title: OpenGL / SDL2 : stencil buffer bits always 0 on PC
body: <p>I'm writing an app using SDL2 / OpenGL, and doing some stencil operations.</p>
  
  <p>Everything works as expected on Mac, however on PC the stenciling doesn't work.</p>
  
  <p>Upon closer inspection I realized that the following code provides different outcomes on my Mac and PC:</p>
  
  <p>SDL_Init(SDL_INIT_VIDEO);</p>
  
  <p>SDL_GL_SetAttribute( SDL_GL_STENCIL_SIZE, 8 );</p>
  
  <p>SDL_CreateWindow( ... );</p>
  
  <p>SDL_CreateRenderer( ... )</p>
  
  <p>... do stuff ...</p>
  
  <p>When I print out the stencil bits ( SDL_GL_STENCIL_SIZE ) on Mac I get 8. When I do the same on PC, I get 0.</p>
  
  <p>The same happens whether I run it on an actual PC, or on a PC emulator on the Mac.</p>
  
  <p>What am I missing? How can I force SDL2 to request a context with a stencil buffer?</p>
  
  <p>It looks to me like the Mac's OpenGL implementation has different defaults than the PC one, so I'm probably forgetting to do something to specifically request a stencil buffer, but I can't find any good information online ... </p>
  
  <p>Help ^_^' ?</p>