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Edit 2d/canvas_layers.rst

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Nathan Lovato
2020-11-04 12:57:45 -06:00
parent 356079cb38
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tutorials/2d/canvas_layers.rst
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@@ -6,31 +6,30 @@ Canvas layers
Viewport and Canvas items
-------------------------
Regular 2D nodes, such as :ref:`Node2D <class_Node2D>` or
:ref:`Control <class_Control>` both inherit from
:ref:`CanvasItem <class_CanvasItem>`, which is the base for all 2D
nodes. CanvasItems can be arranged in trees. Each item will inherit
its parent's transform. This means that when the parent is moved, the children
will move too.
:ref:`CanvasItem <class_CanvasItem>` is the base for all 2D nodes, be it regular
2D nodes, such as :ref:`Node2D <class_Node2D>`, or `Control
<class_Control>`. Both inherit from :ref:`CanvasItem <class_CanvasItem>`.
You can arrange canvas items in trees. Each item will inherit its parent's
transform: when the parent moves, its children move too.
CanvasItem nodes, and nodes inheriting from them, are direct or indirect children of a
:ref:`Viewport <class_Viewport>`, and will be displayed through it.
:ref:`Viewport <class_Viewport>`, that display them.
A Viewport has the property
:ref:`Viewport.canvas_transform <class_Viewport_property_canvas_transform>`,
which allows applying a custom
:ref:`Transform2D <class_Transform2D>` transform to the CanvasItem hierarchy it contains. Nodes such as
allows to apply a custom :ref:`Transform2D <class_Transform2D>`
transform to the CanvasItem hierarchy it contains. Nodes such as
:ref:`Camera2D <class_Camera2D>` work by changing that transform.
Effects like scrolling are best achieved by manipulating the canvas transform property. This approach is more
efficient than moving the root canvas item (and hence the whole scene).
To achieve effects like scrolling, manipulating the canvas transform property is
more efficient than moving the root canvas item and the entire scene with it.
Usually though, we don't want *everything* in the game or app to be subject to the canvas
transform. For example:
- **Parallax Backgrounds**: Backgrounds that move slower than the rest
of the stage.
- **UI**: Think of a user interface (UI) or head-up display (HUD) superimposed on our view of the game world. We want a life counter, score display and other elements to retain their screen positions even when our view of the game world changes.
- **UI**: Think of a user interface (UI) or Heads-up display (HUD) superimposed on our view of the game world. We want a life counter, score display and other elements to retain their screen positions even when our view of the game world changes.
- **Transitions**: We may want visual effects used for transitions (fades, blends) to remain at a fixed screen location.
How can these problems be solved in a single scene tree?