feat(design): 配色来源纯数学层（Monet 式量化取色 + 色卡 + 三级回落 + 对比度收敛）
D40 分层：design 保持零第三方依赖，只吃已解码的 RGBA 像素。 - palette/quantize：5bit 直方图 + CIELAB k-means（QuantizerCelebi/Score 的形状） - palette/score：官方 Score 口径（CUTOFF_CHROMA 5 / TARGET 48 / 权重 0.7+0.3） - palette/seed：seed_from_rgba + D40 彩度门槛 8，灰白图回落而非凭空上色 - palette/card：8 张内置色卡，key 为持久化键 - palette/wcag：26 对文字对比度门禁 + 沿 tone 轴收敛并记录修正 - palette/resolve：纯函数三级来源编排 + Provenance（原因码/提示键）
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//! 对比度校验与**收敛**：任意一套方案（不管种子来自图片还是色卡）都要过同一道门。
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//!
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//! 为什么需要这一层：`tests/contrast_aa.rs` 的 208 项门禁只覆盖**候选色卡**（它拿 6 个手挑的
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//! 种子逐对断言）。D38/D40 之后「方案生成」还可能吃图片来的种子，而远程证据不能只靠
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//! 「tone 轴固定所以一定达标」这句话——那条性质对本 crate 的生成器成立，但一旦有人手动改角色、
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//! 或者将来接别的生成器（比如非 TonalSpot 变体），门禁必须当场发现。所以：
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//!
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//! 1. [`check`] 对**任何** [`Scheme`] 跑全表（26 对文字/图标对，AA ≥ 4.5:1）；
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//! 2. [`converge`] 不达标就**沿 tone 轴修正前景色**（保住色相，只动明度），并把每一处修正
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//! 连同「改前/改后的实测对比度」记进 [`Adjustment`]，让 UI 能说「为了可读性微调了强调色」；
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//! 3. 修正后仍然不达标的方案，由 [`super::resolve`] 回落到色卡并在 `Provenance` 里登记原因。
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//!
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//! ## 为什么只改前景、不改背景
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//!
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//! 背景（`surface` / `*-container`）决定整个界面的骨架与层级，改它会让「同一套方案的两个页面
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//! 底色不一样」；前景（`on-*`）本来就是为可读性服务的，动它代价最小。方向也不是猜的：
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//! 背景 tone ≥ 50（浅底）就压暗前景，否则提亮前景——修正方向永远朝着「离背景更远」的那一侧。
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//!
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//! ## 只做 4.5:1 这一档，`outline` 不在门禁里
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//!
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//! M3 里 `outline` 是非文字元素（输入框描边），规范目标是 3:1，且它按设计就贴着 surface；
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//! `outline-variant` 是纯装饰分隔线。这两个的例外登记在 `crates/design/src/color/mod.rs` 的
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//! 「对比度纪律」小节，本模块不重复断言（重复断言只会让两边口径打架）。
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use crate::color::{Color, Hct, Role, Scheme};
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/// 正文/图标对的 AA 门槛（WCAG 2.x：普通文字 4.5:1）。
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pub const AA_TEXT: f32 = 4.5;
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/// 非文字元素的门槛（描边/图标块 3:1）——本模块不自动收敛这一档，只提供常量给调用方参考。
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pub const AA_NON_TEXT: f32 = 3.0;
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/// 文字/图标对（前景, 承载色）。与 `tests/contrast_aa.rs` 的 `TEXT_PAIRS` 同表。
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pub const TEXT_PAIRS: [(Role, Role); 26] = [
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(Role::OnPrimary, Role::Primary),
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(Role::OnPrimaryContainer, Role::PrimaryContainer),
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(Role::OnSecondary, Role::Secondary),
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(Role::OnSecondaryContainer, Role::SecondaryContainer),
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(Role::OnTertiary, Role::Tertiary),
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(Role::OnTertiaryContainer, Role::TertiaryContainer),
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(Role::OnError, Role::Error),
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(Role::OnErrorContainer, Role::ErrorContainer),
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(Role::OnSurface, Role::Surface),
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(Role::OnSurfaceVariant, Role::SurfaceVariant),
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(Role::OnBackground, Role::Background),
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(Role::InverseOnSurface, Role::InverseSurface),
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(Role::InversePrimary, Role::InverseSurface),
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(Role::OnPrimaryFixed, Role::PrimaryFixed),
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(Role::OnPrimaryFixedVariant, Role::PrimaryFixedDim),
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(Role::OnSecondaryFixed, Role::SecondaryFixed),
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(Role::OnSecondaryFixedVariant, Role::SecondaryFixedDim),
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(Role::OnTertiaryFixed, Role::TertiaryFixed),
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(Role::OnTertiaryFixedVariant, Role::TertiaryFixedDim),
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(Role::OnSurface, Role::SurfaceContainerLowest),
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(Role::OnSurface, Role::SurfaceContainerLow),
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(Role::OnSurface, Role::SurfaceContainer),
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(Role::OnSurface, Role::SurfaceContainerHigh),
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(Role::OnSurface, Role::SurfaceContainerHighest),
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(Role::OnSurfaceVariant, Role::SurfaceContainerHighest),
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(Role::OnSurfaceVariant, Role::SurfaceContainerLow),
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];
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/// 一处不达标。
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#[derive(Debug, Clone, Copy, PartialEq)]
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pub struct Failure {
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/// 前景角色。
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pub fg: Role,
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/// 承载色角色。
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pub bg: Role,
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/// 实测对比度。
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pub ratio: f32,
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/// 要求的下限（目前恒为 [`AA_TEXT`]）。
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pub required: f32,
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}
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/// 一套方案的对比度体检结果。
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#[derive(Debug, Clone, PartialEq)]
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pub struct WcagReport {
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/// 全部不达标项（空 = 通过）。
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pub failures: Vec<Failure>,
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/// 全表里最低的对比度（用来观察「刚好卡线」的方案）。
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pub worst: f32,
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}
