public void Test_S2PaddedCell_ShrinkToFit()
{
const int kIters = 1000;
for (int iter = 0; iter < kIters; ++iter)
{
// Start with the desired result and work backwards.
S2CellId result = S2Testing.GetRandomCellId();
R2Rect result_uv = result.BoundUV();
R2Point size_uv = result_uv.GetSize();
// Find the biggest rectangle that fits in "result" after padding.
// (These calculations ignore numerical errors.)
double max_padding = 0.5 * Math.Min(size_uv[0], size_uv[1]);
double padding = max_padding * S2Testing.Random.RandDouble();
R2Rect max_rect = result_uv.Expanded(-padding);
// Start with a random subset of the maximum rectangle.
R2Point a = new(SampleInterval(max_rect[0]), SampleInterval(max_rect[1]));
R2Point b = new(SampleInterval(max_rect[0]), SampleInterval(max_rect[1]));
if (!result.IsLeaf())
{
// If the result is not a leaf cell, we must ensure that no child of
// "result" also satisfies the conditions of ShrinkToFit(). We do this
// by ensuring that "rect" intersects at least two children of "result"
// (after padding).
int axis = S2Testing.Random.Uniform(2);
double center = result.CenterUV()[axis];
// Find the range of coordinates that are shared between child cells
// along that axis.
R1Interval shared = new(center - padding, center + padding);
double mid = SampleInterval(shared.Intersection(max_rect[axis]));
a = a.SetAxis(axis, SampleInterval(new R1Interval(max_rect[axis].Lo, mid)));
b = b.SetAxis(axis, SampleInterval(new R1Interval(mid, max_rect[axis].Hi)));
}
R2Rect rect = R2Rect.FromPointPair(a, b);
// Choose an arbitrary ancestor as the S2PaddedCell.
S2CellId initial_id = result.Parent(S2Testing.Random.Uniform(result.Level() + 1));
Assert.Equal(result, new S2PaddedCell(initial_id, padding).ShrinkToFit(rect));
}
}