Mirror of forum.nim-lang.org

2638 :: Problems trying to wrap a single header file library

• def_pri_pub (orginal) [2016-11-28T01:37:42+01:00] view original

  I'm working on porting over some ray tracing code from a C++ project. So far things have been fine, but they used this library called stb_image.h to load in textures.

  I thought I would try to create a wrapper for the single function that is used "stbi_load()"

  So far I've got this (filename "stb_image.nim")

  # This file is a wrapper of a subset for the "stb_image.h" library that is
  # needed for the raytracer
  
  # Required before including the stb_image.h header
  {.emit: """
  #define STB_IMAGE_IMPLEMENTATION
  """.}
  
  # Internal function
  proc stbi_load(filename: cstring; x, y, comp: var cint; req_comp: cint): cstring
    {.importc: "stbi_load", header: "stb_image.h".}
  
  
  ## External function (the Nim friendly version)
  proc stbi_load*(filename: string; x, y, comp: var int; req_comp: int): seq[uint8] =
    var
      width: cint
      height: cint
      comp2: cint
      pixelData: seq[uint8]
    
    let data = stbi_load(filename.cstring, width, height, comp2, req_comp.cint)
    
    # Set the data
    x = width.int
    y = width.int
    comp = comp2.int
    
    newSeq(pixelData, x * y)
    # TODO set the pixelData
    
    return pixelData
  
  Run

  I seem to be fine, until I compile and get this:

  
  CC: stb_image
  Error: execution of an external compiler program 'gcc -c  -w  -I/home/ben/bin/Nim/lib -o nimcache/stb_image.o nimcache/stb_image.c' failed with exit code: 1
  
  nimcache/stb_image.c:10:23: fatal error: stb_image.h: No such file or directory
  compilation terminated.
  Run

  I have the stb_image.h file right alongside the nim one. What should I do here?

  Also, do you think the return type cstring (for the internal function) is fine? stb_image() returns an unsigned char *. I figured casting it to a seq[uint8] should be fine.

---

• jlp765 (orginal) [2016-11-28T07:43:56+01:00] view original

  Have a look at how it was done for this Urhonimo wrapper

---

• def_pri_pub (orginal) [2016-11-29T01:32:03+01:00] view original

  Alright, I got it to work. The trick was three things:

  Change the emit to this:

  # Required before including the stb_image.h header
  {.emit: """
  #define STB_IMAGE_IMPLEMENTATION
  #include "stb_image.h"
  """.}
  Run

  Remove the "header," pragma and add a "noDecl" one:

  # Internal Function
  proc stbi_load(filename: cstring; x, y, comp: var cint; req_comp: cint): cstring
    {.importc: "stbi_load", noDecl.}
  
  Run

  Tell the compiler where to look for stb_image.h. In my case that file was right alongside stb_image.nim, so for me it was:

  
  --cincludes:.
  Run

---