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1547 :: resolved: insert the params in OpenGL wrapper

• balezin (orginal) [2015-08-17T15:43:48+02:00] view original

  In the opengl wrapper (git://github.com/nim-lang/opengl) present the code:

  proc glLightfv(light: GLenum, pname: GLenum, params: ptr GLfloat) {.importc.}
  Run

  How do I declare the last parameter "params: ptr GLfloat" with 4 float parameters in the Nim for use this procedure? In the Python it was:

  Run

  In the C it looks like this:

  GLfloat sp[4] = {1.45, 1.45, 1.30, 1.00};
  glLightfv(GL_LIGHT0, GL_DIFFUSE, sp);
  Run

  ---

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  [RESOLVED:] In the Nim:

  var
    mySet: array[0..3, GLfloat] = [0.5'f32, 0.5'f32, 0.5'f32, 1.0'f32]
    param_set: ptr = mySet[0].addr
  
  glLightfv(GL_LIGHT0, GL_DIFFUSE, param_set)
  Run

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• EXetoC (orginal) [2015-08-17T16:10:57+02:00] view original

  I never generated high-level signatures based on the spec unfortunately. The thing with C is that it conflates pointers with arrays, but the typing is stronger in nim, so in this case you have to create either a array or seq var (var params = [...] and var params = @[...] respectively), and then pass in params[0].addr. params.addr is identical in the case of arrays, but I prefer to do the former just to prevent mistakes.

  A var statement is necessary since it's not possible to create a var expression and take the address of that.

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• Quikli (orginal) [2015-08-18T04:33:11+02:00] view original

  Nim is expecting a pointer to a GLfloat, not a pointer to an array or seq of GLfloats. So you want to take the address of the first element:

  import opengl
  loadExtensions()
  type
    ColorChannel = enum
      r, g, b, a
  var p: array[ColorChannel, GLfloat]
  p[r] = 0.3
  p[g] = 0.9
  p[b] = 0.3
  p[a] = 1.0
  glLightfv(GL_LIGHT0, GL_DIFFUSE, addr(p[r]))
  Run

  This compiles, but errors at runtime. I don't know the OpenGL API, but I'm assuming the runtime error is because we don't have an OpenGL context within which to draw?

  Error: unhandled exception: OpenGL error: invalid operation [GLerror]

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• balezin (orginal) [2015-08-18T04:54:19+02:00] view original

  Quikli, аbout OpenGL context you are right, bat in this case it does not matter. Thank you for reply.

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• Kerp (orginal) [2015-08-18T07:41:21+02:00] view original

  try this i think this will work but i did not try it, i will check for you edit: I tried it and made some adjustments this compiles but i don't know if it works for your program.

  
  
  var d : ptr = j[0].addr
  var c : ptr = p[0].addr
  
  glLightfv(GL_LIGHT0, GL_AMBIENT, d)
  
  glGetLightfv(GL_LIGHT0, GL_AMBIENT, c) 
  Run

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• balezin (orginal) [2015-08-18T08:01:39+02:00] view original

  to Kerp: you a right too, thank you.

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• Kerp (orginal) [2015-08-18T08:35:11+02:00] view original

  you may just have to wait till someone else with more experience comes along.. i'm still a nimlet :)

  but it looks like the first parameter is getting its value maybe change the second and it will work?

  try a variation of putting p into glGetLightFv

  maybe try

  
   glGetLightfv(GL_LIGHT0, GL_AMBIENT, p[0].addr)
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  or

  
   glGetLightfv(GL_LIGHT0, GL_AMBIENT, p.addr)
  
  Run

  trial and error sometimes works! maybe try

  
   glGetLightfv(GL_LIGHT0, GL_AMBIENT, p)
  Run

  or

  
   glGetLightfv(GL_LIGHT0, GL_AMBIENT, p[])
  Run

  just keep trying!

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• balezin (orginal) [2015-08-18T08:50:27+02:00] view original

  This code is work fine:

  var mySet: array[0..3, GLfloat] = [0.5'f32, 0.5'f32, 0.5'f32, 1.0'f32]
  glLightfv(GL_LIGHT0, GL_DIFFUSE, mySet[0].addr)
  Run

  and this [for aesthetes] too:

  var
    mySet: array[0..3, GLfloat] = [0.5'f32, 0.5'f32, 0.5'f32, 1.0'f32]
    param_set: ptr = mySet[0].addr
  
  glLightfv(GL_LIGHT0, GL_DIFFUSE, param_set)
  Run

  Thank for all!

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