mrgameeng/tests/MrGameEng.Atlases.Tests/ShelfPackerTests.cs

using MrGameEng.Atlases;
using Xunit;

namespace MrGameEng.Atlases.Tests;

public class ShelfPackerTests
{
    private static List<PackItem> Squares(int count, int size) =>
        Enumerable.Range(0, count).Select(i => new PackItem($"item{i:D3}", size, size)).ToList();

    [Fact]
    public void Pack_PlacesEveryItem_WithinPageBounds()
    {
        var result = ShelfPacker.Pack(Squares(50, 60), maxPageSize: 256, padding: 2);

        Assert.Equal(50, result.Placements.Count);
        foreach (var p in result.Placements)
        {
            var (pageWidth, pageHeight) = result.PageSizes[p.Page];
            Assert.True(p.X >= 2 && p.Y >= 2);
            Assert.True(p.X + p.Width <= pageWidth);
            Assert.True(p.Y + p.Height <= pageHeight);
        }
    }

    [Fact]
    public void Pack_NoTwoPlacements_Overlap()
    {
        var items = new List<PackItem>();
        var random = new Random(42);
        for (var i = 0; i < 200; i++)
        {
            items.Add(new PackItem($"r{i:D3}", random.Next(4, 90), random.Next(4, 90)));
        }

        var result = ShelfPacker.Pack(items, maxPageSize: 512, padding: 2);

        var byPage = result.Placements.GroupBy(p => p.Page);
        foreach (var page in byPage)
        {
            var list = page.ToList();
            for (var i = 0; i < list.Count; i++)
            {
                for (var j = i + 1; j < list.Count; j++)
                {
                    var a = list[i];
                    var b = list[j];
                    var separated =
                        a.X + a.Width + 2 <= b.X || b.X + b.Width + 2 <= a.X ||
                        a.Y + a.Height + 2 <= b.Y || b.Y + b.Height + 2 <= a.Y;
                    Assert.True(separated, $"{a.Key} overlaps {b.Key} (padding included)");
                }
            }
        }
    }

    [Fact]
    public void Pack_Overflows_ToMultiplePages()
    {
        // 9 квадратов 100² на страницу 256² помещаются максимум по 4.
        var result = ShelfPacker.Pack(Squares(9, 100), maxPageSize: 256, padding: 2);

        Assert.True(result.PageSizes.Count >= 3);
        Assert.Equal(Enumerable.Range(0, result.PageSizes.Count), result.Placements.Select(p => p.Page).Distinct().Order());
    }

    [Fact]
    public void Pack_OversizedItem_GetsDedicatedPage()
    {
        var items = Squares(2, 30);
        items.Add(new PackItem("huge", 500, 40));

        var result = ShelfPacker.Pack(items, maxPageSize: 256, padding: 2);

        var huge = result.Placements.Single(p => p.Key == "huge");
        Assert.Single(result.Placements, p => p.Page == huge.Page);
        Assert.True(result.PageSizes[huge.Page].Width >= 504);
    }

    [Fact]
    public void Pack_IsDeterministic_RegardlessOfInputOrder()
    {
        var items = Squares(30, 20).Concat(Squares(10, 50).Select(i => i with { Key = "b" + i.Key })).ToList();
        var shuffled = items.AsEnumerable().Reverse().ToList();

        var a = ShelfPacker.Pack(items, 128, 2);
        var b = ShelfPacker.Pack(shuffled, 128, 2);

        Assert.Equal(
            a.Placements.OrderBy(p => p.Key, StringComparer.Ordinal),
            b.Placements.OrderBy(p => p.Key, StringComparer.Ordinal));
    }

    [Fact]
    public void Pack_TrimsPages_ToPowerOfTwo()
    {
        var result = ShelfPacker.Pack(Squares(1, 50), maxPageSize: 2048, padding: 2);

        Assert.Equal((64, 64), result.PageSizes.Single());
    }

    [Theory]
    [InlineData(1, 1)]
    [InlineData(64, 64)]
    [InlineData(65, 128)]
    [InlineData(2048, 2048)]
    public void NextPowerOfTwo_RoundsUp(int value, int expected)
    {
        Assert.Equal(expected, ShelfPacker.NextPowerOfTwo(value));
    }

    [Fact]
    public void Pack_NonPowerOfTwoLimit_SharedPagesNeverExceedIt()
    {
        // 40² с padding на лимит 100: POT-округление дало бы 128 > лимита.
        var result = ShelfPacker.Pack(Squares(10, 40), maxPageSize: 100, padding: 2);

        Assert.All(result.PageSizes, size =>
        {
            Assert.True(size.Width <= 100, $"page width {size.Width} > 100");
            Assert.True(size.Height <= 100, $"page height {size.Height} > 100");
        });
    }

    [Fact]
    public void Pack_OversizedItem_PageHasExactPaddedSize()
    {
        var result = ShelfPacker.Pack([new PackItem("big", 300, 50)], maxPageSize: 128, padding: 2);

        Assert.Equal((304, 54), result.PageSizes.Single());
    }

    [Fact]
    public void Pack_OversizedAmongSmall_DoesNotSplitSharedPage()
    {
        // Широкий и низкий негабарит сортируется в конец по высоте; раньше он закрывал
        // наполовину заполненную общую страницу, и остаток уезжал на новую.
        var items = new List<PackItem> { new("big", 300, 10) };
        for (var i = 0; i < 4; i++)
        {
            items.Add(new PackItem($"s{i}", 30, 30));
        }

        var result = ShelfPacker.Pack(items, maxPageSize: 128, padding: 2);

        Assert.Equal(2, result.PageSizes.Count); // отдельная страница big + одна общая
    }
}