popup is shown. Notification sent right after the popup is hidden.