code: func StencilFuncSeparate(face uint32, xfunc uint32, ref int32, mask uint32) {
  	C.glowStencilFuncSeparate(gpStencilFuncSeparate, (C.GLenum)(face), (C.GLenum)(xfunc), (C.GLint)(ref), (C.GLuint)(mask))
  }
docs: // set front and/or back function and reference value for stencil testing