Rendering Line Lights

Within the arsenal of lights provided by game engines, the most popular are punctual lights such as point, spot or directional because they are cheap. On the other end, area lights have recently produced incredible techniques such as Linearly Transformed Cosines and other analytic approximations. I want to talk about the line light.

Update [04/09/2020] When I originally wrote the article there were no public images showing Jedi or lightsabers so I couldn’t make the connection (though a clever reader could have concluded what they might be for!) I can finally show this work off as it’s meant to be.

In Unreal Engine 4, modifying ‘Source Length’ on a point light elongates it as described in this paper. It spreads the intensity along the length so a longer light becomes perceptually dimmer. Frostbite also has tube lights, a complex implementation of the analytical illuminance emitted by a cylinder and two spheres. Unity includes tube lights as well in their HD Render Pipeline (thanks Eric Heitz and Evegenii Golubev for pointing it out) based on their LTC theory, which you can find a great explanation and demos for here. Guerrilla Games’ Decima Engine has elongated quad lights using an approach for which they have a very attractive and thorough explanation in GPU Pro 5’s chapter II.1, Physically Based Area Lights. This is what I adapted to line lights.

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