A layer acts like a transparent sheet upon which shapes can be placed, sub-layers within layers to any desired depth are supported. Layers provide a mechanism for overlaying groups of views on top of each other. Layers can also clip their contents to exclude any content outside a user defined area.

Layers can be 2D or 3D, defined by their behaviour property.

When a layer is added to the stage, it is assigned a unique depth value. By default the stage has a root layer with a depth value of 0.

Layers are actors and inherit the position, orientation and scale of their parent actor. Layers are drawn in an order determined by a layer depth value.

Layers can be positioned anywhere in the actor tree. The layer draw order is always defined by the depth value.

// C++ example of adding a actor to the root layer

//  using stage.add() will automatically add actor to the root layer
Stage stage = Stage::GetCurrent();
stage.add( myActor );

// Or you can explicitly add an actor to the root layer.
Layer rootLayer = stage.GetRootLayer();
rootLayer.add( myActor );  // adds an actor to the root layer

Layer Specific Properties

• Layer::Property::CLIPPING_ENABLE
• Layer::Property::CLIPPING_BOX
• Layer::Property::BEHAVIOR : which can be Dali::Layer::LAYER_UI (default), or Dali::Layer::LAYER_3D

Layer clipping

Clips the contents of the layer to a rectangle.

Re-ordering layers

A range of functions are provided to change the draw order of the layers.

Rendering order of Actors inside of a layer

Layer_UI

Background

• Graphics are drawn in DALi using renderers
• Actors can have zero or many renderers
• Renderers can be shared by actors
• Renderers have a depth index property

With Dali::Layer::LAYER_UI, the draw order of the renderers is defined by both:

• Renderer depth index.
• Position of actor in the actor tree

Layer_3D

Set Layer behavior to Dali::Layer::LAYER_3D;

Opaque renderers are drawn first and written to the depth buffer.

Transparent renderers are drawn in order of distance from the camera ( painter’s algorithm ).

Actor drawing mode

• DrawMode::OVERLAY_2D

Inside a layer, it is possible to force tree views to be drawn on top of everything else in the layer.