tbd-station-14/Content.Shared/Light/EntitySystems/SharedLightCycleSystem.cs

using Content.Shared.Light.Components;
using Robust.Shared.Map.Components;

namespace Content.Shared.Light.EntitySystems;

public abstract class SharedLightCycleSystem : EntitySystem
{
    public override void Initialize()
    {
        base.Initialize();
        SubscribeLocalEvent<LightCycleComponent, MapInitEvent>(OnCycleMapInit);
        SubscribeLocalEvent<LightCycleComponent, ComponentShutdown>(OnCycleShutdown);
    }

    protected virtual void OnCycleMapInit(Entity<LightCycleComponent> ent, ref MapInitEvent args)
    {
        if (TryComp(ent.Owner, out MapLightComponent? mapLight))
        {
            ent.Comp.OriginalColor = mapLight.AmbientLightColor;
            Dirty(ent);
        }
    }

    private void OnCycleShutdown(Entity<LightCycleComponent> ent, ref ComponentShutdown args)
    {
        if (TryComp(ent.Owner, out MapLightComponent? mapLight))
        {
            mapLight.AmbientLightColor = ent.Comp.OriginalColor;
            Dirty(ent.Owner, mapLight);
        }
    }

    public void SetOffset(Entity<LightCycleComponent> entity, TimeSpan offset)
    {
        entity.Comp.Offset = offset;
        var ev = new LightCycleOffsetEvent(offset);

        RaiseLocalEvent(entity, ref ev);
        Dirty(entity);
    }

    public static Color GetColor(Entity<LightCycleComponent> cycle, Color color, float time)
    {
        if (cycle.Comp.Enabled)
        {
            var lightLevel = CalculateLightLevel(cycle.Comp, time);
            var colorLevel = CalculateColorLevel(cycle.Comp, time);
            return new Color(
                (byte)Math.Min(255, color.RByte * colorLevel.R * lightLevel),
                (byte)Math.Min(255, color.GByte * colorLevel.G * lightLevel),
                (byte)Math.Min(255, color.BByte * colorLevel.B * lightLevel)
            );
        }

        return color;
    }

    /// <summary>
    /// Calculates light intensity as a function of time.
    /// </summary>
    public static double CalculateLightLevel(LightCycleComponent comp, float time)
    {
        var waveLength = MathF.Max(1, (float) comp.Duration.TotalSeconds);
        var crest = MathF.Max(0f, comp.MaxLightLevel);
        var shift = MathF.Max(0f, comp.MinLightLevel);
        return Math.Min(comp.ClipLight, CalculateCurve(time, waveLength, crest, shift, 6));
    }

    /// <summary>
    /// It is important to note that each color must have a different exponent, to modify how early or late one color should stand out in relation to another.
    /// This "simulates" what the atmosphere does and is what generates the effect of dawn and dusk.
    /// The blue component must be a cosine function with half period, so that its minimum is at dawn and dusk, generating the "warm" color corresponding to these periods.
    /// As you can see in the values, the maximums of the function serve more to define the curve behavior,
    /// they must be "clipped" so as not to distort the original color of the lighting. In practice, the maximum values, in fact, are the clip thresholds.
    /// </summary>
    public static Color CalculateColorLevel(LightCycleComponent comp, float time)
    {
        var waveLength = MathF.Max(1f, (float) comp.Duration.TotalSeconds);

        var red = MathF.Min(comp.ClipLevel.R,
            CalculateCurve(time,
                waveLength,
                MathF.Max(0f, comp.MaxLevel.R),
                MathF.Max(0f, comp.MinLevel.R),
                4f));

        var green = MathF.Min(comp.ClipLevel.G,
            CalculateCurve(time,
                waveLength,
                MathF.Max(0f, comp.MaxLevel.G),
                MathF.Max(0f, comp.MinLevel.G),
                10f));

        var blue = MathF.Min(comp.ClipLevel.B,
            CalculateCurve(time,
                waveLength / 2f,
                MathF.Max(0f, comp.MaxLevel.B),
                MathF.Max(0f, comp.MinLevel.B),
                2,
                waveLength / 4f));

        return new Color(red, green, blue);
    }

    /// <summary>
    /// Generates a sinusoidal curve as a function of x (time). The other parameters serve to adjust the behavior of the curve.
    /// </summary>
    /// <param name="x"> It corresponds to the independent variable of the function, which in the context of this algorithm is the current time. </param>
    /// <param name="waveLength"> It's the wavelength of the function, it can be said to be the total duration of the light cycle. </param>
    /// <param name="crest"> It's the maximum point of the function, where it will have its greatest value. </param>
    /// <param name="shift"> It's the vertical displacement of the function, in practice it corresponds to the minimum value of the function. </param>
    /// <param name="exponent"> It is the exponent of the sine, serves to "flatten" the function close to its minimum points and make it "steeper" close to its maximum. </param>
    /// <param name="phase"> It changes the phase of the wave, like a "horizontal shift". It is important to transform the sinusoidal function into cosine, when necessary. </param>
    /// <returns> The result of the function. </returns>
    public static float CalculateCurve(float x,
        float waveLength,
        float crest,
        float shift,
        float exponent,
        float phase = 0)
    {
        var sen = MathF.Pow(MathF.Sin((MathF.PI * (phase + x)) / waveLength), exponent);
        return (crest - shift) * sen + shift;
    }
}

/// <summary>
/// Raised when the offset on <see cref="LightCycleComponent"/> changes.
/// </summary>
[ByRefEvent]
public record struct LightCycleOffsetEvent(TimeSpan Offset)
{
    public readonly TimeSpan Offset = Offset;
}