Module contrast 

WCAG 2.1 contrast primitives. Cases 1, 4, and 5 all measure against these — implement once, correctly.

relative_luminance works on linearized sRGB; the conversion lives in color::linear_srgb_of so this file does not duplicate the gamma curve.

Constants

AA_LARGE_TEXT

AA threshold for large text (>= 18pt regular / 14pt bold).

AA_NON_TEXT

AA threshold for UI components, icons, borders.

AA_TEXT

AA threshold for normal-sized text.

DARK_BG

Page background for the future dark mode (§8 — emitted today even though the framework is light-only).

LIGHT_BG

Page background the engine measures the light-mode palette against.

TEXT_ON_DARK

Default near-white text used on dark surfaces.

TEXT_ON_LIGHT

Default near-black text used on light surfaces.

Functions

contrast_ratio

WCAG 2.1 contrast ratio. Range 1.0..=21.0 — identical colors give 1.0, black-on-white gives 21.0.

relative_luminance

WCAG 2.1 relative luminance of an sRGB color, range 0.0..=1.0.