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+---
+title: How the noise router and density functions work
+versions:
+  - '1.18.2'
+  - '1.19'
+tags:
+  - worldgen
+  - noise
+---
+
+[Density functions](/worldgen/density-function/) are used by the dimension generator to generate the terrain. They make up mathematical expressions that decide whether or not a block should be solid terrain.
+
+## Noise router
+The noise router is a piece of configuration in [noise settings](/worldgen/noise-settings/). It's a collection of density functions, some used for the biome layout, aquifers, or ore veins. The one that decides the terrain is **`final_density`**. This density function will be computed for every block position. If it returns a value greater than `0` the default block will be placed, otherwise either air or the default fluid will be placed.
+
+With this information we can make the most basic noise router, one where every density function is set to `0`. As predicted, this will result in a void world. Similarly, setting `"final_density": 1` will result in a world completely filled with stone.
+
+**`data/minecraft/worldgen/noise_settings/overworld.json`**
+```json
+{
+  "sea_level": 0,
+  "disable_mob_generation": false,
+  "aquifers_enabled": false,
+  "ore_veins_enabled": false,
+  "legacy_random_source": false,
+  "default_block": {
+    "Name": "minecraft:stone"
+  },
+  "default_fluid": {
+    "Name": "minecraft:water",
+    "Properties": {
+      "level": "0"
+    }
+  },
+  "noise": {
+    "min_y": 0,
+    "height": 256,
+    "size_horizontal": 2,
+    "size_vertical": 2
+  },
+  "noise_router": {
+    "barrier": 0,
+    "fluid_level_floodedness": 0,
+    "fluid_level_spread": 0,
+    "lava": 0,
+    "temperature": 0,
+    "vegetation": 0,
+    "continents": 0,
+    "erosion": 0,
+    "depth": 0,
+    "ridges": 0,
+    "initial_density_without_jaggedness": 0,
+    "final_density": 0,
+    "vein_toggle": 0,
+    "vein_ridged": 0,
+    "vein_gap": 0
+  },
+  "spawn_target": [],
+  "surface_rule": {
+    "type": "minecraft:sequence",
+    "sequence": []
+  }
+}
+```
+
+## Density function files
+In the above example all the density functions are constant numbers, but they don't have to be. Another option is to reference a density function file. Vanilla has some builtin density functions, for example:
+
+```json
+"final_density": "minecraft:overworld/base_3d_noise"
+```
+
+You can create your own density functions in the `worldgen/density_function` folder.
+
+## Complex density functions
+All the other density function types are defined as an object with a `"type"` field and optionally more fields. For example:
+```json
+{
+  "type": "minecraft:noise",
+  "noise": "minecraft:cave_entrance",
+  "xz_scale": 0.75,
+  "y_scale": 0.5
+}
+```
+<br/>
+The following is a list of all density functions in {#version#}
+
+### `abs`
+Calculates the absolute value of another density function.
+* `argument`: The input density function
+
+### `add`
+Adds two density functions together.
+* `argument1`: The first density function
+* `argument2`: The second density function
+
+### `beardifier`
+Adds beards for structures (see the `terrain_adaptation` field).
+
+*This density function has no extra fields*
+
+### `blend_alpha`
+
+*This density function has no extra fields*
+
+### `blend_density`
+* `argument`: The input density function
+
+### `blend_offset`
+
+*This density function has no extra fields*
+
+### `cache_2d`
+Only computes the input density once for each column, at Y=0
+* `argument`: The input density function
+
+### `cache_all_in_cell`
+Used in combination with [`interpolated`](#interpolated).
+* `argument`: The input density function
+
+### `cache_once`
+If this density function is referenced twice, it is only computed once per block position.
+* `argument`: The input density function
+
+### `clamp`
+Clamps the input between two values.
+* `input`: The input density function
+* `min`: The lower bound
+* `max`: The upper bound
+
+### `constant`
+A constant value. `{"type": "constant", "argument": 2}` is equivalent to `2`.
+* `argument`: The constant number
+
+### `cube`
+Cubes the input. (`x^3`)
+* `argument`: The input density function
+
+### `end_islands`
+
+*This density function has no extra fields*
+
+### `flat_cache`
+Similar to [`cache_2d`](#cache_2d) in that it only computes the input once for each column, but now at the first Y value that is requested.
+
+### `half_negative`
+If the input is negative, returns half of the input. Otherwise returns the input. (`x < 0 ? x/2 : x`)
+* `argument`: The input density function
+
+### `interpolated`
+Computes the input density at each of the 8 corners of a cell and interpolates between them. The size of a cell if determined by `size_horizontal * 4` and `size_vertical * 4`.
