# geometry

The geometry component provides a basic shape for an entity. The `primitive`

property defines the general shape. Geometric primitives, in computer graphics,
are irreducible basic shapes. A material component is commonly defined to
provide a appearance alongside the shape to create a complete mesh.

## Base Properties

Every geometry type will have these properties:

Property | Description | Default Value |
---|---|---|

buffer | Transform geometry into a BufferGeometry to reduce memory usage at the cost of being harder to manipulate. | true |

primitive | Name of a geometry (e.g., one of the geometries listed below). Determines the geometry type and what other properties are available. | box |

skipCache | Disable retrieving the shared geometry object from the cache. | false |

## Built-in Geometries

`box`

The box geometry defines boxes (i.e., any quadrilateral, not just cubes).

<a-entity geometry="primitive: box; width: 1; height: 1; depth: 1"></a-entity> |

Property | Description | Default Value |
---|---|---|

width | Width (in meters) of the sides on the X axis. | 1 |

height | Height (in meters) of the sides on the Y axis. | 1 |

depth | Depth (in meters) of the sides on the Z axis. | 1 |

segmentsDepth | Number of segmented faces on the z-axis | 1 |

segmentsHeight | Number of segmented faces on the y-axis | 1 |

segmentsWidth | Number of segmented faces on the x-axis | 1 |

`circle`

The circle geometry creates flat two-dimensional circles. These can be complete
circles or partial circles (like Pac-Man). Note that because circles are flat,
A-Frame will only render a single face of the circle if we don’t specify ```
side:
double
```

on the `material`

component.

<a-entity geometry="primitive: circle; radius: 1" material="side: double"></a-entity> |

Property | Description | Default Value |
---|---|---|

radius | Radius (in meters) of the circle. | 1 |

segments | Number of triangles to construct the circle, like pizza slices. A higher number of segments means the circle will be more round. | 32 |

thetaStart | Start angle for first segment. Can be used to define a partial circle. | 0 |

thetaLength | The central angle (in degrees). Defaults to `360` , which makes for a complete circle. |
360 |

`thetaLength`

and `thetaStart`

Properties

In degrees, `thetaStart`

defines where to start a circle or arc and
`thetaLength`

defines where a circle or arc ends. If we wanted to make a `(`

shape, we would start the circle halfway through and define the length as half
of a circle. We can do this with `thetaStart: 180; thetaLength: 180`

. Or if we
wanted to make a `)`

shape, we can do `thetaStart: 0; thetaLength: 180`

.

Useful cases might be to animating `thetaStart`

to create a spinner effect or
animating `thetaLength`

on a fuse-based cursor for visual feedback.

`cone`

The cone geometry is a cylinder geometry that have different top and bottom radii.

<a-entity geometry="primitive: cone; radiusBottom: 1; radiusTop: 0.1"></a-entity> |

Property | Description | Default Value |
---|---|---|

height | Height of the cone. | 2 |

openEnded | Whether the ends of the cone are open (true) or capped (false). | false |

radiusBottom | Radius of the bottom end of the cone. | 1 |

radiusTop | Radius of the top end of the cone. | 1 |

segmentsRadial | Number of segmented faces around the circumference of the cone. | 36 |

segmentsHeight | Number of rows of faces along the height of the cone. | 18 |

thetaStart | Starting angle in degrees. | 0 |

thetaLength | Central angle in degrees. | 360 |

`cylinder`

The cylinder geometry creates cylinders in the traditional sense like a Coca-Cola™ can, but it can also define shapes such as tubes and curved surfaces.

We can create a basic cylinder using height and radius:

<a-entity geometry="primitive: cylinder; height: 3; radius: 2"></a-entity> |

We can create a tube by making the cylinder open-ended, which removes the top and bottom surfaces of the cylinder such that the inside is visible. Then we need a double-sided material to render properly:

<!-- Tube --> |

We can create a curved surfaces by specifying the arc via `thetaLength`

such
that the cylinder doesn’t curve all the way around, making the cylinder
open-ended, and then making the material double-sided:

<!-- Curved surface --> |

Property | Description | Default Value |
---|---|---|

radius | Radius of the cylinder. | 1 |

height | Height of the cylinder. | 2 |

segmentsRadial | Number of segmented faces around the circumference of the cylinder. | 36 |

segmentsHeight | Number of rows of faces along the height of the cylinder. | 18 |

openEnded | Whether the ends of the cylinder are open (true) or capped (false). | false |

thetaStart | Starting angle in degrees. | 0 |

thetaLength | Central angle in degrees. | 360 |

We can create prisms by changing the number of radial segments (i.e., sides). For example, to make a hexagonal prism:

<!-- Hexagonal prism --> |

`dodecahedron`

The dodecahedron geometry creates a polygon with twelve equally-sized faces.

<a-entity geometry="primitive: dodecahedron; radius: 2"></a-entity> |

Property | Description | Default Value |
---|---|---|

radius | Radius (in meters) of the dodecahedron. | 1 |

`octahedron`

The octahedron geometry creates a polygon with eight equilateral triangular faces.

<a-entity geometry="primitive: octahedron"></a-entity> |

Property | Description | Default Value |
---|---|---|

radius | Radius (in meters) of the tetrahedron. | 1 |

`plane`

The plane geometry creates a flat surface. Because planes are flat, A-Frame
will render only a single face of the plane unless we specify `side: double`

on
the `material`

component.

<a-entity geometry="primitive: plane; height: 10; width: 10" material="side: double"></a-entity> |

Property | Description | Default Value |
---|---|---|

width | Width along the X axis. | 1 |

height | Height along the Y axis. | 1 |

segmentsHeight | Number of segmented faces on the y-axis | 1 |

segmentsWidth | Number of segmented faces on the x-axis | 1 |

`ring`

The ring geometry creates a flat ring, like a CD. Because the ring is
flat, A-Frame will only render a single face of the ring unless we specify ```
side:
double
```

the `material`

component.

