add load_shaders method

example.rb

@@ -14,6 +14,48 @@ class Example
     create_window
   end
 
+  def load_shaders
+    v_id = glCreateShader(GL_VERTEX_SHADER)
+    glShaderSource(v_id, <<-EOS)
+      attribute vec2 pos;
+      varying vec4 pos_i;
+
+      void main()
+      {
+        pos_i = vec4(pos, 0, 1);
+        gl_Position = pos_i;
+      }
+    EOS
+    glCompileShader(v_id)
+    unless glGetShaderiv(v_id, GL_COMPILE_STATUS)
+      raise glGetShaderInfoLog(v_id)
+    end
+
+    f_id = glCreateShader(GL_FRAGMENT_SHADER)
+    glShaderSource(f_id, <<-EOS)
+      varying vec4 pos_i;
+
+      void main()
+      {
+        gl_FragColor = pos_i;
+      }
+    EOS
+    glCompileShader(f_id)
+    unless glGetShaderiv(f_id, GL_COMPILE_STATUS)
+      raise glGetShaderInfoLog(f_id)
+    end
+
+    p_id = glCreateProgram()
+    glAttachShader(p_id, v_id)
+    glAttachShader(p_id, f_id)
+    glLinkProgram(p_id)
+    unless glGetProgramiv(p_id, GL_LINK_STATUS)
+      raise glGetProgramInfoLog(p_id)
+    end
+
+    glUseProgram(p_id)
+  end
+
   def create_window
     if @fullscreen
       @window.create(VideoMode.get_desktop_mode, TITLE, Style::Fullscreen)
@@ -22,6 +64,7 @@ class Example
     end
 
     glClearColor(1, 0.5, 0, 0)
+    load_shaders
   end
 
   def run