fluro/example/lib/helpers/color_helpers.dart

/*
 * router
 * A Posse Production
 * http://goposse.com
 * Copyright (c) 2017 Posse Productions LLC. All rights reserved.
 * See LICENSE for distribution and usage details.
 */
import 'package:flutter/material.dart';

enum ContrastPreference {
  none,
  light,
  dark,
}

class ColorHelpers {

  static int fromHexString(String argbHexString) {
    String useString = argbHexString;
    if (useString.startsWith("#")) {
      useString = useString.substring(1); // trim the starting '#'
    }
    if (useString.length < 8) {
      useString = "FF" + useString;
    }
    if (!useString.startsWith("0x")) {
      useString = "0x" + useString;
    }
    return int.parse(useString);
  }

  static final double _kMinContrastModifierRange = 0.35;
  static final double _kMaxContrastModifierRange = 0.65;

  /// Returns black or white depending on whether the source color is darker
  /// or lighter. If darker, will return white. If lighter, will return
  /// black. If the color is within 35-65% of the spectrum and a prefer
  /// value is specified, then white or black will be preferred.
  static Color blackOrWhiteContrastColor(Color sourceColor, {ContrastPreference prefer = ContrastPreference.none}) {
    // Will return a value between 0.0 (black) and 1.0 (white)
    double value = (((sourceColor.red * 299.0) + (sourceColor.green * 587.0) +
        (sourceColor.blue * 114.0)) / 1000.0) / 255.0;
    if (prefer != ContrastPreference.none) {
      if (value >= _kMinContrastModifierRange && value <= _kMaxContrastModifierRange) {
        return prefer == ContrastPreference.light ? new Color(0xFFFFFFFF) : new Color(0xFF000000);
      }
    }
    return value > 0.6 ? new Color(0xFF000000) : new Color(0xFFFFFFFF);
  }

}