calculateScale function

double calculateScale(
  1. Offset center,
  2. Offset startPoint,
  3. Offset currentPoint
)

Implementation

double calculateScale(Offset center, Offset startPoint, Offset currentPoint) {
  // 计算缩放比例
  double initialDistance = (startPoint - center).distance;
  double currentDistance = (currentPoint- center).distance;
  return currentDistance / initialDistance;
}