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

using Microsoft.Xna.Framework;
using MrGameEng.Core;
using MrGameEng.Lighting;
using Xunit;

namespace MrGameEng.Lighting.Tests;

public class DayNightTests
{
    private static (GameClock Clock, DayNight DayNight) Make()
    {
        var clock = new GameClock();
        var calendar = new Calendar(clock, secondsPerDay: 24f); // 1 second = 1 in-game hour
        return (clock, new DayNight(calendar, DayNightSettings.Default));
    }

    [Fact]
    public void Daylight_ZeroAtMidnight_OneAtNoon()
    {
        var (clock, dayNight) = Make();

        Assert.Equal(0f, dayNight.Daylight, 3); // 00:00

        clock.Advance(12f); // 12:00
        Assert.Equal(1f, dayNight.Daylight, 3);
    }

    [Fact]
    public void Daylight_RisesFromDawnToNoon()
    {
        var (clock, dayNight) = Make();

        clock.Advance(6f); // 06:00
        var dawn = dayNight.Daylight;
        clock.Advance(3f); // 09:00
        var mid = dayNight.Daylight;
        clock.Advance(3f); // 12:00
        var noon = dayNight.Daylight;

        Assert.True(dawn < mid && mid < noon, "daylight should rise from dawn to noon");
    }

    [Fact]
    public void SunShadow_ZeroAtNight_PointsWestInMorning_EastInAfternoon_ShortAtNoon()
    {
        var (clock, dayNight) = Make(); // 1s = 1 in-game hour

        Assert.Equal(Vector2.Zero, dayNight.SunShadow(8f)); // 00:00 — night, no sun

        clock.Advance(7f); // 07:00 — low morning sun in the east
        var morning = dayNight.SunShadow(8f);
        Assert.True(morning.X < 0f, "morning shadow points west");
        Assert.True(morning.Length() > 2f, "low sun casts a long shadow");

        clock.Advance(5f); // 12:00 — sun overhead
        Assert.True(dayNight.SunShadow(8f).Length() < 1f, "noon sun casts almost no shadow");

        clock.Advance(5f); // 17:00 — afternoon sun in the west
        Assert.True(dayNight.SunShadow(8f).X > 0f, "afternoon shadow points east");
    }

    [Fact]
    public void Ambient_DarkerAtNightThanAtNoon()
    {
        var (clock, dayNight) = Make();

        var night = dayNight.Ambient; // 00:00
        clock.Advance(12f); // 12:00
        var noon = dayNight.Ambient;

        Assert.True(night.R < noon.R && night.G < noon.G && night.B < noon.B);
        Assert.Equal(255, noon.R); // day color is white at noon
    }
}