calculate method

@override void calculate(int index, ScrollProgressInfo info)

Implementation

@override
void calculate(int index, ScrollProgressInfo info) {
  double changeValue = info.progress;
  int alphaValueOffset = highlightColor.alpha - normalColor.alpha;
  int blueValueOffset = highlightColor.blue - normalColor.blue;
  int greenValueOffset = highlightColor.green - normalColor.green;
  int redValueOffset = highlightColor.red - normalColor.red;

  if (info.currentIndex == index) {
    transformColor = highlightColor
        .withAlpha(
            highlightColor.alpha - (alphaValueOffset * changeValue).toInt())
        .withBlue(
            highlightColor.blue - (blueValueOffset * changeValue).toInt())
        .withGreen(
            highlightColor.green - (greenValueOffset * changeValue).toInt())
        .withRed(highlightColor.red - (redValueOffset * changeValue).toInt());
  } else if (info.targetIndex == index) {
    transformColor = normalColor
        .withAlpha(
            normalColor.alpha + (alphaValueOffset * changeValue).toInt())
        .withBlue(normalColor.blue + (blueValueOffset * changeValue).toInt())
        .withGreen(
            normalColor.green + (greenValueOffset * changeValue).toInt())
        .withRed(normalColor.red + (redValueOffset * changeValue).toInt());
  } else {
    transformColor = normalColor;
    return;
  }
}