Camera: Fix GI camera provider crash when no texture is available after loading

[Cheaterman]

Traceback:

   File "/home/cheaterman/Dev/Kivy/kivy/core/camera/camera_gi.py", line 137, in _update
     self.dispatch('on_load')
   File "kivy/_event.pyx", line 705, in kivy._event.EventDispatcher.dispatch
   File "kivy/_event.pyx", line 1248, in kivy._event.EventObservers.dispatch
   File "kivy/_event.pyx", line 1172, in kivy._event.EventObservers._dispatch
   File "/home/cheaterman/Dev/Kivy/kivy/uix/camera.py", line 112, in _camera_loaded
     self.texture_size = list(self.texture.size)
 AttributeError: 'NoneType' object has no attribute 'size'

Also see #6971.

[Cheaterman]

Might seem a bit aggressive but since we can't assume the texture is assigned in on_load... Regarding texture size, I'm not sure how guaranteed we are it won't change dynamically (say when your phone flips from portrait to landscape?), so that might be a better idea either way ; but for self.texture, if we can assume the same texture will be reused across the CoreCamera lifetime (even through start()s and stop()s), we could make sure to only assign it once?

I'm not sure that's a safe assumption either, so here we are.

[Cheaterman]

(FWIW I'm not quite sure how the Camera widget was invoked - I am using garden.zbarcam (which uses garden.xcamera) with default settings)

[wolfmanjm]

This indeed fixes the issue for me. My camera works again with master.

[Cheaterman]

Happy to help 😊

[pythonic64]

You don't have to convert to list because texture_size is a ListProperty and assigning to it will convert texture.size to ObservableList.

[pythonic64]

Actually, you don't have to set texture_size at all as it will be updated by on_texture method from Image class.

[pythonic64]

You can safely remove line self.texture_size = list(texture.size) from on_tex and _camera_loaded methods.

[akshayaurora]

We can still check and update only when texture is None or when camera.texture.size is not equal to self.texture_size, right ?

[matham]

Seems to have been fixed in #7071.

[Cheaterman]

TFW ^^" anyway at least it's fixed. The line deletions I've made might still be a good idea though - mo' code mo' problems.

[wolfmanjm]

FYI #7071 breaks gi based camera in 2.0.0, whereas this PR stops it crashing and allows it to work again.
I would recommend reverting #7071 and using this PR instead.

[matham]

This seems correct as a texture may not exist at on_load.

It would be nice to only update if the texture object changed, but this is definitely working it shouldn't cause much performance loss.

[Cheaterman]

And there you go 😊 thanks everyone !