Allow Symbian widget implementations to select native paint mode

On the Symbian platform, the Qt raster paint engine targets an
off-screen buffer owned by the Font & Bitmap server (FBSERV).
When an area of the screen needs to be refreshed, the window
server (WSERV) asks the control environment (CONE) to redraw the
control(s) intersecting that screen region.  Each Qt native
widget has an associated Symbian control, whose Draw function
blits the required region of the backing store via WSERV.

Use cases involving Direct Screen Access (DSA) may require this
behaviour to be modified, to either of the following:

    - Disable: the Draw function does nothing.  In this case,
    the output of paint events, rendered to the backing store,
    is not blitted to the screen.  This mode was introduced by
    change 8f445e13.

    - Zero fill: the Draw function fills all pixels within the
    redraw region with zeroes.

This change allows the widget implementation to select either of
these alternative modes by setting a flag in its QWExtra structure.

Note that these alternative modes are only suitable for native
widgets, because they act on a per-control rather than per-widget
basis.

Task-number: QTBUG-5467
Reviewed-by: Jason Barron

0 files changed, 0 insertions, 0 deletions