# Manifold Standard Version: 0.1.23 ### Abstract The Manifold Standard maps digital data to a space. It defines several types of JSON objects and how to reliably reconstruct the space from them. The reconstructed space contains a three-dimensional scene, and may specify how users can interact and leave traces in the scene. ### Status of This Memo This document is currently not open to the public. ### Relation to the reference implementations One of the reference implementations of the standard is the project [Exterior Space](http://extspace.net). Exterior Space is an open-source browser for spaces stored on-chain, planned to launch alongside the standard. Exterior Space implements the standard with its own profile for optional fields and modules. It also includes additional features optimized for browsing and editing spaces. Exterior Space supports the standard, and its major version aligns with the standard’s major version. The maintainers plan to extract the conformant core into a standalone open-source package as the reference implementation of the standard, which Exterior Space will then use. Until that is complete, this document will include footnotes about Exterior Space where relevant. ### 01 Table of Content This table of contents is provided as a guide for navigating this document. It does not list all the subsections, but only lists sections to a manageable depth for navigation. - [[00-Manifold-Standard]] - [[01-Table-of-Content]] - [[02-Copyright-Notice]] - [[03-Conventions]] - [[04-Version-Control]] - [[05-Conformance-Profile]] - [[10-Introduction]] - [[11-Scope-and-Structure]] ### 02 Copyright Notice Copyright (c) 2026 The Manifold Standard Editing Committee and the persons identified as the document authors. All rights reserved. ### 03 Conventions #### 03.01 Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [BCP 14](https://datatracker.ietf.org/doc/html/bcp14) [RFC2119](https://datatracker.ietf.org/doc/html/rfc2119) [RFC8174](https://datatracker.ietf.org/doc/html/rfc8174) when, and only when, they appear in all capitals, as shown here. #### 03.02 Conventions Used in This Document Any JSON object defined in this document MUST conform to [RFC8259](https://datatracker.ietf.org/doc/html/rfc8259). Some examples use the combination of a TypeScript single-line comment (`//`) followed by an ellipsis (`...`) as placeholder notation for content deemed irrelevant by the authors. These placeholders must of course be deleted or otherwise replaced, before attempting to validate the corresponding JSON code example. Whitespace is used in the examples inside this document to help illustrate the data structures, but it is not required. Unquoted whitespace is not significant in JSON. #### 03.03 Type Definitions In this document, a JSON object type defines the required and optional name-value pairs of a JSON object. An object belongs to a type — or "is of that type" — if it contains all required name-value pairs and only name-value pairs that are either required or optional for that type. Each name-value pair in a type definition specifies the name of the pair and the constraint on its value. Required name-value pairs are indicated by the keywords MUST or REQUIRED; optional name-value pairs by MAY, OPTIONAL, SHOULD, or RECOMMENDED, as defined in Section 03.01. A JSON type, or simply a type, is a constraint on a JSON value. A JSON object type, as defined above, is a type that constrains an object by specifying its required and optional name-value pairs. A type may also constrain a non-object value by specifying the set of allowed values, for example, a number within a particular range, or a string equal to one of a specified set. #### 03.04 Representation of Data In this document, TypeScript code is used to represent data, such as JSON object and JSON object type. However, the TypeScript code SHOULD NOT be considered the only form in which the data can be realized in an implementation. #### 03.99 Notes The section 03.02 significantly references the standard [RFC 7946](https://datatracker.ietf.org/doc/html/rfc7946). ### 04 Version Control In this section, the meaning and handling of the version of the standard are defined. #### 04.01 Version Number The version number of the standard and each section of the standard use the format MAJOR.MINOR.PATCH. Notice this is not the standard semantic versioning. 1. MAJOR version number is the released stable version of the standard. Each MAJOR bump is a release of a stable version, which is a closure of a set of proposed changes to the standard. Each MAJOR bump resets the MINOR version number to zero and increases the MAJOR version number by one. One can refer to a stable version of the standard by the MAJOR version number. For example, Manifold Standard Version 1 refers to Version 1.0.0 of the standard. 