Components and prefabs

Covers components added to a GameObject, placing and changing Unity-made prefabs, and the <Slot> syntax parts use to receive content.

Components you can add

There are 147 components you can add. Their attributes and values are in the Component list.

<Kiosk prefab="true">
  <Object name="Counter" position="0 0.5 0" static="batching lighting">
    <MeshFilter mesh="builtin:Cube"/>
    <MeshRenderer material="builtin:Default-Material" shadowCastingMode="TwoSided" receiveShadows="false"/>
    <BoxCollider size="1 1 1" center="0 0 0" isTrigger="false"/>
  </Object>
  <Object name="Lamp" position="0 2 0">
    <Light type="Spot" color="#FFE6CC" intensity="2.5" range="6" spotAngle="45" shadows="Soft" lightmapBakeType="Baked"/>
  </Object>
  <Object name="Speaker">
    <AudioSource playOnAwake="false" volume="0.5" loop="true" spatialBlend="1" minDistance="1" maxDistance="20"/>
  </Object>
</Kiosk>

Syntax	Number	Example
An enum value written lowercase (`point`)	`MOCHI1009`	enum-case
An attribute not in the table (`brightness`)	`MOCHI1005`	component-attribute

Material copies

Writing mainTexture or color on a MeshRenderer copies material’s .mat, and the renderer references a copy with the image and color set.

<Lamp prefab="true">
  <Object name="Bulb" position="0 2 0">
    <MeshFilter mesh="builtin:Sphere"/>
    <MeshRenderer material="../Art/Frame.mat" color="#FFE6CC" shadowCastingMode="Off"/>
    <Light type="Point" color="#FFE6CC" intensity="2.5" range="6"/>
  </Object>
</Lamp>


`material`	Required on the same `<MeshRenderer>`. Points to a project `.mat`. A built-in material (`builtin:Default-Material`) can’t be copied.
Property that’s set	The shader properties tagged `[MainTexture]` and `[MainColor]`. If none are found, `_MainTex` and `_Color`.
Copy’s name	`<original .mat name>_<path of the GameObject>.mat`. The path joins with `_` the `key` (or the `name` when there is none) of each GameObject from the root of the entry point down to that GameObject; a GameObject without a key directly inside a `<For>` puts the row keys before its name. Each GameObject gets a copy of its own
Where the copy is placed	The same generated-files folder as the prefab (generation on save).
Name collision	It’s an error when the copies of different GameObjects would get the same file name (names that differ only in upper and lower case, or only in characters a file name cannot have) and they set different images or colors. Rename one of them

Syntax	Number	Example
`mainTexture` with no `material`	`MOCHI1008`	texture-without-material
`color` written on a built-in material	`MOCHI2001`	builtin-material-color
Two GameObjects whose names differ only in case setting different images	`MOCHI4001`	same-name-different-image

Placing a prefab

<Prefab src="…"> places an instance of a prefab made in Unity. Its attributes and allowed children are in <Prefab>.

<Corner prefab="true">
  <Prefab src="../Kit/KitFrame.prefab" name="Frame A" position="2 1.5 0" scale="0.5 0.5 0.5">
    <Object name="Note" position="0 -0.5 0"/>
  </Prefab>
</Corner>


`position`	The value written on the `<Prefab>`. `0 0 0` when not written
`rotation`・`scale`・`active`・`static`	The prefab’s root value when not written (as when the prefab is placed in a scene in Unity). Writing a value replaces it
A model whose root is rotated on import	Placed facing the way Unity shows it. That rotation counts in layout, `inspect` and `gap`, as a written `rotation` does. Write `rotation="0 0 0"` to remove it
A prefab whose root is a RectTransform	Under a Canvas, `anchoredPosition` and the other RectTransform values stay the prefab’s when not written
UdonBehaviours inside	GameObjects inside a prefab have no key, so a GameObject with two or more UdonBehaviours cannot be pointed to by a path (`MOCHI1009`)

Changes inside a prefab

Changes inside a prefab (<At>, a component change, <Slot> with path) can only be written in a part’s file. To change one from the entry point, make a part that wraps the <Prefab> and use that.

<Wall prefab="true">
  <Framed position="0 1.5 0"/>
</Wall>
<!-- file: Assets/Example/Framed.mochi.xml -->
<Framed>
  <Prefab src="../Kit/KitFrame.prefab">
    <At path="Plate/Label" active="false"/>
    <At path="Canvas">
      <MeshRenderer material="../Art/Frame.mat"/>
    </At>
    <At path="Mount">
      <Object name="Spot">
        <Light type="Spot"/>
      </Object>
    </At>
  </Prefab>
</Framed>

<Wall prefab="true">
  <Prefab src="../Kit/KitFrame.prefab">
    <At path="Plate/Label" active="false"/>
  </Prefab>
</Wall>

Syntax	Number	Example
`<At>` written in the entry point file	`MOCHI3013`	override-in-entry
A path not in the prefab	`MOCHI2010`	at-path-not-found
A change to `<Light>` not on the prefab’s root	`MOCHI3010`	override-missing-component

Passing content with `<Slot>`

<Slot> is the place inside a part that receives the content the caller writes as children (attributes are in <Slot>).

