sdl_test.cr

class ShaderProgram

  def use
    print "in program.use.  id: "
    puts @id
    GL.use_program.call(@id)
  end

  def use
    print "in program.use.  id: "
    puts @id
    GL.use_program.call(@id)
    yield
    GL.use_program.call(0_u32)
  end

  def unuse
    GL.use_program.call(0_u32)
  end

end

SDL.init do

  puts "sdl is running"

  SDL::Window.new(title: "Crystal OpenGL Demo", width: 1920, height: 1080,
                  flags: LibSDL::WINDOW_OPENGL | LibSDL::WINDOW_FULLSCREEN_DESKTOP) do |window|
    running = true
    position_location = uninitialized LibGL::Int

    puts "now running"

    a = [ -1_f32,  1_f32, -1_f32 ]
    b = [ -1_f32,  -1_f32, 1_f32 ]
    c = [ 1_f32,  1_f32, 1_f32 ]
    d = [ 1_f32,  -1_f32, -1_f32 ]

    triangle = [
      a, c, b,
      a, b, d,
      b, c, d,
      c, a, d
    ].flatten

    #load shader source strings

    #create shader programs
    program = ShaderProgram.new("simple")
    program.compile
    program.bind
    program.link
    # aaaaa = 7 # if I uncomment, the triangles don't show up
                # BUT, if I use the non-block version of program.use, it all works either way.
    # So A)   define aaaaa, program.use do, No Work
    #    B) nodefine aaaaa, program.use do,    Work
    #    C)   define aaaaa, program.use,       Work
    #    D) nodefine aaaaa, program.use,       Work

    program.use do

      # ...
      
      # draw triangles to the screen
      LibGL.draw_arrays(LibGL::TRIANGLES, 0_u32, triangle.size/3)
      # ...

    end
  end
end