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.
Every geometry type will have these properties:
Transform geometry into a BufferGeometry to reduce memory usage at the cost of being harder to manipulate.
A selector to an entity to merge the entity’s geometry to.
Name of a geometry (e.g., one of the geometries listed below). Determines the geometry type and what other properties are available.
Disable retrieving the shared geometry object from the cache.
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
For geometry merging to be able to work, we will have to turn off buffer and
turn on skipCache.
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.
Number of triangles to construct the circle, like pizza slices. A higher number of segments means the circle will be more round.
Start angle for first segment. Can be used to define a partial circle.
The central angle (in degrees). Defaults to 360, which makes for a complete circle.
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.
The cone geometry is a cylinder geometry that have different top and bottom radii.
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:
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 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: