Basically, modal windows had their own thread-locking for what
drawing was possible. This is a bit nonsense now we have a
game-thread. And it makes much more sense to do things like
NewGRFScan and GenerateWorld in the game-thread, and not in a
thread next to the game-thread.
This commit changes that: it removes the threads for NewGRFScan
and GenerateWorld, and just runs the code in the game-thread.
On regular intervals it allows the draw-thread to do a tick,
which gives a much smoother look and feel.
It does slow down NewGRFScan and GenerateWorld ever so slightly
as it spends more time on drawing. But the slowdown is not
measureable on my machines (with 700+ NewGRFs / 4kx4k map and
a Debug build).
Running without a game-thread means NewGRFScan and GenerateWorld
are now blocking.
This because video-drivers might need to make changes to their
context, which for most video-drivers has to be done in the same
thread as the window was created; main thread in our case.
This allows drawing to happen while the GameLoop is doing an
iteration too.
Sadly, not much drawing currently can be done while the GameLoop
is running, as for example PollEvent() or UpdateWindows() can
influence the game-state. As such, they first need to acquire a
lock on the game-state before they can be called.
Currently, the main advantage is the time spend in Paint(), which
for non-OpenGL drivers can be a few milliseconds. For OpenGL this
is more like 0.05 milliseconds; in these instances this change
doesn't add any benefits for now.
This is an alternative to the former "draw-thread", which moved
the drawing in a thread for some OSes. It has similar performance
gain as this does, although this implementation allows for more
finer control over what suffers when the GameLoop takes too
long: drawing or the next GameLoop. For now they both suffer
equally.
Drawing in a thread is a bit odd, and often leads to surprising
issues. For example, OpenGL would only allow it if you move the
full context to the thread. Which is not always easily done on
all OSes.
In general, the advise is to handle system events and drawing
from the main thread, and do everything else in other threads.
So, let's be more like other games.
Additionally, putting the drawing routine in a thread was only
done for a few targets.
Upcoming commit will move the GameLoop in a thread, which will
work for all targets.
The video drivers using the OpenGL backend are currently our only
accelerated drivers. The options defaults to off for macOS builds and
to on everywhere else.
Co-authored-by: Michael Lutz <michi@icosahedron.de>
The bootstrap has the _switch_mode to SM_MENU, and never leaves
this mode. Neither is it considered a modal window (while in some
sense it really is). So .. we need to add another "draw anyway"
exception, to make sure bootstrap is being drawn.
MainLoop() is used to bootstrap OSX, where later a callback is
done to GameLoop() to execute OpenTTD. All other video drivers
don't need that, so what is in GameLoop is in MainLoop for all
other drivers. This is rather confusing. So, instead, name
GameLoop MainLoopReal to be more in sync with the other drivers.
This makes it a bit easier to follow what is going on, and
allow future subdrivers to hook into a few of these functions.
Reworked the code slighly while at it, to return early where
possible.