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impl WcagReport {
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/// 是否全部达标。
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pub fn is_clean(&self) -> bool {
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self.failures.is_empty()
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}
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}
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/// 对任意方案跑全表断言。
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pub fn check(scheme: &Scheme) -> WcagReport {
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let mut failures = Vec::new();
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let mut worst = f32::INFINITY;
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for (fg, bg) in TEXT_PAIRS {
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let ratio = scheme.contrast(fg, bg);
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worst = worst.min(ratio);
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if ratio < AA_TEXT {
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failures.push(Failure {
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fg,
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bg,
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ratio,
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required: AA_TEXT,
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});
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}
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}
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WcagReport { failures, worst }
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}
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/// 一处自动修正的记录（UI 可以拿去写「为可读性微调了强调色」）。
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#[derive(Debug, Clone, Copy, PartialEq)]
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pub struct Adjustment {
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/// 被改的角色。
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pub role: Role,
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/// 为了跟谁达标而改的（承载色角色）。
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pub against: Role,
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/// 改前的色值。
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pub before: Color,
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/// 改后的色值。
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pub after: Color,
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/// 改前的对比度。
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pub before_ratio: f32,
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/// 改后的对比度。
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pub after_ratio: f32,
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}
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/// 不达标就沿 tone 轴修正，返回（修正后的方案, 修正记录）。
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///
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/// 最多三遍：一遍修正后可能让「同一个前景对另一个承载色」变得不达标（例如 `on-surface`
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/// 同时压在 6 个 surface-container 上），多遍保证收敛。修不动的情况（理论上不存在：纯黑/纯白
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/// 对任意背景都 ≥ 4.58:1）会保留原值，由调用方用 [`check`] 复核后决定是否回落。
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pub fn converge(scheme: Scheme) -> (Scheme, Vec<Adjustment>) {
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let mut colors = [Color::BLACK; 49];
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for (role, color) in scheme.iter() {
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colors[role as usize] = color;
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}
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let mut adjustments = Vec::new();
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for _ in 0..3 {
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let mut changed = false;
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for (fg, bg) in TEXT_PAIRS {
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let before = colors[fg as usize];
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let background = colors[bg as usize];
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let before_ratio = before.contrast_ratio(background);
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if before_ratio >= AA_TEXT {
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continue;
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}
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let Some(after) = shift_away_from(before, background, AA_TEXT) else {
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continue;
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};
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colors[fg as usize] = after;
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adjustments.push(Adjustment {
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role: fg,
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against: bg,
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before,
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after,
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before_ratio,
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after_ratio: after.contrast_ratio(background),
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});
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changed = true;
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}
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if !changed {
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break;
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}
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}
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(Scheme::from_colors(scheme.flavor(), colors), adjustments)
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}
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/// 保住色相、压掉彩度地往「离背景更远」的 tone 走，直到达标或到尽头。
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fn shift_away_from(foreground: Color, background: Color, min_ratio: f32) -> Option<Color> {
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let hct = Hct::from_color(foreground);
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let darken = background.lstar() >= 50.0;
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let step = if darken { -4.0 } else { 4.0 };
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let mut tone = hct.tone.round();
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for _ in 0..=25 {
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tone += step;
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if !(0.0..=100.0).contains(&tone) {
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break;
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}
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// 修正是「为了可读性」而不是「换个品牌色」：色相不动，彩度让求解器自己压到色域内。
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let candidate = Hct::from_components(hct.hue, hct.chroma, tone).to_color();
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if candidate.contrast_ratio(background) >= min_ratio {
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return Some(candidate);
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}
