geometry
Note: This documentation is for the old 0.2.0 version of A-Frame. Check out the documentation for the current 1.4.0 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 alongside to provide a appearance alongside the shape to create a complete mesh.
Properties
We will go through the basic primitives and their respective properties one by one.
Property | Description | Default Value |
---|---|---|
primitive | One of box , circle , cone , cylinder , plane , ring , sphere , torus , torusKnot . |
None |
translate | Translates the geometry relative to its pivot point. | 0 0 0 |
Box
The box primitive 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 primitive defines two-dimensional circles, which 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 |
Cone
The cone primitive under the hood is a cylinder primitive with varying top and bottom radiuses.
<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 Primitive
The cylinder primitive can define cylinders in the traditional sense like a Coca-Cola™ can, but it can also define shapes such as tubes and curved surfaces. We’ll go over some of these cylinder recipes below.
Basic Cylinder
Traditional cylinders can be defined by using only a height and a radius:
<a-entity geometry="primitive: cylinder; height: 3; radius: 2"></a-entity> |
Tube
Tubes can be defined by making the cylinder open-ended, which removes the top and bottom surfaces of the cylinder such that the inside is visible. A double-sided material will be needed to render properly:
<!-- Tube --> |
Curved Surface
Curved surfaces can be defined by specifying the angle 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 |
Prisms
Other types of prisms can be defined by varying the number of radial segments (i.e., sides). For example, to make a hexagonal prism:
<!-- Hexagonal prism --> |
To play with an example of prism geometry, check out the Hexagon example on Codepen.
Plane
The plane primitive defines a flat surface. Note that because it is flat, only a single side of the plane will be rendered if side: double
is not specified on the material
component.
<a-entity geometry="primitive: plane; height: 10; width: 10" |
Property | Description | Default Value |
---|---|---|
width | Width along the X axis. | 1 |
height | Height along the Y axis. | 1 |
Ring
The ring geometry defines a flat ring, like a CD. Note that because it is flat, only a single side of the ring will be rendered if side: double
is not 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 primitive can define spheres in the traditional sense like a basketball. But it can also define various polyhedrons and abstract shapes given that it can specify the number of horizontal and vertical angles and faces.
Sticking with a basic sphere, the default number of segments is high enough to make the sphere appear round.
<a-entity geometry="primitive: sphere; radius: 2"></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 |
Torus
The torus primitive defines a donut 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 |
Torus Knot
The torus knot primitive defines 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 | Number that helps define the pretzel shape. | 2 |
q | Number that helps define the pretzel shape. | 3 |
thetaLength and thetaStart
In degrees, thetaStart
defines where to start a circle and thetaLength
defines where a circle 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 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.
translate
The translate
property translates the geometry. It is provided as a vec3. This is a useful short-hand for translating the geometry to effectively move its pivot point when running animations.
<!-- Translates the sphere such that its effective pivot point is at its bottom --> |
Defining Your Own Geometry
If there is a geometry that you need that is not provided by the standard geometry component, you can register your own geometry component. Later, we may introduce an API to register geometries:
`
js
AFRAME.registerComponent(‘my-geometry’, {
/ Called on component attach and data update. /
update: function () {
// Grab the mesh.
var mesh = this.el.getOrCreateObject3D(‘mesh’, THREE.Mesh);
// Provide your own geometry.
var geometry = mesh.geometry = new THREE.Geometry();
geometry.vertices.push(
new THREE.Vector3(-10, 10, 0),
new THREE.Vector3(-10, -10, 0),
new THREE.Vector3( 10, -10, 0)
);
geometry.faces.push(new THREE.Face3(0, 1, 2));
geometry.computeBoundingSphere();
},
/ Called on component detach. / remove: function () { this.el.getObject3D(‘mesh’).geometry = new THREE.Geometry(); } });