In the past it's been a recommended approach to avoiding overdraw for
apps to set their window background to null at runtime if their
content view fully covers their window surface. The problem with this
is the IME.
The IME can force a resize of the window at unexpected times and
unless an app has been configured to fit system windows and manually
cover the padded area that the IME window covers, the asynchronous
nature of the IME-show process can leave surface buffer garbage
visible to the user. In previous platform versions this wasn't an
issue since pre-renderthread we would always animate a crossfade from
the closed to open state. This animation was always a bit of a hack
since it could break the contract of requestLayout/invalidate on the
view hierarchy - it could result in a draw happening into the saved
"before" state of the crossfade before a pending layout.
Now that this has been cleaned up the buffer garbage is sometimes
visible.
To prevent this, PhoneWindow now detects the state of a null window
background and draws solid rects into the area not covered by a
window's content. Which color is determined by the window context's
theme, though this is not a public API available to apps.
Bug 17006497
Change-Id: I714439a1608c4ae135f3d9d49bb165330d9fbe9f
f849a5e16d