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}
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// 尽头兜底：纯黑/纯白对任何背景都在 4.58:1 以上（中灰处的理论最低点）。
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let extreme = if darken { Color::BLACK } else { Color::WHITE };
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(extreme.contrast_ratio(background) >= min_ratio).then_some(extreme)
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use crate::color::SchemeFlavor;
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#[test]
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fn baseline_is_clean() {
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for flavor in [SchemeFlavor::Light, SchemeFlavor::Dark] {
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let report = check(&Scheme::baseline(flavor));
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assert!(report.is_clean(), "{flavor:?}: {:?}", report.failures);
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assert!(report.worst >= AA_TEXT, "{flavor:?} worst {}", report.worst);
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}
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}
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#[test]
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fn hostile_scheme_is_detected() {
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// 反证：把 on-surface 换成 surface（对比度 1:1），校验器必须报出来。
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let base = Scheme::baseline(SchemeFlavor::Light);
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let mut colors = [Color::BLACK; 49];
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for (role, color) in base.iter() {
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colors[role as usize] = color;
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}
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colors[Role::OnSurface as usize] = base.get(Role::Surface);
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let hostile = Scheme::from_colors(SchemeFlavor::Light, colors);
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let report = check(&hostile);
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assert!(!report.is_clean());
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assert!(report
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.failures
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.iter()
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.any(|failure| failure.fg == Role::OnSurface && failure.bg == Role::Surface));
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}
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#[test]
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fn converge_repairs_a_hostile_scheme() {
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let base = Scheme::baseline(SchemeFlavor::Light);
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let mut colors = [Color::BLACK; 49];
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for (role, color) in base.iter() {
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colors[role as usize] = color;
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}
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colors[Role::OnSurface as usize] = base.get(Role::Surface);
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colors[Role::OnPrimary as usize] = base.get(Role::Primary);
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let hostile = Scheme::from_colors(SchemeFlavor::Light, colors);
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let (fixed, adjustments) = converge(hostile);
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assert!(!adjustments.is_empty(), "应当记录了修正");
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assert!(check(&fixed).is_clean(), "{:?}", check(&fixed).failures);
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for adjustment in &adjustments {
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assert!(adjustment.after_ratio >= AA_TEXT);
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assert!(adjustment.after_ratio > adjustment.before_ratio);
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}
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}
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#[test]
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fn converge_is_a_no_op_on_a_healthy_scheme() {
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let clean = Scheme::baseline(SchemeFlavor::Dark);
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let (fixed, adjustments) = converge(clean);
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assert!(adjustments.is_empty());
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assert_eq!(fixed, clean);
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}
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#[test]
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fn shift_darkens_on_light_background_and_lightens_on_dark() {
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let light_bg = Scheme::baseline(SchemeFlavor::Light);
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let surface = light_bg.get(Role::Surface);
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let fixed = shift_away_from(surface, surface, 4.5).expect("浅底上前景可以压暗");
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assert!(
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fixed.lstar() < surface.lstar() - 20.0,
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"压暗后 tone = {}",
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fixed.lstar()
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);
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assert!(fixed.contrast_ratio(surface) >= 4.5);
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let dark_bg = Scheme::baseline(SchemeFlavor::Dark);
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let surface = dark_bg.get(Role::Surface);
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let fixed = shift_away_from(surface, surface, 4.5).expect("深底上前景可以提亮");
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assert!(
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fixed.lstar() > surface.lstar() + 20.0,
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"提亮后 tone = {}",
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fixed.lstar()
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);
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assert!(fixed.contrast_ratio(surface) >= 4.5);
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// 色相不跟着动：修正只动明度（改前改后的 CAM16 色相差 < 2°）。
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let before = Hct::from_color(surface);
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let after = Hct::from_color(fixed);
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let delta = (before.hue - after.hue)
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.abs()
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.min(360.0 - (before.hue - after.hue).abs());
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assert!(delta < 2.0, "色相被改了 {delta}°");
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}
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}
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