This is @KryptoScratcher 's triangle fill which I and lots of other 3D scratchers use in their projects due to it demonstratable being the fastest triangle fill. For some reason there wasn't a nice interactive demo for it, so I decided to make one. You can see that it fills the first green incircle, then moves out to blue, pink, yellow, and green layers, getting geometrically thinner as it goes. Each layer is such that the inner triangle formed by it barely overlaps the previous layer's outer triangle (in the direction of the most acute angle in the triangle) What separates this from other similar fills is that it will early exit when the current layer is thinner than the resolution, which saves quite a bit of computation on small triangles. I'm using the mathematically correct version which avoids artifacts, but the version used in many 3D engines often skips the last layer to save time, but this causes small gaps, and thin triangles render wrong. This GeoGebra applet shows how to derive the main part of this fill https://www.geogebra.org/classic/vbtfd6xv
