Fix Grass Patterns due to Bad PRNG Seeding#86
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themrdemonized merged 1 commit intothemrdemonized:all-in-one-vs2022-wpofrom Oct 13, 2024
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…ry and fix uniformity when values are 0
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Fix Grass Patterns due to Bad PRNG Seeding (cherry picked from commit 722d3d8)
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See this GAMMA Discord discussion and comparison for example:
https://discord.com/channels/912320241713958912/1279805292472832101/1295062734836338858
Basically: The seeding procedure before had too much symmetry (e.g. if
D.sx = AandD.sz = Bthen the configurationD.sx = BandD.sz = Awould produce the same seed value) and when either were 0 it would produce the same seed along the entire axis (in world coordinates).Using a 64-bit LCG iteration as a hash function, and combining
D.sxandD.szinto au64in this way removes symmetries and solves the 0 problem. More info on LCGs here:https://en.wikipedia.org/wiki/Linear_congruential_generator
https://www.pcg-random.org/posts/does-it-beat-the-minimal-standard.html (this is where I got the 64-bit constant from)