brep_render/
color.rs

1//! Stable per-solid display colors + color-space helpers.
2//!
3//! `solid_color_srgb` is a byte-faithful port of the retired artifact renderer's
4//! `solidColor`: FNV-1a over the name's UTF-16 code
5//! units, hue = ((hash >>> 8) % 360)/360, HSL(hue, 0.45, 0.6). Keeping the hash
6//! EXACT means re-baselined artifacts keep the colors users already know.
7
8/// FNV-1a over UTF-16 code units with wrapping 32-bit multiplies — byte-compatible
9/// with the original implementation.
10fn fnv1a_utf16(name: &str) -> u32 {
11    let mut hash: u32 = 2166136261;
12    for unit in name.encode_utf16() {
13        hash ^= unit as u32;
14        hash = hash.wrapping_mul(16777619);
15    }
16    hash
17}
18
19/// HSL → sRGB, the exact formula the retired soft raster used.
20fn hsl_to_rgb(h: f64, s: f64, l: f64) -> [f64; 3] {
21    let q = if l < 0.5 { l * (1.0 + s) } else { l + s - l * s };
22    let p = 2.0 * l - q;
23    let channel = |t: f64| -> f64 {
24        let t = t.rem_euclid(1.0);
25        if t < 1.0 / 6.0 {
26            p + (q - p) * 6.0 * t
27        } else if t < 0.5 {
28            q
29        } else if t < 2.0 / 3.0 {
30            p + (q - p) * (2.0 / 3.0 - t) * 6.0
31        } else {
32            p
33        }
34    };
35    [channel(h + 1.0 / 3.0), channel(h), channel(h - 1.0 / 3.0)]
36}
37
38/// The stable per-solid display color, in sRGB (0..1 per channel).
39pub fn solid_color_srgb(name: &str) -> [f64; 3] {
40    let hue = ((fnv1a_utf16(name) >> 8) % 360) as f64 / 360.0;
41    hsl_to_rgb(hue, 0.45, 0.6)
42}
43
44/// sRGB electro-optical transfer (decode): sRGB component → linear.
45pub fn srgb_to_linear(c: f64) -> f64 {
46    if c <= 0.04045 {
47        c / 12.92
48    } else {
49        ((c + 0.055) / 1.055).powf(2.4)
50    }
51}
52
53/// A 0xRRGGBB hex color → linear-space RGB (for light/material constants).
54pub fn hex_to_linear(hex: u32) -> [f32; 3] {
55    hex_to_srgb(hex).map(|channel| srgb_to_linear(channel) as f32)
56}
57
58/// A 0xRRGGBB hex color → sRGB-space RGB in 0..1 (for clear colors written to
59/// a non-sRGB target, where the bytes should equal the hex exactly).
60pub fn hex_to_srgb(hex: u32) -> [f64; 3] {
61    [
62        ((hex >> 16) & 0xff) as f64 / 255.0,
63        ((hex >> 8) & 0xff) as f64 / 255.0,
64        (hex & 0xff) as f64 / 255.0,
65    ]
66}
67
68/// A packed RGB color normalized for single-precision overlay and material buffers.
69pub(crate) fn hex_to_srgb_f32(hex: u32) -> [f32; 3] {
70    hex_to_srgb(hex).map(|channel| channel as f32)
71}
72
73// BREP private tests: 295e6514adee4780
brep_render/color.rs

brep_render/
color.rs
