DayNightCycle

DayNightCycle

Game time that moves the sun, so an afternoon drive turns into a night drive.

What it does

DayNightCycle.core turns an hour into a lighting state: where the key light comes from, its colour and strength, the sky fill, the haze colour and how bright reflections are. It also gives one number for everything else, darkness, which is 0 at noon and 1 at midnight. Headlights and street lamps key off it.

The key light is the sun by day and the moon by night. Both use the same directional light, and the swap happens when both are at their dimmest, so the shadows never jump.

Use it in a scene

{
  "Sun": {
    "components": {
      "DirectionalLight": {
        "direction": [-0.4, -0.8, -0.3],
        "intensity": 4.8,
        "shadowEnabled": true,
        "shadowExtent": 64
      }
    }
  },
  "Ambient": {
    "components": {
      "HemisphericLight": { "intensity": 0.12 }
    }
  },
  "Sky": {
    "components": {
      "DayNightCycle": {
        "hour": 16.2,
        "hoursPerMinute": 2.5,
        "sun": "Sun",
        "ambient": "Ambient",
        "follow": "Player"
      }
    }
  }
}

It creates no lights. It picks up the handles the scene's lights announce and drives them every frame. Call registerDayNightCycleExtension(adapter) at bootstrap. Without it the clock still lights the scene, but reflections stay at daytime strength and skies does nothing.

Darkness from the hour

export function sunHeightAt(hour: number): number {
  return Math.sin(((wrapHour(hour) - 6) / 24) * Math.PI * 2);
}

/** 0 day .. 1 night. */
export function darknessAt(hour: number): number {
  return 1 - smoothstep(-0.14, 0.2, sunHeightAt(hour));
}

The sun's height is a sine wave that crosses the horizon at 6 and 18. Darkness stays at 0 until the sun is low, then climbs fast. At sunset it is 0.63, and about half an hour later it reaches 1. The whole dusk takes about 76 game minutes, which is under half a real minute at the default hoursPerMinute. With the default lightsOnAt, dayNight.nightfall fires at about 17:50.

HDR skies

Give it skies and it lights the scene with real sky photos (HDRIs) as the day turns:

{
  "Sky": {
    "components": {
      "DayNightCycle": {
        "sunIntensity": 4.8,
        "ambientDay": 0.12,
        "environmentDay": 0.6,
        "environmentNight": 0.3,
        "skies": [
          {
            "url": "/vehiclecombat/skies/qwantani_afternoon.env",
            "sunHeight": 0.65,
            "sunU": 0.6003,
            "level": 1
          },
          {
            "url": "/vehiclecombat/skies/qwantani_sunset.env",
            "sunHeight": 0.1,
            "sunU": 0.5999,
            "level": 1
          },
          {
            "url": "/vehiclecombat/skies/qwantani_dusk.env",
            "sunHeight": -0.06,
            "sunU": 0.6062,
            "level": 1.6
          },
          {
            "url": "/vehiclecombat/skies/qwantani_night.env",
            "sunHeight": -0.5,
            "sunU": 0.783,
            "level": 1
          }
        ]
      }
    }
  }
}

• url is a prefiltered .env sky. Make one from an .hdr with Babylon's EnvironmentTextureTools.CreateEnvTextureAsync.
• sunHeight is the sine of the sun's angle above the horizon when the photo was taken. The clock shows the sky shot nearest the current sun height.
• sunU is where the sun sits across the photo (0 at the left edge, 1 at the right). The sky is turned every frame so its sun lines up with the light casting the shadows. The glint on a car roof then agrees with its shadow.
• level evens out skies shot at different exposures.

All skies start loading at once, and a sky still loading is never put up, so a swap never flashes. With glossy, physically based materials the sky does most of the fill lighting, so keep the HemisphericLight low. The skies in the Endless Rampage scene are Poly Haven's CC0 "Qwantani" set by Greg Zaal and Jarod Guest.

If the scene also has an EnvironmentTexture, the DayNightCycle sky takes over as soon as its photo loads. EnvironmentTexture then only covers the first moments, and engines without the DayNight plugin.

Shadow box

A directional light's shadow covers a box centred on the light. Leave the light at the origin and a car three kilometres down the road has no shadow. So every frame the sun is moved to sit shadowDistance back up its own ray from the follow entity, a little ahead of the car.

Settings

Events

Needs

• DirectionalLight: plays both the sun and the moon.
• HemisphericLight: soft fill from above.
• MeshPrimitive: tells it where the car is.