<Board prefab="true">
  <Card>
    <Object name="Body"/>
    <Object name="Title" slot="title"/>
  </Card>
</Board>
<!-- file: Assets/Example/Card.mochi.xml -->
<Card>
  <Object name="Top"><Slot name="title"/></Object>
  <Object name="Bottom"><Slot/></Object>
</Card>


How to write content	Written as a child of the part’s tag. You can also write `slot` on children inside `<For>` and `<If>`.
Binding content	Reads the props and row of the file where the content is written. It can’t read the part’s props.
Content with nowhere to go	Is an error.

<Board prefab="true">
  <Framed>
    <Object name="Picture" slot="content"/>
  </Framed>
</Board>
<!-- file: Assets/Example/Framed.mochi.xml -->
<Framed>
  <Prefab src="../Kit/KitFrame.prefab">
    <Slot name="content" path="Mount"/>
  </Prefab>
</Framed>

Syntax	Number	Example
A `slot` name not in the part	`MOCHI2012`	slot-unknown
A default `<Slot/>` placed in two spots	`MOCHI3011`	slot-twice

Mount points

fill attaches the children added under the prefab’s root, one by one, to objects inside the prefab whose names match a pattern (mount points).

<Hall prefab="true">
  <Rooms/>
</Hall>
<!-- file: Assets/Example/Rooms.mochi.xml -->
<Rooms>
  <Prefab src="../Kit/KitRoom.prefab" fill="Mount*">
    <For each="art" in="folder('../Gallery/art/')">
      <Object key="{art.key}" name="{art.title}"/>
    </For>
  </Prefab>
</Rooms>


Patterns	`*` matches any run of characters, including none. It’s compared against the whole name.
Order of attachment	The order of a depth-first walk of the prefab’s hierarchy. Numbers in names aren’t read. In the example `KitRoom.prefab`, the order is `Mount1`, `Mount0`, `Mount3`, `Mount2`.
Children that are counted	Only children added under the prefab’s root. Children added with `<At>` and component changes aren’t counted.
Leftover mount points	Stay empty.
Not enough mount points	Is an error, unless `overflow="repeat"` is written.

Syntax	Number	Example
More children than mount points	`MOCHI3012`	too-many-to-fill

Repeated placement

Writing overflow="repeat" adds more instances of the same prefab to fill the rest, when there are more children than mount points.

<Hall prefab="true">
  <Prefab src="../Kit/KitRoom.prefab" fill="Mount*" overflow="repeat" gap="0 0 12">
    <For each="art" in="folder('../Gallery/art/')">
      <Object key="{art.key}" name="{art.title}"/>
    </For>
    <For each="row" in="table('../Data/art.csv')">
      <Object key="{row.key}" name="{row.title}"/>
    </For>
    <Object name="Guide"/>
  </Prefab>
</Hall>


`gap`	The offset (`x y z`) from one instance to the next. It is turned by the rotation of the original instance (the `rotation` written, or the rotation of the prefab’s root when not written) before it is applied
Name of an added instance	Continues as `original name (1)`, `original name (2)`.
Same as the original	Rotation, scale, active, and Static, plus, of the changes inside the prefab, component changes, `<At>`’s `active`, and components added with `add="true"` (a value that points to an object inside the prefab or to another added component points to the one in the same instance).
Only on the original instance	Children added with `<At>` and `<Slot path>`, and children placed in the mounts of the original instance. A component change or a component added with `add="true"` that points to one of these, or to anything under them, is an error (`MOCHI9001`). Pointing to an object inside the prefab points to that instance’s own object in each instance; an object outside the prefab is shared by all instances.
Checking whether `gap` is present	Only done once there are more children than mount points.

While there are enough mount points, missing gap isn’t an error.

<Hall prefab="true">
  <Prefab src="../Kit/KitRoom.prefab" fill="Mount*" overflow="repeat">
    <For each="art" in="folder('../Gallery/art/')">
      <Object key="{art.key}" name="{art.title}"/>
    </For>
  </Prefab>
</Hall>

Syntax	Number	Example
`overflow="repeat"` with no `gap`, when there are more children than mount points	`MOCHI1008`	repeat-without-gap