title: Add stroke to object in OpenGL using GLKit
body: <p>I'm drawing some objects to a view in my application using OpenGL with GLKit. I have been trying to add a stroke to one of the objects I'm drawing, but I can't figure out a good way to do that. I could probably add a stroke using a texture or by drawing lines over the object, but those don't sound like good/smart methods. What is the usual method to draw an object with a stroke?</p>
  
  <p>This is the code I'm currently using (<code>modelViewMatrix</code> and <code>vertices</code> are defined elsewhere):</p>
  
  <pre><code>GLKBaseEffect *effect = [[GLKBaseEffect alloc] init];
  effect.useConstantColor = YES;
  effect.constantColor = kPlayerColor;
  effect.transform.projectionMatrix = modelViewMatrix;
  [effect prepareToDraw];
  
  glEnableVertexAttribArray(GLKVertexAttribPosition);
  glVertexAttribPointer(GLKVertexAttribPosition, 2, GL_FLOAT, GL_FALSE, 0, vertices);
  
  glDrawArrays(GL_TRIANGLE_STRIP, 0, sizeof(vertices) / sizeof(vertices[0]));
  glDisableVertexAttribArray(GLKVertexAttribPosition);
  </code></pre>
  
  <p>In the following picture you can see what I currently draw (on the left) and what I would like to draw (on the right):</p>
  
  <p><img src="https://i.stack.imgur.com/cgFnM.png" alt="Images with (right) and without stroke (left)"></p>
  
  <p>So basically all I'd like to do is add a stroke (in this case black) to an object. Not all objects are as simple as this example.</p>
  
  <p>Summarized my question is: how do draw an object <strong>with stroke</strong> using OpenGL?</p>