The Renderer class supports z-axis layering by drawing and keeping widgets on top of others as shown in the figure beneath. Layers are set up automatically, whenever a widget with a certain depth does not match the existing layers. Thus you usually will not have to deal with the layer internals of the Renderer class, but instead adjust the layers using the different widgets. Sometimes it might be necessary to manually adjust portions of the layer behaviour, especially if layers should be activated automatically on certain actions.

Figure 4. Layer view on the display.

The currently active layer, which has the input focus, can be get and set using the active_layer attribute or set_active_layer() method.

layer = renderer.active_layer
renderer.set_active_layer (2)
        

You should not modify the contents nor the objects directly but instead use the respective Renderer methods instead.

The set_active_layer() methods accepts both, a tuple as returned by active_layer as well as an integer, which denotes the layer to activate (similarily to the depth attribute of the BaseWidget class).

Both, the method and attribute, allow you to manipulate the active layer directly, so that you can enforce the focus on a certain dialog window for example.

It is also possible to cycle through the layers programmatically,using the switch_layer() method. The figure beaneath shows, what happens on each invocation.

renderer.switch_layer () # Step 1
renderer.switch_layer () # Step 2
renderer.switch_layer () # Step 3
        

Figure 5. Layer cycling

To enhance the accessibility of widgets on the screen, the Renderer implements the IIndexable interface class to let the user navigate through widgets using the keyboard. Each installed layer manages its own indexing list, so that the navigation by default always happens on the currently active layer.

The Renderer determines the order, widgets are navigated through, using their index attribute. The invocation of switch_index() will set the keyboard focus to the widget with the next higher index value. If the last widget is reached, the first widget will receive the focus again as shown in the figure below.

Figure 6. Index switching