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1628 :: importc and variant types

• sstirlin (orginal) [2015-09-11T18:12:50+02:00] view original

  I'm playing with adding HTML5 CanvasObj bindings to the dom module, but I've encountered some javascript dynamic nastiness.

  Here is a snippet of the bindings that I'm trying:

  RenderingContext* {.importc.} = object of RootObj
      fillStyle*: cstring
      fillRect*: proc (x: int, y: int, width: int, height: int) {.nimcall.}
      #  blah blah more stuff
  
  CanvasElement* = ref CanvasObj
  CanvasObj {.importc.} = object of ElementObj
      getContext*: proc (contextType: cstring): RenderingContext {.nimcall.}
      # blah blah more stuff
  Run

  Here's the problem. That fillStyle property in Javascript is actually not just a string. It can take three different types according to the documentation here:

  https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/fillStyle

  How do I handle this kind of variant-like binding? Thanks

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• yglukhov (orginal) [2015-09-11T20:37:59+02:00] view original

  You can try this:

  proc `fillStyle=`(c: CanvasElement, value: MyType1 or MyType2 or MyType3) =
    {.emit: "`c`.fillStyle = `value`;".}
  Run

  Note that you may need a dedicated proc overload for a type that needs implicit converting. E.g. for cstring, because string literals will not convert to it.

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• sstirlin (orginal) [2015-09-12T00:34:26+02:00] view original

  My mind just exploded with how awesome this is. For some reason the emit pragma isn't working, but the approach is cool. Here's what I have now (just to see if I can get the simplest thing working):

  type
    RenderingContext* {.importc.} = object of RootObj
      fillRect*: proc (x: int, y: int, width: int, height: int) {.nimcall.}
  
  proc `fillStyle=`*(c: RenderingContext, value: cstring) =
    {.emit: """`c`.fillStyle = `value`;""".}
  Run

  The {.emit: doesn't seem to be working, however. Here's how the generated js looks:

  function fillstyleHEX3D_31125(c_31127, value_31128) {
      
      var F={procname:"dom.fillStyle=",prev:framePtr,filename:"c:\\nim\\lib\\js\\dom.nim",line:0};
      framePtr = F;
      rawEcho(cstrToNimstr("haha"));
      framePtr = framePtr.prev;
  }
  
  // blah blah ...
  
  var canvas_32003 = document.getElementById("canvas");
  
  if (!((canvas_32003 == null))) {
      
      F.line = 6;
      var ctx_32016 = canvas_32003.getContext("2d");
      fillstyleHEX3D_31125(ctx_32016, "blue");
      ctx_32016.fillRect(10, 10, 75, 50);
      rawEcho(cstrToNimstr("haha"));
  
  }
  Run

  So it still synthesized some "fillstyle" function instead of emitting the literal string. Any ideas?

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• sstirlin (orginal) [2015-09-12T01:10:40+02:00] view original

  OK, {.emit: doesn't seem to be working at all for the js backend on 11.2. Then I found that support is pretty recent:

  https://github.com/nim-lang/Nim/pull/3147

  I'll check against master

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• yglukhov (orginal) [2015-09-12T18:30:25+02:00] view original

  True. Emit for js is pretty recent. Previously asm stmt was used for that stuff.

  proc foo() =
    asm """
    alert("foo");
    """
  Run

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• sstirlin (orginal) [2015-09-12T19:31:30+02:00] view original

  I confirmed that emit works for js in master (which I assume will be 11.3 at some point). This solution works great! Thanks.

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