Function returns state instead of value

Question

I want to make a mesh preview. I created a function that returns a texture for a button with TextureRect, but it returns a gdscript function state.

func render_thumbnail(_mesh, size, screen):
    var new_viewport = viewport.instance()
    new_viewport.size = screen
    add_child(new_viewport)
    var camera = new_viewport.find_node("Camera")
    camera.size = size
    if _mesh:
        var mesh = new_viewport.find_node("Mesh")
        mesh.set_mesh(_mesh)

    var thumbnail = ImageTexture.new()
    for a in 2: yield(get_tree(), "idle_frame")
    var image = new_viewport.get_texture().get_data()
    thumbnail.create_from_image(image)
    new_viewport.queue_free()
    return thumbnail

It seems to me that this is due to yield (), but I do not know how to fix this or how to replace it...

Answer 1

Yes this is because of yield.

I think the simplest way is to declare a signal for when the thumbnail render has finished and use that instead of return
All in one class:

signal thumbnail_finished(thumbnail)

func _ready():
    self.connect("thumbnail_finished", self, "_process_rendered_thumbnail")

func _render_thumbnail(_mesh, size, screen):
    # all the code in the render_thumbnail function except for the last line
    emit_signal("thumbnail_finished", thumbnail) # instead of return thumbnail

func _process_rendered_thumbnail(thumbnail):
    # This function gets called when the thumbnail has finished rendering
    # Do stuff
    pass

Answer 2

You can still keep the yield!

If you don't want to change a code that you wrote just to get the right return value, or you just don't want to use extra signals you can just use another yield when calling the function!

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So in your case you can say;

var thumbnail = yield(render_thumbnail(mesh, size, screen), "completed")

important part is "completed" it will only set thumbnail to render_thumbnail when it returns an actual value!