Avoid "spiral of death" by capping maximum number of ticks per frame #42
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Bug
The observed behaviour is incorrect or unexpected.
C-Low Hanging Fruit
Ideal issue for new contributors.
S-Moderate
The fix or feature would substantially improve user experience.
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byorgey
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This is in order to avoid the "spiral of death", see https://gafferongames.com/post/fix_your_timestep/. Set the maximum number of ticks in a single game (arbitrarily) to 30. To observe this in effect, try going into creative mode, cranking up the ticks per second to 32 or so, and run `repeat 1000 { build "" {forever {move; turn left}}}`. Before applying this PR, it should grind to a halt after a while. After this PR, it should keep running, albeit with lots of lag. Closes #42.
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Cap the maximum number of ticks per frame (arbitrarily) at 30, to prevent the "spiral of death" (see https://gafferongames.com/post/fix_your_timestep/). To see this in effect, go into Creative mode, crank up the ticks per second to 32 or so, then (for suitable definitions of `repeat` and `forever`) execute `repeat 1000 { build "" {forever {move; turn left}}}` Without this PR, it should eventually grind to a halt. With this PR, the game should keep running, though with lots of lag. Closes #42 .
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At the moment, Swarm is susceptible to the "spiral of death" described at https://gafferongames.com/post/fix_your_timestep/ : when the amount of computation we have to do for a frame takes longer than the amount of time allotted for the frame, it starts getting further and further behind. This could in theory be triggered either by a lot of robots doing a lot of computation, or by the user pushing the ticks/second rate too high. If this happens, each frame will take longer than the previous frame and the game will essentially grind to a halt as it tries futilely to catch up but only gets further and further behind.
There is a simple way to avoid this, which is simply to cap the maximum number of ticks per frame (based on my own experience so far, a cap of around 25 seems reasonable). When it hits the cap, the game will slow down: it will essentially be running at a slower ticks/second rate than requested. Perhaps we could signal this by e.g. drawing the ticks per second rate in red, or something like that.
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