Registering custom signals with multiple arguments

[arunvickram]

Hi everyone, I've been looking through the information trying to see how to create signals with multiple arguments, and I was wondering how to go about creating signals with arguments in Nim?

I know that something like

gdobj CharacterStats of Node:
  method init*() =
    self.addUserSignal("health_changed")

is somewhat the equivalent of the following GDScript:

extends Node

signal health_changed

I'm still unsure how to write the equivalent GDScript:

extends Node
signal health_changed(amount)

Thanks for all the help so far!

[zetashift]

I haven't done this before but according to : https://pragmagic.github.io/godot-nim/v0.5.4/godotapi/objects.html#addUserSignal,Object,string,Array
proc addUserSignal*(self: Object; signal: string; arguments: Array) {..}

you should be able to do or something like this atleast:

gdobj CharacterStats of Node:
  method init*() =
    let amount = 5
    self.addUserSignal("health_changed", newArray(amount.toVariant))

[arunvickram]

That's what I figured and hoping wouldn't be the case. I was hoping that at least you could do something like

self.addUserSignal("health_changed", newArray(VariantType.Int))

I'm still unsure whether or not the newArray passed to addUserSignal would contain elements such as 0.toVariant or whether the number passed into the newArray would really just be the numerical representation of the VariantType enum, like VariantType.Int = 1

[zetashift]

I actually don't know much about this either and googling this didnt get me far.
But: https://docs.godotengine.org/en/stable/tutorials/plugins/gdnative/gdnative-cpp-example.html#signals says:

Here we see a nice improvement in the latest version of godot-cpp 
where our register_signal method can be a single call first taking the signals name, 
then having pairs of values specifying the parameter name and type of each parameter 
we'll send along with this signal.

However I cannot read C++ haha.

[arunvickram]

It looks like this would require a change in the genType function to use Nativescript 1.1 and register signals along with registering methods

godot-nim/godot/nim/godotmacros.nim

Line 440 in f25c3c7

proc genType(obj: ObjectDecl): NimNode {.compileTime.} =

[arunvickram]

It would also likely require a change to parseType to parse custom signal declarations like this:

signal healthChanged(amount: int)

[endragor]

This is how you can do it:

self.addUserSignal("health_changed", newArray([{"amount": TYPE_INT}.toTable()]))

TYPE_xxx constants can be found in global_constants.nim. A small improvement could be to implement a toVariant/fromVariant conversion for a seq of pairs. Then the .toTable() part won't be necessary.

[geekrelief]

self.addUserSignal("health_changed", newArray([{"amount": TYPE_INT}.toTable()]))

hmm, I tried using this, and I get a type mismatch error for newArray since there isn't a proc that accepts Table.

This is how I've added a signal in the past. But it's pretty verbose:

  import godotapi / [global_constants]
  var arg0 = newDictionary()
  arg0["name".toVariant] = "amount".toVariant
  arg0["type".toVariant] = TYPE_INT.toVariant
  var args = newArray(arg0.toVariant) # each dictionary adds an argument
  self.addUserSignal("health_changed", args)

[endragor]

Trying changing array to sequence (add @). This should work:

self.addUserSignal("health_changed", newArray(@[{"amount": TYPE_INT}.toTable()]))

[arunvickram]

@endragor Does the register_signals method in the C++ version register them so that the signals are viewable in the Godot editor? If so, that's what I was alluding to and was wondering whether that would be a better way to go about it?

[geekrelief]

Trying changing array to sequence (add @). This should work:

self.addUserSignal("health_changed", newArray(@[{"amount": TYPE_INT}.toTable()]))

Yeah, that's not working either. Here's the truncated error.

Error: type mismatch: got <seq[Table[system.string, system.int64]]>
but expected one of:
proc newArray(arr: GodotArray): Array
  first type mismatch at position: 1
  required type for arr: GodotArray
  but expression '@[toTable([("amount", 2'i64)])]' is of type: seq[Table[system.string, system.int64]]
...

Looking at the code in arrays.nim, I don't see how newArray accepts a seq or a Table. The only proc that would make sense is for openarray[Variant], but the arguments would need to have toVariant called on it right?

In anycase, I just followed the docs for https://docs.godotengine.org/en/stable/classes/class_object.html#class-object-method-add-user-signal and that's how I arrived at the code that uses a Dictionary per argument with "name" and "type" keys. It would be nice to have a cleaner have a cleaner way to set this up, otherwise I'll write a macro.

[arunvickram]

@geekrelief this is the same error that I'm running into atm, which is partially why I suggested looking into calling register_signal in the same genType type call that registers the methods and the variables to be exported. I could be wrong, but it seems like that might be more idiomatic Godot thing to do.

[geekrelief]

@arundilipan Yeah, I hear. I've considered modifying stuff in godotmacros.nim for other things like allowing let variables for instance or other macros. But I've resorted to creating my own macros to call with methods/procs. We would need to modify parseType and genType to allow things other than var, proc, and methods.

I'll try playing around with it tomorrow.

[zetashift]

@geekrelief any code you could share I think it could come in handy for future people looking into these stuff.

EDIT: nvm I see the gdnim repo.

[geekrelief]

@zetashift Feel free to create issues on the gdnim repo if you have questions or ping me on discord. Been looking to share, but I'm not sure what's the best/appropriate way to reach out to our tiny godot-nim community.

[geekrelief]

Anyone have a suggestion on how to get nim to recognize this syntax?

signal my_signal(a:bool = true)

Nim is erroring at the '=' thinking my_signal is using an Object construction syntax when what we want is a proc syntax for default arguments. And it would be nice to have that for default arguments for signals to match gdscript.

signal my_signal(a:bool)

works fine gut no default arguments.

signal my_signal(a:bool):
  a = true

Works too, but not as pretty.

Edit:

signal my_signal(a = true, b:int)

Is another option, it produces an AST I can work with.