2. MINOR version numbers are used for proposed changes for the next stable version of the standard. Each MINOR bump is a closure of a set of section changes to the standard, with each change labeled with a PATCH version number. Each MINOR bump resets the PATCH version number to zero and increases the MINOR version number by one. 3. PATCH version numbers are used for proposed changes for the next stable version of one section of the standard. A PATCH bump of the standard is performed when a section of the standard is changed. This section is also marked with the full version number it was last changed. This mark can be referred to as the version number of this section. #### 04.02 Breaking Changes A breaking change is a change that either: 1. Makes the data format not backward compatible, or 2. Alters the relationship between the data and the reconstructed space in a non-compatible way. This includes changes of default behaviors. It is RECOMMENDED that stable releases of the standard do not introduce breaking changes. The version number does not imply whether changes are breaking or non-breaking. If a breaking change is included in a stable release, an attachment describing migration from the previous version to the current version MUST be provided in Section 90 of the release. #### 04.03 Notes on Implementation 1. Closure is an event of obtaining and confirming the consensus of the Manifold Standard Editing Committee. The Manifold Standard Editing Committee is the maintenance team for the Manifold Standard before version 1.0.0. Each closure MUST ends with a version number bump and a tag of the version to the Git repository. 2. If a change in one section requires edits in another section, and if the changes have a clear logical order, each edit SHOULD be followed by a PATCH bump. If term changes, typo changes, or convention changes occur in multiple sections, changes to multiple sections MAY be merged into one PATCH bump. If there is a set of inseparable changes across multiple sections, these changes MAY be merged into one PATCH bump. 3. A section of the standard is defined as one markdown file. #### 04.04 Implementation of Referencing 1. Each release of the stable version contains an archive action, for which the released standard MUST be uploaded to durable storage, obtaining the URI for referencing the standard of the particular stable version. 2. Each proposed version can be referred to using the git tag. 3. MINOR/PATCH version of the standard MUST NOT be cited as normative in external integrations. #### 04.05 Errata for Stable Releases Each post-release erratum of the stable release version is additional documentation called amendments to the stable release version, specifying fixes to the standard of the stable release version. The amended stable release version of the standard is referred to using the version number MAJOR.0.0.ERRATA. It is RECOMMENDED not to issue an erratum for the stable release version unless critical mistakes are made. The amendments MUST be uploaded to durable storage, obtaining the URI for referencing. #### 04.06 Expiration of This Section The version numbering, meaning, and handling described in this section are for versions before version 1.0.0. At version 1.0.0, versioning and change control transfer to the governance model that is defined at that time. The governance model after version 1.0.0 may or may not follow this handling of version numbers. ### 05 Conformance Profile TODO ## 10 Introduction The Manifold Standard specifies a mapping between a defined set of data and a space. Its goal is to define a virtual space where users can store, arrange, decorate, present, generate, update, and interact with digital assets. It provides a canonical data format for serializing these spaces and reliably reconstructing a space from that data. Although similar implementations exist in products and games, they remain closed and therefore fragment users’ memories, creations, and belongings, while a standard provides the common ground for decentralized, user-owned spaces open to anyone, anytime, anywhere, with any digital assets. The standard is organized into three parts that together define a framework enabling users to experience virtual spaces. The core specifications form the minimal kernel of the standard. They define the scene space and its artifacts, and hence how artifacts are placed within the scene. The extension specifications define how users are connected to the space, that is, how users present themselves and interact within and across spaces. Finally, modules are optional specifications built upon the core and extension specifications to enhance how users experience the space, providing additional layers of interaction, personalization, and growth. Together, the standard enables the space and its artifacts to encode users' live events, helps users share their spaces anywhere, assists users in discovering and engaging with other spaces, brings a sense of time or living creatures into the space, and much more. ### 11 Scope and Structure \[TODO\] ## 20 Core Specification The Core Specification defines objects that can be mapped to a scene and objects that represent assets which can be included in the scene. ### 21 Scene #### 21.01 Scene and `Coordinate` type A scene is a vector space of $\mathbb{R}^3$. We fix the right-handed orientation and an orthonormal basis, labeled $\hat x$, $\hat y$, and $\hat z$. A point in the space can be expressed as a 3-tuple $(x, y, z) = x\,\hat x + y\,\hat y + z\,\hat z$, where $x$, $y$, and $z$ are real numbers. A `Coordinate` type represents a point in the scene and is an array of three real numbers. It is represented as ```ts type Coordinate = [number, number, number] ``` where the three numbers correspond to $x$, $y$, and $z$, in this order. The ground plane is the subspace of the scene spanned by the basis $\hat x$ and $\hat y$, i.e., the set $\{(x, y, 0)\ |\ x \in \mathbb{R},\; y \in \mathbb{R}\}$. The up direction is defined as the positive direction of the basis vector $\hat z$. #### 21.02 Coordinate Transformation A coordinate transformation with uniform scale in the scene defined above transforms a vector $\vec v = (v_x, v_y, v_z)$ to $s\, R \, \vec v + \vec t$, where $R$ is a rotation operator, $s$ is a real number for uniform scale, and $\vec t$ is the translation of the origin. Such a transformation can therefore be encoded in three pieces of information: translation $\vec t$, rotation $R$, and scale $s$. ##### 21.02.01 Rotation and `Euler` Type Rotation can be represented by the type `Euler`, specifying the Euler angles as a 3-tuple $(x, y, z)$ in radians. The rotations are applied in the order of the $x$-axis, then the $y$-axis, then the $z$-axis. It can be represented as ```ts type Euler = [number, number, number] ``` where the three numbers correspond to rotation in radians around the $x$-axis, $y$-axis, and $z$-axis, in that order. For each rotation, a positive value means counterclockwise rotation. A zero rotation on all axes implies that the axes of the transformed coordinate align with those of the scene coordinate. ##### 21.02.02 Scale and `Scale` Type The type `Scale` represents the scaling of the transformed coordinate about its local origin and is a real number, where a value of 1 means no scaling. It can be represented as ```ts type Scale = number ``` ##### 21.02.03 Local Coordinate A coordinate distinct from the scene coordinate, also referred to as the global coordinate, is called a local coordinate. A local coordinate can be defined by the coordinate transformation above with respect to the scene coordinate, or can be specified by the origin of the local coordinate in the scene coordinate along with the transformed basis; see Section [[TODO: local scene]]. #### 21.03 Entity in the scene Each entity in the scene comes with its own local coordinate, and its placement can therefore be described by the three pieces of information defined in Section 21.02. That is, one starts with the entity's local coordinate coinciding with the scene coordinate, then applies the transformation defined in Section 21.02 to the entity. ### 22 `Form` Type Object A `Form` type object represents the layout of the scene. `Form` type is defined as ```ts interface Form { version: string // REQUIRED layout: Embedding[] // REQUIRED metadata?: FormMetadata // OPTIONAL properties?: FormProperties // OPTIONAL } ``` where - `version` is REQUIRED, and its value MUST be of type `string` equal to one of the standard’s version numbers (see Section [[04-Version-Control]]). - `layout` is REQUIRED, and its value MUST be an array of `Embedding`, representing placed artifacts in the space. An empty layout MUST have the value `[]`. - `metadata` is OPTIONAL, and its value MUST be of type `FormMetadata`. It is used to hold any additional descriptive data about the space. If not provided, an empty `FormMetadata` is used by default. - `properties` is OPTIONAL, and its value MUST be of type `FormProperties`. It represents additional properties of the scene. If not provided, an empty `FormProperties` is used by default. ### 23 `Embedding` Type Object An `Embedding` type object represents an artifact being placed in the scene. `Embedding` type is define as ```ts interface Embedding { artifact: Artifact // REQUIRED position: Coordinate // REQUIRED rotation: Euler // REQUIRED scale?: Scale //OPTIONAL properties?: EmbeddingProperties // OPTIONAL } ``` where - `artifact` is REQUIRED, and its value MUST be of type `Artifact`. - `position` is REQUIRED, and its value MUST be of type `Coordinate`. - `rotation` is REQUIRED, and its value MUST be of type `Euler`. - `scale` is OPTIONAL, and its value MUST be of type `Scale`. - `properties` is OPTIONAL, and its value MUST be of type `EmbeddingProperties`. It stores data that modifies or enhances the placed artifact. An `Embedding` type object represent an artifact been placed at `position` with `rotation` and `scale`, as defined in [[21-Scene#21.03 