Adding the GLContext class.

[linkpy]

Nothing much to say.

I'm quiet new in Crystal, so fell free to give suggestions and critics about my code.

[ysbaddaden]

Thank you for trying out OpenGL in SDL.

Can you run crystal tool format src/context.cr, so the code is formatted in the expected way (2 spaces indentation, ...)?

Overall, you can remove most type definitions, for example replace w : Window with a descriptive window variable name. You can also remove most explicit return, since all methods implicitely return the latest expression.

[ysbaddaden]

You may just do the following; Crystal automatically transforms nil to a NULL pointer, and specifying types is optional.

def self.load_library(path)
  return if @@initialized
  @@initialized = true

  if LibSDL.gl_load_library(path) == 0
    raise Error.new("SDL_GL_LoadLibrary")
  end
end

[ysbaddaden]

Yes, we shouldn't have to deal with C pointers in Crystal. Can you point me to some usage examples?

[linkpy]

SDL::GLContext.load_library( "path/to/my/gl/lib" )
# This is here I don't know how to do (i'm not even sure it's correct code) :
clear_color = SDL::GLContext.proc_address(Void, Float, Float, Float, Float)( "glClearColor" )
# clear_color would be of type `Proc(Void, Float, Float, Float, Float)`

[ysbaddaden]

You must cast the void pointer to a proc, something like:

clear_color = LibSDL.gl_get_proc_address("glClearColor")
  .as(Pointer(Float32, Float32, Float32, Float32 ->))
  .value
clear_color.call(0_f32, 0_f32, 0_f32, 0_f32)

I'm not sure this is required, thought. We can initialize a GL context in SDL then simply call GL functions, can't we? That way we wouldn't need to load libraries nor dynamically link symbols at runtime.

[ysbaddaden]

We can use a getter/setter here:

def self.swap_interval
  LibSDL.gl_get_swap_interval
end

def self.swap_interval=(interval)
  unless LibSDL.gl_set_swap_interval(interval) == 0
    raise Error.new("SDL_GL_SetSwapInterval")
  end
  interval
end

[linkpy]

After some tries I got something (but I can't really try it) :

def self.get_proc_address( name )
  # Current implementation, nothing changes here but we need to keep this
  # function.
end

macro []( name, *types )
  Proc( {{*types}} ).new( SDL::GLContext.get_proc_address( {{name}} ), Pointer(Void).null )
end

# And we should it this macro like this :
clear_color = SDL::GLContext[ "glClearColor", Void, Float, Float, Float, Float ]

I found it a bit weird, but we don't need to use the [] operator, we can use proc_address, or anything else that can fit our needs.