add and use gl3w

Rakefile.rb

@@ -9,7 +9,7 @@ NAME = "freetype2gl3"
 task :default do
   Rscons::Environment.new do |env|
     env.build_root = "build"
-    env["LIBS"] += ["SDL2", "GL"]
+    env["LIBS"] += ["SDL2", "GL", "dl"]
     env.Program("^/#{NAME}", Dir["*.{cc,c}"])
   end
 end

freetype2gl3.cc

@@ -1,6 +1,5 @@
 #include <SDL2/SDL.h>
-#include <GL/gl.h>
-#include <GL/glu.h>
+#include "gl3w.h"
 
 #define WIDTH   500
 #define HEIGHT  500
@@ -41,6 +40,20 @@ int main(int argc, char *argv[])
 
     SDL_GLContext gl_context = SDL_GL_CreateContext(window);
 
+    if (gl3wInit() != 0)
+    {
+        printf("Failed to gl3wInit()\n");
+        SDL_Quit();
+        return 2;
+    }
+
+    if (!gl3wIsSupported(3, 0))
+    {
+        printf("OpenGL 3.0 is not supported!\n");
+        SDL_Quit();
+        return 2;
+    }
+
     init();
     display(window);
     SDL_Event event;