mrgameeng/tests/MrGameEng.Graphics.Tests/SpriteBatcherTests.cs

using MrGameEng.Graphics;
using Xunit;

namespace MrGameEng.Graphics.Tests;

public class SpriteBatcherTests
{
    private static SpriteInstance Instance(byte layer) => new() { Layer = layer };

    [Fact]
    public void Sort_OrdersByKey_ReturningOriginalIndices()
    {
        var batcher = new SpriteBatcher(initialCapacity: 2);

        batcher.Submit(Instance(2), SpriteSortKey.Make(2, 0f, 0));
        batcher.Submit(Instance(0), SpriteSortKey.Make(0, 0f, 0));
        batcher.Submit(Instance(1), SpriteSortKey.Make(1, 0f, 0));

        var order = batcher.Sort();

        Assert.Equal(3, order.Length);
        Assert.Equal(0, batcher[order[0]].Layer);
        Assert.Equal(1, batcher[order[1]].Layer);
        Assert.Equal(2, batcher[order[2]].Layer);
    }

    [Fact]
    public void Submit_GrowsBeyondInitialCapacity()
    {
        var batcher = new SpriteBatcher(initialCapacity: 1);

        for (var i = 0; i < 100; i++)
        {
            batcher.Submit(Instance(0), (ulong)(100 - i));
        }

        Assert.Equal(100, batcher.Count);
        var order = batcher.Sort();
        Assert.Equal(99, order[0]); // последний сабмит имеет наименьший ключ
    }

    [Fact]
    public void Sort_IsStable_EqualKeysKeepSubmissionOrder()
    {
        var batcher = new SpriteBatcher();
        var key = SpriteSortKey.Make(1, 5f, 7);

        for (byte i = 0; i < 50; i++)
        {
            batcher.Submit(Instance(i), key); // одинаковый ключ у всех
        }

        var order = batcher.Sort();

        for (var i = 0; i < 50; i++)
        {
            Assert.Equal(i, order[i]);
        }
    }

    [Fact]
    public void Sort_IsStable_WithinMixedKeys()
    {
        var batcher = new SpriteBatcher();
        var keyA = SpriteSortKey.Make(0, 0f, 1);
        var keyB = SpriteSortKey.Make(2, 3f, 9);

        // Чередуем два ключа: внутри каждой группы порядок сабмита должен сохраниться.
        for (byte i = 0; i < 20; i++)
        {
            batcher.Submit(Instance(i), i % 2 == 0 ? keyA : keyB);
        }

        var order = batcher.Sort();

        var expectedA = new[] { 0, 2, 4, 6, 8, 10, 12, 14, 16, 18 };
        var expectedB = new[] { 1, 3, 5, 7, 9, 11, 13, 15, 17, 19 };
        Assert.Equal(expectedA, order[..10].ToArray());
        Assert.Equal(expectedB, order[10..].ToArray());
    }

    [Fact]
    public void Sort_LargeRandomSet_FullyOrdered()
    {
        var batcher = new SpriteBatcher(initialCapacity: 16);
        var random = new Random(123);
        var keys = new ulong[5000];
        for (var i = 0; i < keys.Length; i++)
        {
            keys[i] = (ulong)random.NextInt64();
            batcher.Submit(Instance(0), keys[i]);
        }

        var order = batcher.Sort();

        for (var i = 1; i < order.Length; i++)
        {
            Assert.True(keys[order[i - 1]] <= keys[order[i]]);
        }
    }

    [Fact]
    public void Clear_ResetsCount_KeepsWorking()
    {
        var batcher = new SpriteBatcher();
        batcher.Submit(Instance(0), 5);
        batcher.Clear();

        Assert.Equal(0, batcher.Count);
        batcher.Submit(Instance(1), 1);
        Assert.Equal(1, batcher.Count);
        Assert.Equal(1, batcher[batcher.Sort()[0]].Layer);
    }
}