Valve has made Dota 2's Direct3D to OpenGL translation layer open source. This is the piece of code that allows Valve to take a standard DirectX Windows game that uses the Source engine (Dota 2 ...

With little fanfare, Valve has published the source to ToGL, a translation layer to support a subset of the Direct3D 9 API on OpenGL systems. ToGL is a component of the company's Source 3D engine.