Fog via Constructive Solid Gemoetry

• Wikipedia: Constructive solid geometry
• Integrate OpenGL with Panda
• Transparent Object, that masks background
  

  drawBackground(C);
  glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
  render(RealWorld);
  glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
  render(Fog);

• csg.js and its docs (great) and demo
• constructive solid geometry using bsp
• Stack Overflow: How to create Constructive Solid Geometry in OpenGL / C++
• Constructive Solid Geometry with the Stencil Buffer
• csg c++/opengl lib