zoomForScale static method

KLineZoomResult zoomForScale({ required double startBeginIndex, required double startItemCount, required double scale, required double startFocalDx, required double currentFocalDx, required double viewportWidth, required int dataLength, required double minItemCount, required double maxItemCount, })

Implementation

static KLineZoomResult zoomForScale({
  required double startBeginIndex,
  required double startItemCount,
  required double scale,
  required double startFocalDx,
  required double currentFocalDx,
  required double viewportWidth,
  required int dataLength,
  required double minItemCount,
  required double maxItemCount,
}) {
  if (dataLength <= 0 || startItemCount <= 0 || viewportWidth <= 0) {
    return const KLineZoomResult(beginIndex: 0.0, itemCount: 0.0);
  }

  final safeScale = scale > 0 ? scale : 1.0;
  final maxVisibleCount = min(maxItemCount, dataLength.toDouble());
  final minVisibleCount = min(minItemCount, maxVisibleCount);
  final nextItemCount = (startItemCount / safeScale)
      .clamp(minVisibleCount, maxVisibleCount)
      .toDouble();

  final startFocalRatio = (startFocalDx / viewportWidth).clamp(0.0, 1.0);
  final currentFocalRatio = (currentFocalDx / viewportWidth).clamp(0.0, 1.0);
  final focalDataIndex = startBeginIndex + startItemCount * startFocalRatio;
  final rawBeginIndex = focalDataIndex - nextItemCount * currentFocalRatio;
  final maxBeginIndex = max(0.0, dataLength - nextItemCount);

  return KLineZoomResult(
    beginIndex: rawBeginIndex.clamp(0.0, maxBeginIndex).toDouble(),
    itemCount: nextItemCount,
  );
}