Entity in the scene]]. ### 24 `Artifact` Type Object The `Artifact` type object represents an asset that can be loaded into the space. `Artifact` type is defined as ```ts interface Artifact { content: string // REQUIRED type: ArtifactType // REQUIRED metadata: Metadata // RECOMMENDED } ``` where * `content` is REQUIRED, and stores the content to be loaded into the scene. * `type` is REQUIRED, and its value MUST be of type `ArtifactType`. It specifies the artifact type of `content` and therefore implies the possible loaders that an implementation can use to load the `content`. * `metadata` is RECOMMENDED, and its value MUST be of type `Metadata`. It stores relevant information about the asset. If it is not provided, the default MUST be used. #### 24.01 `ArtifactType` data The `ArtifactType` indicates the artifact type of the asset and therefore the loader that the implementation needs to use to correctly load it. Modules can define more `ArtifactType` values than those specified in this section. ```ts type ArtifactType = "model" ``` - For `model` artifact type, the implementation need to use a `GLTFLoader` to load the content, following the glTF standard. The artifact type, the `type` member of `Artifact`, and the `ArtifactType` type should not be confused with the JSON object type or JSON type. In this document, the single word "type" is reserved for JSON type. #### 24.02 Artifact Content The artifact content, as specified in the `content` field of the `Artifact` object, MUST be a path or Uniform Resource Locator (URL) to the data that can be loaded by the loader and presented in the scene. For artifact content of type `"model"`, it is RECOMMENDED that the data be a model file following the GLTF standard. When loaded, such a model contains a local origin. ### 25 `Metadata` Type Object The `Metadata` type object stores data relevant to an asset. All members in `Metadata` are OPTIONAL and if they are not specified, the default value will be used. Modules and extension specifications can define additional members in type `Metadata` beyond those specified in this section. It is RECOMMENDED that modules make use of the `attachment` and `properties`members rather than introducing new members in the `Metadata` type. `Metadata` type is define as ```ts interface Metadata { id: string, name: string, description: string, preview: string, creators: string[], attachment: ArtifactAttachment properties: ArtifactProperties // ... } ``` where * `id` MUST be of type `string` representing the path or asset ID of the artifact. Its default value is the `content` string of the artifact. It is RECOMMENDED that all artifacts loaded in the scene have distinct `id` values. * `name` MUST be of type `string` and is the display name of the artifact. Its default value is `"Artifact"`. * `description` MUST be of type `string` and is the display description of the artifact. Its default value is `""`, i.e., an empty string. * `preview` MUST be of type `string` containing the URL to the preview image file, and it is RECOMMENDED that the preview image file be of type PNG. * `creators` MUST be an array of `string` representing the creators of the artifact. * `attachment` MUST be of type `ArtifactAttachment`, representing any associated files relevant to this artifact. The `attachment` member is mainly used by modules and extension specifications. * `properties` MUST be of type `ArtifactProperties`. It stores data that modifies or enhances the artifact's behavior in the scene. The `properties` member is mainly used by modules and extension specifications. ### 26 Enhancing and Modifying the Scene From the `Form` data, one can reconstruct a scene by placing each artifact in `layout` according to its placement as specified in the `Embedding`. Modules can also add additional information to enhance or modify the scene by making use of the `FormMetadata`, `FormProperties`, and `EmbeddingProperties` types. These types by default include only empty objects, i.e., objects with no members, representing no additional or altered behavior beyond placing artifacts in the `layout` member. In this section, we go through some modules that can be used to enhance or modify the scene. These modules are not part of the core specification and implementations MAY implement them. #### 26.01 Form Metadata Module The Form Metadata module enhances the scene by adding descriptive data for the space, specified in the `FormMetadata` object. It is RECOMMENDED to include the following data to record basic information about the space: - `name` of type `string` - `description` of type `string` All other data in `FormMetadata` are OPTIONAL. An example of `FormMetadata` can be represented as: ```ts interface FormMetadata { name: string // RECOMMENDED description: string // RECOMMENDED // ... } ``` #### 26.02 Sky Module The Sky module enhances the scene by introducing two new members in `FormProperties` and a new artifact type, allowing