I want to have MyTexture.tres to generate the Image, and be able to visualise it both at run time and in the editor.

The goal is to have my own Texture type as a Resource file, that can be used like NoiseTexture, GradientTexture, etc, and to use it in the editor (on a Sprite, as a shader uniform...) and NOT to save any image data in project folder.

tool
extends ImageTexture

export var width := 100
export var height := 100


func _init():
    var image := Image.new()
    
    # ...
    # Generate the image data array
    # ...

    create_from_image(image)

Using the tool keyword, it works but the Image data is automatically saved into MyTexture.tres, so it break the best advantage that is to save a lot of space.

I assign a script to the .tres file trying inheriting both ImageTexture and ProxyTexture, but the result is the same once I call create_from_image() it saves it to the file.

[sub_resource type="Image" id=3]
data = {
"data": PoolByteArray( 127, 119, 254, 131, 131, 119, 25, ... ) <-----
"format": "RGBA8",
"height": 512,
"mipmaps": false,
"width": 512
}

May be I will try inheriting ViewportTexture but even if it works it seem wrong, that require accessing the SceneTree to instanciate the Viewport (from a Resource script), may be is there a clean way ?