getAnimationTargetIndex function

int getAnimationTargetIndex({ required double dx, required double dy, required int total, required Size itemSize, required Offset offset, required Offset scroll, required double crossAxisSpacing, required double mainAxisSpacing, required Axis direction, required int crossCount, })

Computing Animation Target Index

Implementation

int getAnimationTargetIndex({
  required double dx,
  required double dy,
  required int total,
  required Size itemSize,
  required Offset offset,
  required Offset scroll,
  required double crossAxisSpacing,
  required double mainAxisSpacing,
  required Axis direction,
  required int crossCount,
}) {
  int topIndex = 0;
  int leftIndex = 0;
  int targetIndex = 0;

  double newTop = 0;
  double newLeft = 0;
  double newWidth = 0;
  double newHeight = 0;

  final tx = dx + scroll.dx;
  final ty = dy + scroll.dy;
  final left = tx - offset.dx - itemSize.width / 2 - 16.0;
  final top = ty - offset.dy - itemSize.height / 2 - 16.0;

  if (direction == Axis.vertical) {
    newTop = top + mainAxisSpacing / 2;
    newLeft = left + crossAxisSpacing / 2;
    newWidth = itemSize.width + crossAxisSpacing;
    newHeight = itemSize.height + mainAxisSpacing;

    topIndex = max((newTop / newHeight).round(), 0);
    leftIndex = max((newLeft / newWidth).round(), 0);
    targetIndex = leftIndex + crossCount * topIndex;
  }

  if (direction == Axis.horizontal) {
    newTop = top + crossAxisSpacing / 2;
    newLeft = left + mainAxisSpacing / 2;
    newWidth = itemSize.width + mainAxisSpacing;
    newHeight = itemSize.height + crossAxisSpacing;

    topIndex = max((newTop / newHeight).round(), 0);
    leftIndex = max((newLeft / newWidth).round(), 0);
    targetIndex = topIndex + crossCount * leftIndex;
  }

  if (targetIndex >= total) {
    targetIndex = total - 1;
  }

  if (targetIndex < 0) {
    targetIndex = 0;
  }

  return targetIndex;
}