scaleForCenter function

double scaleForCenter({ required double center, required double basePos, required double baseHalfDim, required double displayLow, required double displayHigh, required ScaleResponse? response, })

Per-axis scaleResponse: given the rect's center on the axis, returns the corresponding scale factor by reading the lerp between geometric endpoints. In-display zone end = "rect's near edge touches display edge, size = base * inDisplay.end"; past-display zone end = "rect's far edge touches display edge, size = base * pastDisplay.end".

Implementation

double scaleForCenter({
  required double center,
  required double basePos,
  required double baseHalfDim,
  required double displayLow,
  required double displayHigh,
  required ScaleResponse? response,
}) {
  if (response == null) return 1.0;
  final isHigh = center >= basePos;
  final dir = isHigh ? 1.0 : -1.0;
  final dispEdge = isHigh ? displayHigh : displayLow;
  final inEnd = response.inDisplay?.end ?? 1.0;
  final inEndCenter = dispEdge - dir * baseHalfDim * inEnd;
  final travel = (center - basePos) * dir;
  final inTravel = (inEndCenter - basePos) * dir;
  if (travel <= inTravel || response.pastDisplay == null) {
    final p = inTravel > 0 ? (travel / inTravel).clamp(0.0, 1.0) : 0.0;
    final curveP = response.inDisplay?.curve.transform(p) ?? 0.0;
    return 1.0 + (inEnd - 1.0) * curveP;
  }
  final pastEnd = response.pastDisplay!.end;
  final pastEndCenter = dispEdge + dir * baseHalfDim * pastEnd;
  final pastTravel = (pastEndCenter - inEndCenter) * dir;
  final p = pastTravel > 0 ? ((travel - inTravel) / pastTravel).clamp(0.0, 1.0) : 1.0;
  final curveP = response.pastDisplay!.curve.transform(p);
  return inEnd + (pastEnd - inEnd) * curveP;
}