Option to start the game paused

[xsebek]

Is your feature request related to a problem? Please describe.

Sometimes (#2064), I need to debug the first tick of the game.
That is hard because the game starts in a running state.

Describe the solution you'd like

Add command line option --paused to initialize the game state with the runState == ManualPaused.

Describe alternatives you've considered

I would not mind writing --debug=startPaused from #1324.

Starting with the game paused could be useful for competitive play, but probably not a good default.

[xsebek]

I tried to initialize the game while paused and was surprised it did not do anything. Apparently, other game state initialization functions use the scenario description. I wonder if the first game state is used outside of tests.

[xsebek]

@byorgey to test this, I set the scenario code to always start paused:

diff --git a/src/swarm-engine/Swarm/Game/State/Initialize.hs b/src/swarm-engine/Swarm/Game/State/Initialize.hs
index 5e716353..86715151 100644
--- a/src/swarm-engine/Swarm/Game/State/Initialize.hs
+++ b/src/swarm-engine/Swarm/Game/State/Initialize.hs
@@ -88,6 +88,7 @@ pureScenarioToGameState scenario theSeed now toRun gsc =
   gs = initGameState gsc
   preliminaryGameState =
     gs
+      & temporal . runStatus .~ ManualPause
       & robotInfo %~ setRobotInfo baseID robotList'
       & creativeMode .~ scenario ^. scenarioOperation . scenarioCreative
       & winCondition .~ theWinCondition

This gets to a really strange state where the side panels are empty, and the goal is not yet shown, but REPL works:

After one step with C-o, the panels load, and the goal modal pops up.

[kostmo]

Not quite the same as pausing, but sometimes for debugging I have started the game at a very slow speed, e.g.:

scripts/play.sh -i Tutorials/move --autoplay --speed -3

[xsebek]

Thanks for the tip @kostmo !

I will try that out, though I would expect speed 0 to mean 0 ticks per second.

[byorgey]

Speed n means 2^n ticks per second. We should improve the help text to make that clearer. Right now it says "Initial game speed multiplier" which seems ambiguous at best.

[noahyor]

This gets to a really strange state where the side panels are empty, and the goal is not yet shown, but REPL works.

@xsebek, This is because the Inventory and Info panels update on Frame events, which causes this strange behavior.

I had to deal with this when I was integrating Swarm with Termite, because I forgot to spawn a thread which sends Frame events.

[xsebek]

Thanks for the info, @noahyor; I will file a separate Issue to update the panels at the start. 👍