a skybox to be specified for the scene. The new member in `FormProperties` is defined as ```ts interface FormProperties { sky: Artifact // OPTIONAL skyVisible: boolean // OPTIONAL // ... } ``` where * `sky` is OPTIONAL, and its value MUST be of type `Artifact` with artifact type `hdri`. * `skyVisible` is OPTIONAL, and its value MUST be of type `boolean`. If it is not provided, the default value `false` MUST be used. The new artifact type is defined as ```ts type ArtifactType = "hdri" // ... ``` and the implementation MUST use an `EXRLoader` to load the content, following the EXR standard. When `sky` in `FormProperties` is specified, a supported implementation MUST use the `content` of the specified artifact as the skybox of the scene. If the `sky` member is not provided, the implementation may use a default skybox or no skybox. When a skybox is present and `skyVisible` is `true`, the skybox MUST be rendered as the visible background. Otherwise, there MUST be no visible background rendered, and the skybox, if present, is used only for environment lighting and reflections. An implementation that does not support the Sky module MUST ignore the `sky` and `skyVisible` member of `FormProperties` and discard any artifact with artifact type `hdri`. When used with the Category module, the artifact MUST use `sky` as its artifact category. #### 26.03 Environment Model Module The Environment Model module enhances the scene by introducing a new member in `FormProperties`, allowing an environment model to be specified for the scene. The new member in `FormProperties` is defined as ```ts interface FormProperties { environmentModel: Artifact // OPTIONAL // ... } ``` where * `environmentModel` is OPTIONAL, and its value MUST be of type `Artifact` with artifact type `model`. When `environmentModel` in `FormProperties` is specified, a supported implementation MUST place the `content` of the specified artifact at the origin of the scene. If the `environmentModel` member is not provided, the implementation MUST NOT render any environment model. An implementation that does not support the Environment Model module MUST ignore the `environmentModel` member of `FormProperties`. When used with the Category module, the artifact MUST use `environment` as its artifact category. #### 26.04 Boundary Module and Tile Module ##### 26.04.01 `Coordinate2D` and `Euler2D` Types The 2-dimensional coordinate and rotation are represented by the types `Coordinate2D` and `Euler2D`, following the same conventions as the 3-dimensional ones defined in [[21-Scene]]. These types are defined as ```ts type Coordinate2D = [number, number] type Euler2D = number ``` where `Coordinate2D` represents the coordinate $(x, y)$, in that order, and a positive `Euler2D` value means counterclockwise rotation. ##### 26.04.02 Boundary Module The Boundary module modifies the scene by introducing a new member in `FormProperties`, defining a horizontal boundary of the scene. The new member in `FormProperties` is defined as ```ts interface FormProperties { boundary: OBB[] // OPTIONAL // ... } ``` where * `boundary` is OPTIONAL, and its value MUST be an array of `OBB` type objects. An `OBB` type object represents an oriented rectangle on the ground plane, defined by its `center`, its `rotation` about the center, and its `halfWidth` and `halfLength`. The `OBB` type is defined as ```ts interface OBB { center: Coordinate2D // REQUIRED rotation: Euler2D // REQUIRED halfWidth: number // REQUIRED halfLength: number // REQUIRED } ``` where - `center` is REQUIRED, and its value MUST be of type `Coordinate2D`. It represents the center of the oriented rectangle on the ground plane. - `rotation` is REQUIRED, and its value MUST be of type `Euler2D`. It represents the rotation of the rectangle about its center. - `halfWidth` is REQUIRED, and its value MUST be a `number`. It represents half the width of the rectangle, aligned with the $x$-axis at rotation 0. - `halfLength` is REQUIRED, and its value MUST be a `number`. It represents half the length of the rectangle, aligned with the $y$-axis at rotation 0. ##### 26.04.03 Tile Module The Tile module modifies the scene by introducing three new members in `FormProperties`, defining a tiled horizontal boundary of the scene. The new members in `FormProperties` are defined as ```ts interface FormProperties { tileList: Coordinate2D[] // OPTIONAL tileModel: Artifact // OPTIONAL tileVisible: boolean // OPTIONAL // ... } ``` where * `tileList` is OPTIONAL, and its value MUST be an array of `Coordinate2D`. It represents a tiled horizontal boundary of the scene as an array of positions of square tiles on the ground plane. * `tileModel` is OPTIONAL, and its value MUST be of type `Artifact`. It represents the visual representation of each tile in the scene. Its value MUST be ignored if `tileList` is not specified, or if `tileVisible` is `false`, or both. * `tileVisible` is OPTIONAL, and its value