colorBlindnessAssertContrast function

void colorBlindnessAssertContrast(ColorScheme scheme, [ double minThreshold = 4.5 ])

This method simulates color blindness in a ColorScheme and compares primary, secondary against background, surface.

Should be used in CI and tests.

Input: ColorScheme: the ColorScheme you are using as your theme. double: the minimum threshold in WCAG 2.1 where it should pass. The value is usually 4.5 (AA) or 7.0 (AAA). Contrast ranges from 0 to 21.

Output: if successful: nothing if there is an error: it will throw an exception

Implementation

void colorBlindnessAssertContrast(ColorScheme scheme,
    [double minThreshold = 4.5]) {
  for (ColorBlindnessType type in ColorBlindnessType.values) {
    final updatedScheme = colorBlindnessColorScheme(scheme, type);

    void calculate({
      required Color aColor,
      required Color bColor,
      required String aStr,
      required String bStr,
    }) {
      final contrast = _calculateContrast(aColor, bColor);
      if (contrast < minThreshold) {
        throw Exception(
            "Fail! For ${type.toString().substring(19)}, $aStr ($aColor) on $bStr ($bColor) got value ${contrast.toStringAsFixed(2)}");
      }
    }

    calculate(
      aColor: updatedScheme.primary,
      bColor: updatedScheme.background,
      aStr: "primary",
      bStr: "background",
    );

    calculate(
      aColor: updatedScheme.primary,
      bColor: updatedScheme.surface,
      aStr: "primary",
      bStr: "surface",
    );

    calculate(
      aColor: updatedScheme.secondary,
      bColor: updatedScheme.background,
      aStr: "secondary",
      bStr: "background",
    );

    calculate(
      aColor: updatedScheme.secondary,
      bColor: updatedScheme.background,
      aStr: "secondary",
      bStr: "surface",
    );
  }
}