Say a list item's text when a swipe scrolls it into view

[aaron-gh]

When a swipe moves to a list item that is only partly on screen, the list scrolls it into view. But since #42, Backtalk works out what to say as soon as it sets focus, which is before the list has scrolled. The item's text was in children still past the edge of the list, and descriptions leave out off-screen children, so only the item's place in the list was said. For example, item 20 in Individual sounds and vibrations was just "20 of 80". The announcement prepared ahead for the next swipe (#43) had the same problem.

By default, such an item is now spoken from the app's focus event, which comes after the scroll, as in TalkBack, and nothing is prepared ahead for it. All other swipes still get the faster speech.

A new switch, Advanced settings > Reduce delay > Speak items before they scroll into view, speaks these items straight away instead. When Backtalk describes the item a swipe is moving to, children that are off screen only because of where they are count as on screen, since they will be once the list has scrolled. Android clamps each node's bounds on screen to every parent's, so a child wholly past the edge of the list comes out with inside-out bounds, its top below its bottom. A child that is hidden, or shrunk to nothing, keeps bounds the right way round, so it is still left out. An earlier version counted any empty bounds, which read a zero-size, unlabeled button in each notification in the shade as "Button".

Why it's off by default: an app that follows Android's conventions hides views it doesn't show, and lets its lists scroll a whole item into view. Such apps work correctly with this switch on. But not every app follows them, and the switch is off by default to protect users from those that don't. With it on, in such an app:

• a part that the app keeps out of sight by moving it outside its item, instead of hiding it, is read even though it isn't shown
• if the list can't scroll the whole item into view, the parts that stay off screen are read too

Neither changes where focus goes, only what is said.

Limitations: with the switch off, swipes that scroll an item into view are as slow as they were before #42.