MUST be of type `boolean`. It represents the visibility toggle of the tile model. If it is not provided, the default value `true` MUST be used. Its value MUST be ignored if `tileList` is not specified. When `tileVisible` is `true` and `tileModel` is specified, the implementation MUST place `tileModel` at each position on the ground plane specified by `tileList` with zero rotation as the visual representation of each tile. When working with the Layout Mode module, the placed `tileModel` MUST NOT affect the reconstruction logic of the scene and MUST NOT appear in the `layout` data. When `tileVisible` is `true` and `tileModel` is not specified, the implementation MAY use its own `Artifact` as `tileModel` for the visual representation of the tile. It is RECOMMENDED to use a mid-tone gray plane with dimensions 1 by 1 as the default visual representation of each tile. When `tileVisible` is `false`, there MUST NOT be any visual representation of the tile and the value of `tileModel` MUST be ignored. When used with the Category module, the artifact that can be used as value of `tileModel` MUST use `tile` as its artifact category. ##### 26.04.04 Horizontal Boundary of the Scene A horizontal boundary of the scene is defined by a list of oriented rectangles, commonly referred to as oriented bounding boxes (OBBs), as defined in [[26.04-Boundary-Module-and-Tile-Module#26.02.02 Boundary Module]], lying on the ground plane. The union of the specified list of OBBs defines the inside of the scene, and any point that does not lie within this union is considered outside of the scene. The line where the outside and the inside of the scene meet is the scene boundary. For general artifacts, the ground plane $(x, y)$ placement, i.e., the projection of its $(x, y, z)$ placement onto the ground plane, MUST NOT lie outside of the scene. This means its $(x, y)$ placement may lie on the scene boundary by the definition of outside of the scene. Any artifact whose $(x, y)$ placement lies outside of the scene MUST be removed during reconstruction of the scene. When working with the Layout Mode module, for artifacts participating in stacking logic, no point of such an artifact's footprint MUST lie outside of the scene. That is, such artifacts in `layout` MUST be removed before the stacking logic is applied. When the Boundary module, the Tile module, or both are used, the boundary can be specified by the `boundary` member, the `tileList` member, or both, in `FormProperties`. When the boundary is specified by `boundary`, its value directly gives the OBBs of the boundary. When the boundary is specified by `tileList`, it is equivalent to a list of OBBs with zero rotation and width and length of 1, i.e., `halfWidth` and `halfLength` of 0.5, centered at each element of `tileList`. When both `boundary` and `tileList` are specified, the boundary is their intersection. When neither `boundary` nor `tileList` is specified, or both modules are not supported by the implementation, there is no boundary for the scene and every point in the scene is considered to lie within the boundary. One MUST NOT confuse the case where these data are specified as empty lists, which indicates that every point lies outside of the boundary, with the case where these data are not specified, which indicates that there is no boundary and every point in the scene lies within the boundary. Please note that this boundary is the boundary of the scene, not the boundary for avatar movement. For the boundary of avatar movement, please see [[TODO]]. #### 26.05 Layout Mode Module The Layout Mode module modifies the scene by introducing different layout modes. The original layout, i.e., each artifact placed in the scene with all possible positions, rotations, and scales as specified in the `Embedding` type object, is referred to as the freeform layout mode in the Layout Mode module. Other layout modes are restrictions on the freeform mode that are more suitable for particular uses of the space. Besides the freeform layout mode, four layout modes are specified, each with a two-dimensional and a three-dimensional version. Other modules can extend this module by introducing new layout modes. The layout modes defined by this module are: - Continuous layout mode - Discrete layout mode - Block layout mode - Slot layout mode The Layout Mode module introduces a few new members in `FormProperties`. The central member is the `layoutMode` member, defined as ```ts interface FormProperties { layoutMode: LayoutMode // OPTIONAL // ... } ``` where - `layoutMode` is OPTIONAL, and its value MUST be of type `LayoutMode`. It specifies which layout mode is used. If not provided, the freeform layout mode is used by default. The `LayoutMode` type is defined as ```ts type LayoutMode = | 'freeform' | 'continuous' | 'discrete' | 'block' | "slot" | 'flat-freeform' | 'flat-continuous' | 'flat-discrete' | 'flat-block' ``` where - `freeform` indicates the freeform