Optionalautotrue — mount it when work starts
and it shows itself; unmount it when the work ends.
Pass false to keep the panel mounted but idle and drive it with showLoadingPanel /
hideLoadingPanel. Both modes obey the same rule — the fade must be COMMITTED before the
caller blocks the main thread — but a panel mounted at the moment work begins has never been
painted, so committing it costs a mount, a first paint of a full-screen layer, and the wait for
transitionrun below. An already-mounted panel is already painted: one frame and it is armed.
OptionaliconOptionallabelOptionalonOptional callback when mounted
OptionalonOptional callback when unmounted
OptionalpanelWrap the icon and label in a paper panel.
OptionalprogressDeterminate progress as a fraction in [0, 1]. When a number, a determinate progress bar and
percentage are shown in place of the animated icon; when null/undefined the indeterminate
icon is shown.
OptionalrefRef to the element.
OptionaltransitionA delay for showing the loading panel.
OptionaltransparentWhether the background should be transparent.
Begin the fade-in as soon as the panel mounts.