# geometry

Note:This documentation is for the old 0.3.0 version of A-Frame. Check out the documentation for the current 0.8.0 version

The geometry component provides a basic shape for an entity. The general
geometry is defined by the `primitive`

property. Geometric primitives, in
computer graphics, means an extremely basic shape. With the primitive defined,
additional properties are used to further define the geometry. A material
component is usually 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 |

mergeTo | A selector to an entity to merge the entity’s geometry to. | None |

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 |

`mergeTo`

Merging geometries reduces the number of draw calls, greatly improving performance under certain circumstances. Geometries that are merged will inherit the material of the target geometry. Thus, it’s useful when we have entities that share the same material.

Once merged, the individual geometry can no longer be manipulated independently.

For geometry merging to be able to work, we will have to turn off `buffer`

and
turn on `skipCache`

.

<a-entity id="target" geometry="primitive: box; buffer: false; skipCache: true" material="color: red"></a-entity> |

## Built-in Geometries

`box`

The box geometry defines boxes (i.e., any quadilateral, 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 |

`circle`

The circle geometry creates flat two-dimensional circles. These can be complete
circles or partial circles (like Pac-Man). Note that because it is flat, only a
single side of the circle will be rendered if “side: double” is not specified
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 a double-sided material will be needed to render properly:

<!-- Tube --> |

We can create a cured 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 it is flat, only a single
side of the plane will be rendered unless `side: double`

is specified 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 |

`ring`

The ring geometry creates a flat ring, like a CD. Because it is flat,
only a single side of the ring will be rendered unless `side: double`

is
specified on 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 various 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, the particular shape of which
is defined by a pair of coprime integers, `p`

and `q`

. 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 |

## Register a Custom Geometry

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

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

. All
built-in geometries in A-Frame are registered using this API.

Here is how the `box`

geometry is registered.

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 the geometry needs to be created and set on
`this.geometry`

through the `init`

and `update`

lifecycle methods.

When a geometry component sets its `primitive`

property to the custom geometry
name, the properties of the custom geometry can be set 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 1, 2 2 2, 3 3 3"></a-entity> |