Minimal SDL2 & OpenGL stencil buffer example.mm

#include <SDL2/SDL.h>
#include "seal_quadColours_triangles.h"
#include "seal_texture.h"

int main( const int argc, const char * const argv[] )
{
  const int W = 320, H = 240;

  SDL_Init( SDL_INIT_VIDEO );
  /* Request a stencil buffer of at least 1bit per pixel. */
  SDL_GL_SetAttribute( SDL_GL_STENCIL_SIZE, 1 );
  SDL_Window *window = SDL_CreateWindow( "SDL2 & OpenGL (stencil buffer)", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, W, H, SDL_WINDOW_OPENGL );
  SDL_GLContext context = SDL_GL_CreateContext( window );

  glMatrixMode( GL_PROJECTION );
  glLoadIdentity();
  glOrtho( 0, W, 0, H, -1, 1 );
  glMatrixMode( GL_MODELVIEW );
  glClearColor( 0, 0, 0, 1 );
  glEnable( GL_STENCIL_TEST );
  glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );
  glEnable( GL_BLEND );
  glEnableClientState( GL_VERTEX_ARRAY );
  glEnableClientState( GL_COLOR_ARRAY );

  seal_QuadColours_Triangles quadColours( 1, 1, 1, 1 );
  seal_Texture *texture = new seal_Texture( "texture.png", 128, 128 );
  seal_Quad_Triangles geometryQuad( W / 2 - 64, H / 2 - 64, 128, 128 ), textureQuad;
  texture->p_GetSubTextureQuad( 0, &textureQuad );

  seal_Quad_Triangles maskGeometry;
  maskGeometry.p_SetTopLeftCorner( W / 2, H / 2 + 64 );     // Top
  maskGeometry.p_SetTopRightCorner( W / 2 + 64, H / 2 );    // Right
  maskGeometry.p_SetBottomRightCorner( W / 2, H / 2 - 64 ); // Bottom
  maskGeometry.p_SetBottomLeftCorner( W / 2 - 64, H / 2 );  // Left
  seal_QuadColours_Triangles maskColour( 1, 1, 1, 1 );

  bool quit = false;
  do
  {
    SDL_Event event;
    while( SDL_PollEvent( &event ))
      if( event.type == SDL_QUIT )
        quit = true;

    glClear( GL_STENCIL_BUFFER_BIT );
    glStencilFunc( GL_ALWAYS, 1 , 0xffffffff );
    glStencilOp( GL_REPLACE, GL_REPLACE, GL_REPLACE );
    glDisable( GL_TEXTURE_2D );
    glDisableClientState( GL_TEXTURE_COORD_ARRAY );
    glVertexPointer( 2, GL_FLOAT, 0, maskGeometry.m_coordinates );
    glColorPointer( 4, GL_FLOAT, 0, maskColour.m_rgba );
    glDrawArrays( GL_TRIANGLES, 0, 6 );
    glStencilFunc( GL_EQUAL, 1, 0xffffffff );
    glStencilOp( GL_KEEP, GL_KEEP, GL_KEEP );

    glEnable( GL_TEXTURE_2D );
    glEnableClientState( GL_TEXTURE_COORD_ARRAY );
    glClear( GL_COLOR_BUFFER_BIT );
    glVertexPointer( 2, GL_FLOAT, 0, geometryQuad.m_coordinates );
    glColorPointer( 4, GL_FLOAT, 0, quadColours.m_rgba );
    glTexCoordPointer( 2, GL_FLOAT, 0, textureQuad.m_coordinates );
    texture->p_Bind();
    glDrawArrays( GL_TRIANGLES, 0, 6 );
    SDL_GL_SwapWindow( window );
  }
  while( !quit );

  delete texture;

  SDL_GL_DeleteContext( context );
  SDL_DestroyWindow( window );
  SDL_Quit();
  return 0;
}