 However these algorithms are generally still too computationally expensive for real time rendering (even though specilized HW exists, such as Nvidia RTX) and require a different rendering approach from typically used rasterization.Reflections on planar surfaces, such as planar mirrors or water surfaces, can be computed simply and accurately in real time with two pass rendering — one for the viewer, one for the view in the mirror, usually with the help of stencil buffer.Some older video games used a trick to achieve this effect with one pass rendering by putting the whole mirrored scene behind a transparent plane representing the mirror.