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7086 :: best way to store key definition for a game

• jseb (orginal) [2020-11-13T12:13:56+01:00] view original

  Hello,

  I'm reading this tutorial: https://hookrace.net/blog/writing-a-2d-platform-game-in-nim-with-sdl2/

  He is using hardcoded keys like this:

  type Input {.pure.} =
    enum none, left, right, up, down, jump, restart, quit
  
  proc toInput(key: Scancode): Input =
    case key
    of SDL_SCANCODE_A: Input.left
    of SDL_SCANCODE_D: Input.right
    # etc…
    else: Input.none
  
  proc handleInput(game: Game) =
    var event = defaultEvent
    while pollEvent(event):
      case event.kind
      of KeyDown:
        game.inputs[event.key.keysym.scancode.toInput] = true
      # etc…
      else:
        discard
  
  Run

  Ok that's nice, but i want to be able to redefine inputs, for example SDL_SCANCODE_LEFT for Input.left.

  I guess of course i have to treat this in ToInput, but what should i use to store and compare ? Tuples , Arrays, Objects … ?

  Thank you.

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• PMunch (orginal) [2020-11-13T12:42:19+01:00] view original

  Depends a bit on how you want to optimise this. SDL keycodes are an enum with values in the range 0-512. What you could do is have an var mapping = array[Scancode.low.int..Scancode.high.int, Input] and then register your inputs like this: mapping[SDL_SCANCODE_A.int] = left. Since none is the first value of the Input enum it is also the default value, so a looking in mapping for a key that isn't mapped would return none. Then your toInput would simply be a lookup in this array, and to remap a key you can simply do the "Press key to bind" and store the input at whatever scancode you got.

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• enthus1ast (orginal) [2020-11-13T13:37:23+01:00] view original

  You can also use a table for this, see how I've done it here: https://github.com/enthus1ast/muk/blob/mukd/src/keybinding.nim

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• ynfle (orginal) [2020-11-13T15:38:47+01:00] view original

  Being as they are an ordinal type, you can just use them directly without have to convert them to an int

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• jseb (orginal) [2020-11-13T19:32:27+01:00] view original

  Thank you, both techniques are interesting (array and table). I think i try the array one, even if i need to loop it entirely for getting assigned keys.

  Thank you for explaining, coming from Lua i know only tables, tables and tables for solving everything !

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• ElegantBeef (orginal) [2020-11-13T23:04:17+01:00] view original

  You can do one better and just use the enumType as the size var mapping: array[ScanCode, Input]

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• landerlo (orginal) [2020-11-13T23:56:28+01:00] view original

  I like this encoding for enums. Sadly Scancode is not an ordinal, if we filled the gaps to make it an ordinal, we could have an even better syntax and use sets with them:

  var mapping: array[Scancode, Input]
  
  mapping[SDL_SCANCODE_A] = left
  mapping[SDL_SCANCODE_D] = right
  
  import std/packedsets      # Merged to devel today
  var mappedCodes: PackedSet[Scancode]
  
  for c in ScanCode:
    if mapping[c] != none: mappedCodes.incl(c)
  
  echo mappedCodes  # prints: "{SDL_SCANCODE_A, SDL_SCANCODE_D}"
  Run

  I think for these C enum compat cases we should provide a macro to fill the undefined holes with some hidden unknown_xxxx values, so we can use them as ordinals.

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• landerlo (orginal) [2020-11-14T00:01:23+01:00] view original

  Scancode is not an Ordinal because it has holes, so in recent versions of Nim that doesn't work. I think we should provide a macro to bridge this, see my post above.

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• jseb (orginal) [2020-11-14T20:12:55+01:00] view original

  Well it seems that it works for all of you, but not for me…

  Look what i get (from INim for sample purpose, but i have the same error with a regular compilation of my source):

  
  👑 INim 0.6.1
  Nim Compiler Version 1.4.1 [Linux: amd64]
  nim> import sdl2
  nim> type Input {.pure.} = enum none, left, right, up, down, jump, restart, quit
  nim> var mapping:array[ScanCode, Input]
  Error: ordinal type expected
  Run

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• nucky9 (orginal) [2020-11-14T21:45:26+01:00] view original

  You can use:

  var mapping: array[SDL_NUM_SCANCODES.int, Input]
  Run

  and access with

  mapping[SDL_SCANCODE_A.int].
  Run

  I don't understand why

  var mapping: array[Scancode, Input]
  Run

  won't work though, since it works if you try to use it in the the keymappings.nim file (where Scancode is defined). But, if you import or include keymappings.nim into another file, the compiler no longer recognizes the Scancode enum as being ordinal. Seems like a weird bug.

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• nucky9 (orginal) [2020-11-14T21:55:08+01:00] view original

  Ok, it's because the Scancode enum has holes, but I still don't understand how if you are using it from the file it is defined in or via import/include, it changes whether the compiler considers it ordinal

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• SolitudeSF (orginal) [2020-11-14T22:00:11+01:00] view original

  won't work though, since it works if you try to use it in the the keymappings.nim file (where Scancode is defined). But, if you import or include keymappings.nim into another file, the compiler no longer recognizes the Scancode enum as being ordinal if you try this from within that file. Seems like a weird bug.

  why does it work in keymappings.nim? its not ordinal

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• nucky9 (orginal) [2020-11-14T22:11:30+01:00] view original

  Yeah, it doesn't - it just wasn't being linted - my mistake! So, Scancode has holes, isn't ordinal and won't work.

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