Building a Minecraft Demo
Note: This documentation is for the old 0.8.0 version of A-Frame. Check out the documentation for the current 1.6.0 version
Let’s build a basic Minecraft (voxel builder) demo that targets room scale VR with controllers (e.g., Vive, Rift). The example will be minimally usable on mobile and desktop.
Example Skeleton
We’ll start off with this skeleton HTML:
<script src="https://aframe.io/releases/0.8.0/aframe.min.js"></script> |
Adding a Ground
<a-plane> and <a-circle> are basic primitives that are commonly used for
adding a ground. We’ll be using <a-cylinder> to better work with the
raycasters our controllers will be using. The cylinder will have a radius of 30
meters to match the radius of the sky we’ll add later. Note that A-Frame units
are in meters to match the real-world units returned from the WebVR API.
The texture of the ground we’ll be using is hosted at
https://cdn.aframe.io/a-painter/images/floor.jpg". We’ll add the texture to
our assets, and create a thin cylinder entity pointing to that texture:
See the Pen Minecraft VR Demo (Part 1) by mozvr (@mozvr) on CodePen.
<script src="https://aframe.io/releases/0.8.0/aframe.min.js"></script> |
Preloading Assets
Specifying a URL via the src attribute will load the texture at runtime.
Since network requests can negatively impact render performance, we can
preload the texture such that the scene doesn’t start rendering until its
assets have been fetched. We can do this using the asset management
system.
We place <a-assets> into our <a-scene>, place assets (e.g., images, videos,
models, sounds) into <a-assets>, and point to them from our entities via a
selector (e.g., #myTexture).
Let’s move our ground texture to <a-assets> to be preloaded using an
<img> element:
See the Pen Minecraft VR Demo (Part 2: Preloading Texture) by mozvr (@mozvr) on CodePen.
<script src="https://aframe.io/releases/0.8.0/aframe.min.js"></script> |
Adding a Background
Let’s add a 360° background to our <a-scene> with the <a-sky>
element. <a-sky> is a large 3D sphere with a material mapped on the
inside. Just like a normal image, <a-sky> can take an image path with src.
This ultimately lets us do immersive 360° images with one line of HTML. As
an exercise later, try using some 360° images from Flickr’s
equirectangular pool.
We could add a plain color background (e.g., <a-sky color="#333"></a-sky>) or
a gradient, but let’s add a textured background with an image. The
image we’re using is hosted at https://cdn.aframe.io/a-painter/images/sky.jpg.
The image texture we are using covers semi-sphere so we’ll chop our sphere in
half with theta-length="90", and we’ll give our sphere a radius of 30 meters
to match the ground:
See the Pen Minecraft VR Demo (Part 3: Adding a Background) by mozvr (@mozvr) on CodePen.
<script src="https://aframe.io/releases/0.8.0/aframe.min.js"></script> |
Adding Voxels
Voxels in our VR application will be like <a-box> but attached with a few
custom A-Frame components. But first let’s go over the entity-component
pattern. Let’s see how the easy-to-use primitives such as <a-box> are
composed under the hood.
This section will later do a deeper dive into the implementation of a couple A-Frame components. In practice though, we’d often get to use components via HTML already written by A-Frame community developers rather than building them from scratch.
Entity-Component Pattern
Every single object in an A-Frame scene is <a-entity>, which by itself
doesn’t do anything, like an empty <div>. We plug in components (not to be
confused with Web or React Components) to that entity to provide with
appearance, behavior , and logic.
For a box, we attach and configure A-Frame’s basic geometry and material
components. Components are represented as HTML attributes, and component
properties are defined like CSS styles by default. Here’s what <a-box> looks
like decomposed to its fundamental components. <a-box> wraps the components:
<!-- <a-box color="red" depth="0.5" height="0.5" shader="flat" width="0.5"></a-box> --> |
The benefit of components is that they are composable. We can mix and match from a bunch of existing components to construct different types of objects. In 3D development, the possible types of objects we construct are infinite in number and complexity, and we need an easy way of defining new types of objects rather than through traditional inheritance. Contrast this to the 2D web where we develop with a small pool of fixed HTML elements and plop them into a hierarchy.
Random Color Component
Components in A-Frame are defined in JavaScript, and they have full access to three.js and DOM APIs; they can do anything. We define all of our objects as a bundle of components.
