hitTestSector function

int? hitTestSector({ required Size size, required RouletteGroup group, required double rotation, required Offset localPosition, double centerStickerPercent = 0, })

Determines which sector of a roulette the given localPosition falls in.

size is the widget size (assumed square). group is the RouletteGroup whose weighted sectors to test against. rotation is the current rotation angle in radians applied to the wheel. centerStickerPercent is the radius fraction of the center sticker (taps inside this circle return null).

Returns the 0-based sector index, or null if the tap is outside the wheel circle or inside the center sticker.

Implementation

int? hitTestSector({
  required Size size,
  required RouletteGroup group,
  required double rotation,
  required Offset localPosition,
  double centerStickerPercent = 0,
}) {
  final radius = size.width / 2;
  final center = Offset(size.width / 2, size.height / 2);
  final delta = localPosition - center;
  final distance = delta.distance;

  // Outside the circle.
  if (distance > radius) return null;

  // Inside the center sticker exclusion zone.
  if (centerStickerPercent > 0 && distance < radius * centerStickerPercent) {
    return null;
  }

  // The painter draws starting at angle -π/2 + rotation, so we reverse that
  // to obtain the angle in "sector space".
  final rawAngle = atan2(delta.dy, delta.dx);
  // Subtract the base rotation (-π/2 + rotation) to get the sector-local angle.
  var angle = rawAngle - (-pi / 2 + rotation);
  // Normalize to [0, 2π).
  angle = angle % (2 * pi);
  if (angle < 0) angle += 2 * pi;

  // Walk through sectors and find which one the angle falls in.
  double cumulative = 0;
  for (var i = 0; i < group.divide; i++) {
    final sweep = 2 * pi * group.units[i].weight / group.totalWeights;
    cumulative += sweep;
    if (angle < cumulative) return i;
  }
  // Floating-point edge case – attribute to last sector.
  return group.divide - 1;
}