Perfecting anti-aliasing on signed distance functions
6 comments
·August 4, 2025NohatCoder
Reminds me that I found an alternative way of sampling an SFD:
First take a sample in each corner of the pixel to be rendered (`s1 s2 s3 s4`), then compute:
coverage=0.5 + (s1+s2+s3+s4)/(abs(s1)+abs(s2)+abs(s3)+abs(s4))/2
Relative to the standard method it is expensive to calculate. But for a modern GPU it is still a very light workload to do this once per screen pixel.
shiandow
Technically that only requires calculating one extra row and column of pixels.
It is indeed scale invariant but I think you can do better, you should have enough to make it invariant to any linear transformation. The calculation will be more complex but that is nothing compared to evaluating the SDF
brookman64k
Would that be done in two passes? 1. Render the image shifted by 0.5 pixels in both directions (plus one additional row & column). 2. Apply above formula to each pixel (4 reads, 1 write).
mxfh
The minute black area on the inner part of the sector getting perceptually boosted with the same ramp width like the outer area is effectively how an outline on a shape would behave, not two shapes with no stroke width. I would expect the output brightness should scale with the volume/depth under a pixel in the 3d visualization.
Is this intentional? To me this is an opiniated (aka artistic preference) feature preserving method not the perfect one.
Btw the common visualization has a source and an author:
https://iquilezles.org/articles/distfunctions2d/ https://www.shadertoy.com/playlist/MXdSRf
Retr0id
> The minute black area on the inner part of the sector
I'm not grasping what you're referring to here.
A very good example of SDF thinking, using signed distance fields in shaders. Both shaders and SDF are new to me and very interesting. Another example of what is being done is MSDF here: https://github.com/Chlumsky/msdfgen.