The FPS counter was based on metrics in the nvdisp swapbuffers call. This metric would be accurate if the gpu thread/renderer were synchronous with the nvdisp service, but that's no longer the case.
This commit moves the frame counting responsibility onto the concrete renderers after their frame draw calls. Resulting in more meaningful metrics.
The displayed FPS is now made up of the average framerate between the previous and most recent update, in order to avoid distracting FPS counter updates when framerate is oscillating between close values.
The status bar update frequency was also changed from 2 seconds to 500ms.
The general pattern is to mark mutexes as mutable when it comes to
matters of constness, given the mutex acts as a transient member of a
data structure.
The follow-up to e2457418da, which
replaces most of the includes in the core header with forward declarations.
This makes it so that if any of the headers the core header was
previously including change, then no one will need to rebuild the bulk
of the core, due to core.h being quite a prevalent inclusion.
This should make turnaround for changes much faster for developers.
Now based on std::chrono, and also works in terms of emulated time
instead of frames, so we can in the future frame-limit even when the
display is disabled, etc.
The frame limiter can also be enabled along with v-sync now, which
should be useful for those with displays running at more than 60 Hz.
