investigate: strategies for adjusting to environments getting sub-60 fps

Rather than doing artificial timing like with timers, the game uses framerate (via requestAnimationFrame(..)) for all its timings, with the assumed target of 60fps. Luckily, most good devices seem to be running the game very near that already. But old devices or those without defaulted hardware acceleration (like linux desktops!) are running at or below 45fps routinely, which makes current game play on those devices quite painful.

Note: Obviously, optimizing the game's code more is a good strategy all around. However, this thread assumes all that has already been tackled, and that there may still be environments where the best version of the code still runs slower than desired. In those cases, the game should have some strategy for adjusting itself.

Should the game track its own FPS (beyond dev/debugging, but obviously just not displayed)? Should it adjust itself if it determines that a device is running substantially under (or over?) the target 60fps? Should the game refuse to run if the effective fps is just too far below some reasonable threshold (like 20fps)?

The game could monitor fps and round to nearest 15fps increments (15, 30, 45, 60, etc), and then scale its timings accordingly. Or, if the fps is at or below 45, could scale down to 30 fps artificially, and just drop (aka, not draw) every other frame of its normal timings.

Or, it could detect a fps below some threshold like 50 and suggest the user pick a simple-graphics mode which maybe uses lower quality graphics.

Investigate all these possible strategies (and look for others?) and test them out on old devices (like iphone4 for example).