Previously, IDXGISwapChain::Present was called on a background thread,
which made it difficult to avoid race conditions. e.g. during a
live-resize of a window, we would occasionally draw old incomplete
frames instead of new frames at the correct size.
The new approach moves the Present call to the main thread via
AsyncUpdater. We attempt to present whenever the swap event wakes, and
whenever a frame is drawn. Only a single Present call may be made after
the swap event wakes. Subsequent Present calls will be ignored until the
next time the swap event wakes.
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.
