brightnessFor static method

Brightness? brightnessFor(Color? color)

Determines whether the given Color is Brightness.light or Brightness.dark.

This compares the luminosity and opacity of the given color to a threshold value that matches the material design specification.

Implementation

static Brightness? brightnessFor(Color? color) {
  if (color == null) return null;

  // See <https://www.w3.org/TR/WCAG20/#contrast-ratiodef>
  // The spec says to use kThreshold=0.0525, but Material Design appears to bias
  // more towards using light text than WCAG20 recommends. Material Design spec
  // doesn't say what value to use, but 0.15 seemed close to what the Material
  // Design spec shows for its color palette on
  // <https://material.io/go/design-theming#color-color-palette>.
  const kLuminanceThreshold = 0.15;
  const kOpaqueThreshold = 0.6;

  final relativeLuminance = color.computeLuminance();
  final luminance = (relativeLuminance + 0.05) * (relativeLuminance + 0.05);
  final isLight = luminance > kLuminanceThreshold;
  final isOpaque = color.opacity > kOpaqueThreshold;

  return isLight
      ? isOpaque
          ? Brightness.light
          : Brightness.dark
      : isOpaque
          ? Brightness.dark
          : Brightness.light;
}