Custom Sky¶

Custom Sky changes the skybox texture and can apply different sets of skies depending on the time, biome, heights, weather, and more.

Place the file in:

• ~/sky/world0/ for Overworld.

• ~/sky/world1/ for End. (since version G9)

• ~/sky/world-1/ for Nether.

in the resource pack.

Each file represents one layer of the sky. OptiFine will load them in order by their number, applying one on top of the previous.

Additionally, two special properties files are applied to the sun and moon if present. This is mainly intended to allow overriding the blend method used by the sun and moon:

• ~/sky/world0/sun.properties: replaces sun.png.

• ~/sky/world0/moon_phases.properties: replaces moon_phases.png.

Instead of a full skybox, the source texture should match the layout of sun.png or moon_phases.png.

Properties¶

startFadeIn¶

Fade in/out times. All times are in hh:mm 24-hour format. See Time format.

If no times are specified, the layer is always rendered.

endFadeIn¶

endFadeOut¶

source¶

Path to source texture.

Multiple properties files can reuse the same source.

blend¶

The blending method between fading of layers.

Here, 'previous layer' can refer to the default sky or to the previous custom sky defined by sky<N-1>.properties. Supported blending methods are:

• add: Add this sky bitmap to the previous layer. In case of overflow, white is displayed.

• subtract: Subtracts this sky bitmap to the previous layer. In case of negative values, black is displayed.

• multiply: Multiply the previous RGBA values by the RGBA values in the current bitmap.

• dodge: Lightens the sky bitmap.

• burn: Darkens the sky bitmap.

• screen: Inverts both layers, multiplies them, and then inverts that result.

• replace: Replace the previous layer entirely with the current bitmap. There is no gradual fading with this method; if brightness computed from the fade times is >0, the full pixel value is used.

• overlay: RGB value > 0.5 brightens the image, < 0.5 darkens.

• alpha: Weighted average by alpha value.

rotate¶

Whether or not the source texture should rotate with the time of day.

speed¶

Rotation speed as a multiple of the default of one 360-degree cycle per game day.

A value of 0.5 rotates every two days.

axis¶

The axis of rotation of the skybox. If a player is looking in the given direction, the skybox will appear to be rotating clockwise around the line of sight.

Default rotation is along the southern axis (rising in the east and setting in the west).

For reference, the vectors corresponding to the six cardinal directions are below. However, the rotation axis can be any vector except 0.0 0.0 0.0:

down  =  0 -1  0
up    =  0  1  0
north =  0  0 -1
south =  0  0  1
west  = -1  0  0
east  =  1  0  0

days¶

The days for which the layer is to be rendered.

Days are numbered from 0 to daysLoop-1, for example: days=0 2-4 6.

daysLoop¶

Number of days in a loop, see above.

weather¶

Under what weather for which the layer is to be rendered. Several values can be specified separated by spaces, for example weather=clear rain thunder.

biomes¶

Limit the sky to only certain biomes.

heights¶

Limit the sky to only certain heights.

Since 1.18, negative values may be specified for height. When used in a range they have to be put in parenthesis ( ): (-3)-64.

transition¶

Transition time (in seconds) for the layer brightness. It is used to smooth sharp transitions, for example between different biomes.

Time format¶

All times are in hh:mm 24-hour format.

For reference,

The fade times control the brightness when blending.

• between startFadeIn and endFadeIn: 0 up to 1

• between endFadeIn and startFadeOut: always 1

• between startFadeOut and endFadeOut: 1 down to 0

• between endFadeOut and startFadeIn: always 0

Blender model¶

You can generate the vector coordinates that are required for the axis of rotation of the skybox by using a pre-made tool for Blender. It can be found here.

JSON schema¶

{
	"$schema": "http://json-schema.org/draft/2020-12/schema",
	"$id": "https://gitlab.com/whoatemybutter/optifinedocs/-/blob/master/schemas/custom_sky.schema.json",
	"title": "Custom Sky",
	"description": "Custom Sky changes the skybox texture and can apply different sets of skies depending on the time, biome, heights, weather, and more.",
	"type": "object",
	"properties": {
		"startFadeIn": {
			"type": "string",
			"pattern": "^\\d{1,2}:\\d{1,2}$",
			"description": "Start time to fade in."
		},
		"endFadeIn": {
			"type": "string",
			"pattern": "^\\d{1,2}:\\d{1,2}$",
			"description": "End time to fade in."
		},
		"endFadeOut": {
			"type": "string",
			"pattern": "^\\d{1,2}:\\d{1,2}$",
			"description": "End time to fade out."
		},
		"source": {
			"$ref": "common.schema.json#/$defs/resource",
			"description": "Path to source texture."
		},
		"blend": {
			"$ref": "common.schema.json#/$defs/blending_method_enum",
			"default": "add",
			"description": "The blending method between fading of layers."
		},
		"rotate": {
			"type": "boolean",
			"default": true,
			"description": "Whether or not the source texture should rotate with the time of day."
		},
		"speed": {
			"type": "number",
			"minimum": 0.0,
			"default": 1.0,
			"description": "Rotation speed as a multiple of the default of one 360-degree cycle per game day."
		},
		"axis": {
			"type": "string",
			"pattern": "^-?\\d+(\\.\\d+)? -?\\d+(\\.\\d+)? -?\\d+(\\.\\d+)?$",
			"default": "0.0 0.0 1.0",
			"description": "The axis of rotation of the skybox."
		},
		"days": {
			"type": "string",
			"description": "The days for which the layer is to be rendered."
		},
		"daysLoop": {
			"type": "integer",
			"minimum": 0,
			"default": 8,
			"description": "Number of days in a loop."
		},
		"weather": {
			"enum": ["clear", "rain", "thunder"],
			"default": "clear",
			"description": "Under what weather for which the layer is to be rendered."
		},
		"biomes": {
			"type": "string",
			"description": "Limit the sky to only certain biomes."
		},
		"heights": {
			"type": "string",
			"description": "Limit the sky to only certain heights."
		},
		"transition": {
			"type": "integer",
			"default": 1,
			"minimum": 0,
			"description": "Transition time in seconds for the layer brightness."
		}
	},
	"additionalProperties": false
}