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Viewport and canvas transforms


This is an overview of the 2D transforms going on for nodes from the moment they draw their content locally to the time they are drawn onto the screen. This overview discusses very low level details of the engine.

The goal of this tutorial is to teach a way for feeding input events to the Input with a position in the correct coordinate system.

A more extensive description of all coordinate systems and 2d transforms is available in 2D coordinate systems and 2D transforms.

Canvas transform

As mentioned in the previous tutorial, Canvas layers, every CanvasItem node (remember that Node2D and Control based nodes use CanvasItem as their common root) will reside in a Canvas Layer. Every canvas layer has a transform (translation, rotation, scale, etc.) that can be accessed as a Transform2D.

Also covered in the previous tutorial, nodes are drawn by default in Layer 0, in the built-in canvas. To put nodes in a different layer, a CanvasLayer node can be used.

Global canvas transform

Viewports also have a Global Canvas transform (also a Transform2D). This is the master transform and affects all individual Canvas Layer transforms. Generally, this is primarily used in Godot's CanvasItem Editor.

Stretch transform

Finally, viewports have a Stretch Transform, which is used when resizing or stretching the screen. This transform is used internally (as described in Multiple resolutions), but can also be manually set on each viewport.

Input events are multiplied by this transform but lack the ones above. To convert InputEvent coordinates to local CanvasItem coordinates, the CanvasItem.make_input_local() function was added for convenience.

Window transform

The root viewport is a Window. In order to scale and position the Window's content as described in Multiple resolutions, each Window contains a window transform. It is for example responsible for the black bars at the Window's sides so that the Viewport is displayed with a fixed aspect ratio.

Transform order

To convert a CanvasItem local coordinate to an actual screen coordinate, the following chain of transforms must be applied:


Transform functions

The above graphic shows some available transform functions. All transforms are directed from right to left, this means multiplying a transform with a coordinate results in a coordinate system further to the left, multiplying the affine inverse of a transform results in a coordinate system further to the right:

# Called from a CanvasItem.
canvas_pos = get_global_transform() * local_pos
local_pos = get_global_transform().affine_inverse() * canvas_pos