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Comment by tehsauce | Hacker News Reader

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tehsauce·

Anyone else confused by the end where it mentions SDFs, says

> if you write JavaScript, I think you are already familiar with the idea:

then shows sorting an array with pairs of elements a and b in javascript and says

> And we are calling it “signed distance from b to a”.

what do SDFs have to do with sorting an array?

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I think what the author's getting at is that the function you pass to JavaScript .sort() just returns a number — not special sentinel values — which represents the relative order of two items in the array. By calling that function strategically from a loop, .sort() can sort the array.

Similarly, an SDF returns a number that represents how far a point in 3D space is from an object's surface. And, by calling that function strategically from a loop, you can draw a 3D scene using only that function.

The difference is that .sort() only uses the sign of the return value and ignores the magnitude. Ultimately, all the sort algorithm needs is the boundary condition, e.g. a comparator. The SDF equivalent needs both the sign (is this point inside or outside of this implicit surface), alongside the magnitude, to determine the closest hit.

I don't see how they're that interlinked other than saying that signed distance functions are a subset of comparators.

Yeah, I've done a lot with SDF, and I don't know what they mean. I guess SDFs and ordering are tengentially related..

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