+* `argument`: The input density function
+
+### `max`
+Returns the maximum of two density functions.
+* `argument1`: The first density function
+* `argument2`: The second density function
+
+### `min`
+Returns the minimum of two density functions.
+* `argument1`: The first density function
+* `argument2`: The second density function
+
+### `mul`
+Multiplies two density functions.
+* `argument1`: The first density function
+* `argument2`: The second density function
+
+### `noise`
+The noise density function samples a noise.
+* `noise`: A reference to a `worldgen/noise` file
+* `xz_scale`: Scales the X and Z inputs before sampling
+* `y_scale`: Scales the Y input before sampling
+
+### `old_blended_noise`
+Uses a different kind of noise than [`noise`](#noise).
+* `xz_scale`
+* `y_scale`
+* `xz_factor`
+* `y_factor`
+* `smear_scale_multiplier`
+
+### `quarter_negative`
+If the input is negative, returns a quarter of the input. Otherwise returns the input. (`x < 0 ? x/4 : x`)
+* `argument`: The input density function
+
+### `range_choice`
+Computes the input value, and depending on that result returns one of two other density functions.
+* `input`: The input density function
+* `min_inclusive`: The lower bound of the range
+* `max_exclusive`: The upper bound of the range
+* `when_in_range`: Density function that will be returned when the input is inside the range
+* `when_out_of_range`: Density function that will be returned When the input is outside the range
+
+### `shift`
+Computes the input density at `(x/4, y/4, z/4)`.
+* `argument`: The input density function
+
+### `shift_a`
+Computes the input density at `(x/4, 0, z/4)`.
+* `argument`: The input density function
+
+### `shift_b`
+Computes the input density at `(z/4, x/4, 0)`.
+* `argument`: The input density function
+
+### `shifted_noise`
+Similar to [`noise`](#noise), but first shifts the input coordinates.
+* `noise`: A reference to a `worldgen/noise` file
+* `xz_scale`: Scales the X and Z inputs before sampling
+* `y_scale`: Scales the Y input before sampling
+* `shift_x`: Density function used to offset the X input
+* `shift_y`: Density function used to offset the Y input
+* `shift_z`: Density function used to offset the Z input
+
+### `spline`
+Computes a spline. More information about splines will follow in a future guide.
+* `spline`: The spline, can be either a number or an object:
+  * `coordinate`: The density function that will be used for the locations
+  * `points`: List of points of the cubic spline, cannot be empty
+    * `location`: Input value
+    * `value`: Output value, can be either a number or a spline object
+    * `derivative`: The slope at this point
+{#[1.18.2]
+* `min_value`: The minimum output value of the spline
+* `max_value`: The maximum output value of the spline
+#}
+
+### `square`
+Squares the input. (`x^2`)
+* `argument`: The input density function
+
+### `squeeze`
+First clamps the input between `-1` and `1`, then transforms it using `x/2 - x*x*x/24`.
+* `argument`: The input density function
+
+{#[1.18.2]
+### `terrain_shaper_spline`
+Computes a terrain shaper spline from the noise settings.
+* `spline`: The terrain shaper spline to use. One of `offset`, `factor`, or `jaggedness`
+* `min_value`: The minimum output value of the spline
+* `max_value`: The maximum output value of the spline
+* `continentalness`: The density function to use for the `continents` spline coordinate
+* `erosion`: The density function to use for the `erosion` spline coordinate
+* `weirdness`: The density function to use for the `weirdness` spline coordinate
+#}
+
+### `weird_scaled_sampler`
+* `rarity_value_mapper`: One of `type_1` or `type_2`
+* `noise`: A reference to a `worldgen/noise` file 
+* `input`: The input density function
+
+### `y_clamped_gradient`
+Returns the Y position after mapping it to a range.
+* `from_y`
+* `to_y`
+* `from_value`: The value to map `from_y` to
+* `to_value`: The value to map `to_y` to
diff --git a/src/styles/global.css b/src/styles/global.css
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@@ -1643,6 +1643,15 @@ hr {
 	font-size: 85%;
 }
 
+.guide-content h1 code,
+.guide-content h2 code,
+.guide-content h3 code,
+.guide-content h4 code,
+.guide-content h5 code,
+.guide-content h6 code {
+	font-size: 100%;
+}
+
 .guide-content pre > code {
 	display: block;
 	padding: 0.8em;