ADD A CUSTOM PROGRESS BAR

[seel-channel]

I want to show a CustomProgressBar but the ModelViewer arguments don't have onPageStarted and onPageFinished. Please add the arguments :+1:

[KevinRohn]

Hi @seel-channel I created a pr with the requested requirement. There is a callback function final VoidCallback onModelIsVisisble; which is invoked when the model has loaded and is also visible, see: https://modelviewer.dev/docs/#entrydocs-loading-events-modelVisibility