[swift-users] Swift can’t compile code with OpenGL function pointers

[Kelvin Ma]

There are hundreds of gl functions… I have to rewrite the signatures for
all of them??

On Thu, Mar 30, 2017 at 11:31 AM, Joe Groff <jgroff at apple.com> wrote:

>
> > On Mar 30, 2017, at 7:47 AM, Kelvin Ma via swift-users <
> swift-users at swift.org> wrote:
> >
> > OpenGL functions are loaded at runtime by a function loader (like GLFW).
> They’re defined in a header but obviously they don’t have definitions at
> compile time so it causes a slew of linker errors when I try to build
> >
> >     error: undefined reference to 'glEnable'
> >     error: undefined reference to 'glBlendFunc'
> >     error: undefined reference to 'glClearColor'
> >     clang: error: linker command failed with exit code 1 (use -v to see
> invocation)
> >     ...
> >
> > How do I build programs that use OpenGL functions?
>
> If the functions are exported by the OpenGL library you're linking
> against, then you may need to just use -lGL to link against it. That's not
> likely to be portable, though, since implementations vary in what they
> statically export. The macro metaprogramming used by GLFW and other
> libraries to dynamically load GL entry points is probably not going to get
> picked up by Swift's C importer, so you'd need to roll your own solution.
> Something like this might work as a start:
>
> func loadGLFunction<T>(name: String) -> T {
> #if os(macOS)
>   return unsafeBitCast(dlsym(RTLD_DEFAULT, name), to: T.self)
> #elseif os(Linux)
>   return unsafeBitCast(glXGetProcAddress(name), to: T.self)
> #elseif os(Windows)
>   return unsafeBitCast(wglGetProcAddress(name), to: T.self)
> #endif
> }
>
> enum GL {
>   static let begin: @convention(c) (GLenum) -> Void =
> loadGLFunction("glBegin")
>   static let end: @convention(c) () -> Void = loadGLFunction("glEnd")
>   /*etc*/
> }
>
> -Joe
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