We shouldn't need more than 2 drawables, but changing the count from the
default of 3 introduces framerate lags in fullscreen mode.
This changes leaves the drawable count alone. No good deed goes
unpunished.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
The OpenGL (ES) implementations on Apple platforms are deprecated and
don't support GPU compute programs. This change adds support for the
replacement, the Metal GPU API.
Signed-off-by: Elias Naur <mail@eliasnaur.com>