If we built a ray-tracing engine that imitated that specific model - i.e. That bounce can be specular where it changes direction - either through a reflection or refraction - or it can be diffuse where it scatters in all directions. In nature, rays of light are emitted from a light source. The best way to start to explore ray tracing is to start by observing nature. But methods like photon maps were invented because computing caustics from pure ray tracing is a big challenge. Many renderers have used something called “photon mapping” but, traditionally, those methods have been very complicated to use - and if not set up correctly, can be very slow to render or simply look very bad (or both!). There are some brute-force methods that can work, but generally they either take way too long or take a huge amount of shortcuts that end up giving you only a small fraction of the actual caustic contribution. The truth is that the way that we have been calculating caustics for years has been very complicated. But before we discuss how we fake it, let’s explain why we fake it. You might be wondering: If we’ve been ignoring caustics for so long, why do we get renders that look believable? In short: Caustics have been faked for years.
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