[Development] More flexible window orientation API

[Samuel Rødal]

Hi,

we're working toward having a flexible yet simple API for window 
orientations. It's important that the QWindow orientation API is 
flexible enough to handle all use cases, whereas the APIs on top (in Qt 
components for instance) can offer some more convenience for application 
developers.

We've found that the current QWindow::setOrientation() API isn't 
sufficient to express all the different ways of doing orientation. 
Namely, it currently only allows you to tell the windowing system / 
compositor about how the contents of the window are rendered, and not 
how the window buffer itself should be interpreted. It's not always 
desirable to explicitly rotate the contents of the window, sometimes 
it's practical to be able to use a different buffer layout instead. As 
an example, a game being ported to a portrait device might still want to 
use a landscape buffer layout, if the game engine design makes it hard 
to rotate the rendered output to fit a portrait buffer layout. For a 
raster based game there are performance costs due to having to do a 
90-degree rotation.

So we should support both approaches, having a way to hint to the 
compositor both the window orientation and the content orientation.

My current patch, which replaces QWindow::setOrientation() with 
QWindow::setContentOrientationHint() and 
QWindow::setWindowOrientationHint() is already on Gerrit:

http://codereview.qt-project.org/#change,13397

Feedback is appreciated.

--
Samuel