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Replace AHash with a good sequence for entity AABB colors #9175

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merged 4 commits into from
Jul 21, 2023
Merged

Replace AHash with a good sequence for entity AABB colors #9175

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129b657
Use a good sequence for entity AABB colors
nicopap Jul 16, 2023
a7df420
Use index u32 over to_bits
nicopap Jul 16, 2023
b18adef
Use multiplication over division
nicopap Jul 16, 2023
5b41bdc
Merge gold_kronecker & color_from_entity
nicopap Jul 21, 2023
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22 changes: 14 additions & 8 deletions crates/bevy_gizmos/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -232,15 +232,21 @@ fn draw_all_aabbs(
}
}

fn gold_kronecker(bits: u64) -> f32 {
// from https://extremelearning.com.au/unreasonable-effectiveness-of-quasirandom-sequences/
//
// See https://en.wikipedia.org/wiki/Low-discrepancy_sequence
// Map a sequence of integers (eg: 154, 155, 156, 157, 158) into the [0.0..1.0] range,
// so that the closer the numbers are, the larger the difference of their image.

// (u64::MAX / Φ) rounded down
// see https://probablydance.com/2018/06/16/fibonacci-hashing-the-optimization-that-the-world-forgot-or-a-better-alternative-to-integer-modulo/
const FRAC_U64MAX_GOLDEN_RATIO: u64 = 11400714819323198485;
const RATIO_360: f32 = u64::MAX as f32 / 360.0;
bits.wrapping_mul(FRAC_U64MAX_GOLDEN_RATIO) as f32 / RATIO_360
}
fn color_from_entity(entity: Entity) -> Color {
use bevy_utils::RandomState;
const U64_TO_DEGREES: f32 = 360.0 / u64::MAX as f32;
const STATE: RandomState =
RandomState::with_seeds(5952553601252303067, 16866614500153072625, 0, 0);

let hash = STATE.hash_one(entity);
let hue = hash as f32 * U64_TO_DEGREES;
Color::hsl(hue, 1., 0.5)
Color::hsl(gold_kronecker(entity.to_bits()), 1., 0.5)
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}

fn aabb_transform(aabb: Aabb, transform: GlobalTransform) -> GlobalTransform {
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