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 an appearance alongside the shape to create a complete mesh.

Overview of available geometries:

Base Properties

Every geometry type will have these properties:

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>

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>

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>

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 -->
<a-entity geometry="primitive: cylinder; openEnded: true" material="side: double"></a-entity>

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 -->
<a-entity geometry="primitive: cylinder; openEnded: true; thetaLength: 180"
          material="side: double"></a-entity>

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

<!-- Hexagonal prism -->
<a-entity geometry="primitive: cylinder; segmentsRadial: 6"></a-entity>

dodecahedron

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

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

octahedron

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

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

icosahedron

The icosahedron geometry creates a polygon with twenty equilateral triangular faces.

<a-entity geometry="primitive: icosahedron"></a-entity>

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>

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"
          material="side: double"></a-entity>

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>

tetrahedron

The tetrahedron geometry creates a polygon with four triangular faces.

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

torus

The torus geometry creates a donut or curved tube shape:

<!-- Half donut -->
<a-entity geometry="primitive: torus; radius: 2; radiusTubular: 0.5; arc: 180"></a-entity>

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>

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>

Register a Custom Geometry

We can register our own geometries using AFRAME.registerGeometry and creating an object that is an instance of THREE.BufferGeometry. Recent versions of three.js rename generators such as PlaneBufferGeometry to just PlaneGeometry, but support the old name as an alias. See the three.js manual to learn about creating a custom BufferGeometry. A-Frame registers all built-in geometries using this API. Here is how A-Frame registers the box geometry:

AFRAME.registerGeometry('box', {
  schema: {
    depth: {default: 1, min: 0},
    height: {default: 1, min: 0},
    width: {default: 1, min: 0},
    segmentsHeight: {default: 1, min: 1, max: 20, type: 'int'},
    segmentsWidth: {default: 1, min: 1, max: 20, type: 'int'},
    segmentsDepth: {default: 1, min: 1, max: 20, type: 'int'}
  },

  init: function (data) {
    this.geometry = new THREE.BoxGeometry(data.width, data.height, data.depth);
  }
});

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', {
  schema: {
    vertices: {
      default: ['-10 10 0', '-10 -10 0', '10 -10 0'],
    }
  },

  init: function (data) {
    var geometry = new THREE.BufferGeometry();
     const pointsArray = new Array();
     data.vertices.map(function (vertex) {
     var points = vertex.split(' ').map(function(x){return parseInt(x);});
     pointsArray.push(new THREE.Vector3(points[0], points[1], points[2]));
     });
     geometry.setFromPoints(pointsArray);
     geometry.computeBoundingBox();
     geometry.computeVertexNormals();
     this.geometry = geometry;
  }
});

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>