<a-entity geometry="primitive: ring; radiusInner: 0.5; radiusOuter: 1" |

Property | Description | Default Value |
---|---|---|

radiusInner | Radius of the inner hole of the ring. | 1 |

radiusOuter | Radius of the outer edge of the ring. | 1 |

segmentsTheta | Number of segments. A higher number means the ring will be more round. | 32 |

segmentsPhi | Number of triangles within each face defined by segmentsTheta. | 8 |

thetaStart | Starting angle in degrees. | 0 |

thetaLength | Central angle in degrees. | 360 |

`sphere`

The sphere geometry creates spheres (e.g., balls). We can create a basic sphere:

<a-entity geometry="primitive: sphere; radius: 2"></a-entity> |

We can create polyhedrons and abstract shapes by specifying the number of horizontal angles and faces:

<a-entity geometry="primitive: sphere; segmentsWidth: 2; segmentsHeight: 8"></a-entity> |

Property | Description | Default Value |
---|---|---|

radius | Radius of the sphere. | 1 |

segmentsWidth | Number of horizontal segments. | 18 |

segmentsHeight | Number of vertical segments. | 36 |

phiStart | Horizontal starting angle. | 0 |

phiLength | Horizontal sweep angle size. | 360 |

thetaStart | Vertical starting angle. | 0 |

thetaLength | Vertical sweep angle size. | 360 |

`tetrahedron`

The tetrahedron geometry creates a polygon with four triangular faces.

<a-entity geometry="primitive: tetrahedron; radius: 2"></a-entity> |

Property | Description | Default Value |
---|---|---|

radius | Radius (in meters) of the tetrahedron. | 1 |

`torus`

The torus geometry creates a donut or curved tube shape:

<!-- Half donut --> |

Property | Description | Default Value |
---|---|---|

radius | Radius of the outer edge of the torus. | 1 |

radiusTubular | Radius of the tube. | 0.2 |

segmentsRadial | Number of segments along the circumference of the tube ends. A higher number means the tube will be more round. | 36 |

segmentsTubular | Number of segments along the circumference of the tube face. A higher number means the tube will be more round. | 32 |

arc | Central angle. | 360 |

`torusKnot`

The torus knot geometry creates a pretzel shape. A pair of coprime integers,
`p`

and `q`

, defines the particular shape of the pretzel. If `p`

and `q`

are
not coprime the result will be a torus link:

<a-entity geometry="primitive: torusKnot; p: 3; q:7"></a-entity> |

Property | Description | Default Value |
---|---|---|

radius | Radius that contains the torus knot. | 1 |

radiusTubular | Radius of the tubes of the torus knot. | 0.2 |

segmentsRadial | Number of segments along the circumference of the tube ends. A higher number means the tube will be more round. | 36 |

segmentsTubular | Number of segments along the circumference of the tube face. A higher number means the tube will be more round. | 32 |

p | How many times the geometry winds around its axis of rotational symmetry. | 2 |

q | How many times the geometry winds around a circle in the interior of the torus. | 3 |

`triangle`

The triangle geometry creates a flat two-dimensional triangle. Because triangles are flat,
A-Frame will render only a single face, which is the one with `vertexA`

, `vertexB`

, and
`vertexC`

appear in counterclockwise order on the screen, unless we specify `side: double`

on
the `material`

component.

<a-entity geometry="primitive: triangle" material="side: double"></a-entity> |

Property | Description | Default Value |
---|---|---|

vertexA | Coordinates of one of the three vertices | 0 0.5 0 |

vertexB | Coordinates of one of the three vertices | -0.5 -0.5 0 |

vertexC | Coordinates of one of the three vertices | 0.5 -0.5 0 |

## Register a Custom Geometry

We can register our own geometries using `AFRAME.registerGeometry`

and creating
an object that is an instance of `THREE.Geometry`

. A-Frame
registers all built-in geometries using this API. Here is how A-Frame registers
the `box`

geometry:

AFRAME.registerGeometry('box', { |

Like with registering components, we provide a name, a
schema that will expose the properties of the geometry, and
lifecycle methods. Then we need to create the geometry and set on
`this.geometry`

through the `init`

lifecycle method.

When a geometry component sets its `primitive`

property to the custom geometry
name, we can set the properties of the custom geometry on the geometry
component. Say we registered a custom geometry:

AFRAME.registerGeometry('example', { |

We can then use that custom geometry in HTML:

<a-entity geometry="primitive: example; vertices: 1 1 -3, 3 1 -3, 2 2 -3"></a-entity> |