It is possible to overlap several objects in a Visual Adelia window.
In case of an overlap, the object placed on top has a transparent background so the object underneath is visible.
Transparency is only permitted for the following graphical objects:
Transparency is activated by the OVERLAP property when it is set to *TRUE value.
Note: For the image object, the image format must of course allow transparency to be managed.
In the window, it is necessary to set the FORCE_REDRAWN_OBJECTS property to the *TRUE value in order to avoid object refresh problems.
In the layout manager, the overlapped object is placed after the covered object, i.e. it is later in the window control order.
By default, an object is not drawn on an object which overlaps it and is before it in the order. The OVERLAP property set to *TRUE changes this behavior and authorizes the overlaid object to be drawn on top of the object placed before it.
Note: When managing events on program execution, it is the covered object that receives the user's actions whereas the overlaid object does not respond to any action. This means that the user receives the events from the covered object but not from the overlapped object (insofar as the two objects overlap). In order for the overlapped object to receive the user's actions, the covered object's ACTIVE property must be set to *FALSE.
If the developer overlaps objects on an image, the conventional case is a background image occupying the whole window area. He must set the image object's ACTIVE property to *FALSE to be able to select the objects on the layout and be able to access its properties.
Note: In the previous example, an "overlaid" object must be placed after the background image, whereas a "non-overlaid" object must be placed before the background image.
To properly manage the tab order of the objects in the window, the OVERLAP property is also defined for objects that do not support transparency. This concerns the following objects: