The Camera Background Images uses a alpha under blending. For alpha under blending to work correctly the framebuffer containing the result of the render engine needs to be active (`DefaultFramebufferList.default_fb`) and the source blend color needs to be premultiplied with alpha. Due to recent refactoring this wasn't the case and it seemed that the background image was drawn in front of the scene. This patch sets the correct state so it seems to be drawn behind the scene. Reviewed By: fclem Differential Revision: https://developer.blender.org/D6365