Partially reverts a change made in
362a1cc070.
The factory needs to be multithreading-enabled in order to support e.g.
drawing to the screen on the main thread and drawing to an Image on a
background thread, even when no resources other than the graphics device
are shared between the two threads.
Reverts b12088a1f6
After some investigation, it appears that ClearType rendering is
unsuitable when
- the render target has translucent pixels underneath rendered text, or
- the render ouput is rotated, scaled, subpixel-translated, or otherwise
transformed before display.
This necessitates avoiding ClearType when rendering into transparent
bitmaps.
Unfortunately, a commmon use-case for transparent bitmaps is buffered
component images. Even if ClearType were enabled for opaque targets,
ClearType text could then end up displaying next to non-ClearType text
rendered to an intermediate texture, leading to an inconsistent
appearance.
There's also not a straightforward way of exposing a ClearType rendering
option in all of the places that it would be required, and a change of
this size is difficult to justify given that subpixel text rendering
controls would only have an effect on Windows.
