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

using Microsoft.Xna.Framework;
using MrGameEng.Graphics;
using Xunit;

namespace MrGameEng.Graphics.Tests;

public class CullingTests
{
    [Fact]
    public void BoundingCircle_UnrotatedTopLeftOrigin_CenterIsRegionCenter()
    {
        var transform = Transform2D.At(new Vector2(100f, 200f));

        var (center, radius) = CullingMath.SpriteBoundingCircle(transform, 32f, 32f, Vector2.Zero);

        Assert.Equal(new Vector2(116f, 216f), center);
        Assert.Equal(0.5f * MathF.Sqrt(32f * 32f * 2f), radius, 3);
    }

    [Fact]
    public void BoundingCircle_CenterOrigin_CenterIsPosition()
    {
        var transform = Transform2D.At(new Vector2(50f, 50f));

        var (center, _) = CullingMath.SpriteBoundingCircle(
            transform,
            64f,
            32f,
            new Vector2(32f, 16f)
        );

        Assert.Equal(new Vector2(50f, 50f), center);
    }

    [Fact]
    public void BoundingCircle_Scale_GrowsRadius()
    {
        var transform = new Transform2D(Vector2.Zero, scale: new Vector2(2f, 2f));

        var (_, radius) = CullingMath.SpriteBoundingCircle(transform, 10f, 10f, Vector2.Zero);

        Assert.Equal(0.5f * MathF.Sqrt(800f), radius, 3);
    }

    [Fact]
    public void BoundingCircle_RegionOverload_MatchesSizeOverload_ForUniformScale()
    {
        var region = new Texture2DRegion(null!, new Rectangle(0, 0, 48, 24));
        var transform = new Transform2D(
            new Vector2(10f, 20f),
            rotation: 0.6f,
            scale: new Vector2(1.5f, 1.5f)
        );
        var origin = new Vector2(5f, 7f);

        var (centerA, radiusA) = CullingMath.SpriteBoundingCircle(transform, 48f, 24f, origin);
        var (centerB, radiusB) = CullingMath.SpriteBoundingCircle(in transform, region, origin);

        Assert.Equal(centerA.X, centerB.X, 3);
        Assert.Equal(centerA.Y, centerB.Y, 3);
        Assert.Equal(radiusA, radiusB, 3);
    }

    [Fact]
    public void BoundingCircle_RegionOverload_IsConservative_ForNonUniformScale()
    {
        var region = new Texture2DRegion(null!, new Rectangle(0, 0, 100, 10));
        var transform = new Transform2D(Vector2.Zero, scale: new Vector2(1f, 3f));

        var (_, exact) = CullingMath.SpriteBoundingCircle(transform, 100f, 10f, Vector2.Zero);
        var (_, conservative) = CullingMath.SpriteBoundingCircle(
            in transform,
            region,
            Vector2.Zero
        );

        Assert.True(conservative >= exact);
    }

    [Theory]
    [InlineData(50f, 50f, true)] // inside
    [InlineData(-4f, 50f, true)] // touching from the left (radius 5)
    [InlineData(-20f, 50f, false)] // far left
    [InlineData(50f, 130f, false)] // far below
    public void CircleIntersectsRect_DetectsOverlap(float x, float y, bool expected)
    {
        var rect = new RectF(0f, 0f, 100f, 100f);

        Assert.Equal(expected, CullingMath.CircleIntersectsRect(new Vector2(x, y), 5f, rect));
    }
}