layout mode in three dimensions. - `continuous` indicates the continuous layout mode in three dimensions. It does not have restrictions on position, but the placement must follow the stacking logic. - `discrete` indicates the discrete layout mode in three dimensions. It imposes a cell-placement rule and a stacking logic. - `block` indicates the block layout mode in three dimensions. It imposes a block-placement rule and allows only artifacts whose `volume` in each dimension is exactly 1 or an integer to be placed in the scene. - `slot` indicates the slot layout mode. It allows artifacts to be placed only at specified slots with specified orientations. - `flat-freeform` indicates the freeform layout mode in two dimensions. - `flat-continuous` indicates the continuous layout mode in two dimensions. - `flat-discrete` indicates the discrete layout mode in two dimensions. - `flat-block` indicates the block layout mode in two dimensions. The terms "cell-placement rule", "stacking logic", "block-placement rule", and "volume" will be defined throughout this section. Other modules extending this module can define more `LayoutMode` values than those specified in this section. Implementations supporting the Layout Mode module MAY support only one or more of the layout modes. Implementations SHOULD state which layout modes are supported. ##### 26.05.01 Reconstruction Logic The reconstruction logic takes a `Form` with a specified layout mode and outputs a `layout` following the specified layout mode restrictions, derived from the original `layout` in `Form`. The output `layout` is then used to reconstruct the scene by placing each artifact in the output `layout` according to its placement as specified in the `Embedding`. The reconstruction logic therefore refers to how to produce a `layout` following the restrictions from the original `layout`. ## 30 Extension Specification Extension Specifications define objects that represent users and their actions within the space, creating context for spaces and connections between users. ### 31 User and User Interface /[TODO/] A user is an being that must own or have access to an interface, and may have an inventory. Concretely, users include, but are not limited to, human beings, other intelligent beings, programs. #### Interface An interface is the input from a user to space and output to a user from space. The input from a user is a set of events that can trigger a set of corresponding functions known as interactions that changes the space. The output to a user is what user experienced from the space. ##### Camera Each user may be associated with a camera. The camera can be moved in response to interface interactions and serves as the user’s primary visual viewport. ##### External interface There are predefined sets of external interfaces commonly available on different platforms: - Desktop: - Mouse click (left or right) (at a place) - Mouse drag (along a path) - Keyboard input (with some characters) - Mobile: - Single tap and multi-tap (at places) - long tap (at a place) - Tap and drag (along a path) - On-screen keyboard input (with some characters) - System / Null users: - System interface: may monitor user-defined events occurring in the space or inventory as interfaces. - A null user is a system user that is implemented in a non-explicit way. ##### Avatar interface The avatar interface has two layers: the control layer and the avatar layer. The control layer is the external interface. When triggered, it calls an interaction function to control the avatar and perform a behavior. The avatar’s behavior then acts as an interface in the avatar layer. Common behaviors include: - Moving (towards a direction or along a path) - Standing (at a location) - Engaging (with an object, self, or another avatar, may with options) #### Inventory An inventory is a list of items associated with a user. It represents the set of artifacts currently held by the user. An inventory may include special slots that are monitored by system users. These are sometimes referred to as equipment slots or state slots. In implementation, inventory elements may correspond to items or tokens stored in a user's wallet, or to contextual contents such as a backpack. ##### Item Items are typically `Artifact` objects, but may be any object. They can also be monitored by system users. ### 32 Space /[TODO/] A space is the totality of what a user can experience. Concretely, a space can include the scene, its state, how it evolves and responds to user input, its recorded history, and any data stored within it along with how that data is presented. In this section we define a few potential constituents of a space besides the scene. The constituents defined here should not be considered the only possible parts of a space beyond the scene. #### State A state of the scene is #### UI Component #### Interaction #### Time #### History #### Background music and sounds effect