We’ll put the pattern to action by writing an A-Frame component to set a random
color on our box. Components are registered with AFRAME.registerComponent. We
can define a schema, (the component’s data) and lifecycle handler methods (the
component’s logic). For the random color component, we’ll won’t be setting a schema
since it won’t be configurable. But we will define the init handler, which is
called exactly once when the component is attached:
AFRAME.registerComponent('random-color', { |
For the random color component, we want to set a random color on the entity
that this component is attached to. Components have a reference to the entity
with this.el from the handler methods. And to change the color with
JavaScript, we change the material component’s color property using
.setAttribute(). A-Frame enhances the behavior of several DOM APIs a bit, but the APIs mostly mirror
vanilla web development. Read more about using JavaScript and DOM APIs with
A-Frame.
We’ll also add the material component to the list of components that should
initialize before this one, just so our material isn’t overwritten.
AFRAME.registerComponent('random-color', { |
After the component is registered, we can attach this component straight from HTML. All code written within A-Frame’s framework is extending HTML, and those extensions can be used on other objects and in other scenes. The beautiful thing is that a developer could write a component that adds physics to an object, and then someone that doesn’t even know JavaScript could add physics to their scene!
Take our box entity from earlier, we attach the random-color HTML attribute
to plug in the random-color component. We’ll save the component as a JS file
and include it before the scene:
See the Pen Minecraft VR Demo (Part 4: Random Color Component) by mozvr (@mozvr) on CodePen.
<script src="https://aframe.io/releases/0.8.0/aframe.min.js"></script> |
Components can be plugged into any entity without having to create or extend a
class like we’d have to in traditional inheritance. If we wanted to attach it
to say, <a-sphere> or <a-obj-model>, we could!
<!-- Reusing and attaching the random color component to other entities. --> |
if we wanted to share this component for other people to use, we could too. We curate from many handy components from the ecosystem at the A-Frame Registry, similar to the Unity Asset Store. If we developed our application using components, all our code is inherently modular and reusable!
Snap Component
We’ll have a snap component to snap our boxes to a grid so they aren’t
overlapping. We won’t get into the details of how this component is
implemented, but you can check out the snap component’s source
code
(20 lines of JavaScript).
We attach the snap component to our box so that it snaps to every half meter, also with an offset to center the box:
<a-entity |
Now we have a box entity represented as a bundle of components that can be used to describe all the voxels in our scene.
Mixins
We can create a mixin to define a reusable bundle of components.
Instead of <a-entity>, which adds an object to the scene, we’ll describe it
using <a-mixin> which can be reused to create voxels like a prefab:
See the Pen Minecraft VR Demo (Part 5: Mixins) by mozvr (@mozvr) on CodePen.
<script src="https://aframe.io/releases/0.8.0/aframe.min.js"></script> |
And we’ve added voxels using that mixin:
<a-entity mixin="voxel" position="-1 0 -2"></a-entity> |
Next, we’ll be creating voxels dynamically through interaction using tracked controllers. Let’s start adding our hands to the application.
Adding Hand Controllers
Adding HTC Vive or Oculus Touch tracked controllers is easy:
<!-- Vive. --> |
We’ll be using hand-controls which abstracts and works with both Vive and
Rift controls, providing models of basic hand. We’ll make the left hand
responsible for teleporting around and the right hand responsible for spawning
and placing blocks.
<a-entity id="teleHand" hand-controls="left"></a-entity> |
Adding Teleportation to the Left Hand
We’ll plug in teleportation capabilities to the left hand such that we hold a button to show an arc coming out of the controller, and let go of the button to teleport to the end of the arc. Before, we wrote our own A-Frame components. But we can also use open source components already made from the community and just use them straight from HTML!
For teleportation, there’s a teleport-controls
component by @fernandojsg. Following the README, we
add the component via a <script> tag and just set the teleport-controls
component on the controller on the entity:
<script src="https://aframe.io/releases/0.8.0/aframe.min.js"></script> |
Then we’ll configure the teleport-controls component to use an arc type of
teleportation. By default, teleport-controls will only teleport on the
ground, but we can specify with collisionEntities to teleport on the blocks
and the ground using selectors. These properties are part of the API that the
teleport-controls component was created with:
<a-entity id="teleHand" hand-controls="left" teleport-controls="type: parabolic; collisionEntities: [mixin='voxel'], #ground"></a-entity> |
That’s it! One script tag and one HTML attribute and we can teleport. For more cool components, check out the A-Frame Registry.
Adding Voxel Spawner to the Right Hand
In WebVR, the ability to click on objects isn’t built-in as it is in 2D applications. We have to provide that ourselves. Fortunately, A-Frame has many components to handle interaction. A common method for cursor-like clicking in VR is to use a raycaster, a laser that shoots out and returns objects that it intersects with. Then we implement the cursor states by listening to interaction events and checking the raycaster for intersections.
A-Frame provides a gaze-based cursor for clicking by looking at objects, but
there’s also a controller-cursor component available that
attaches the clicking laser to VR tracked controllers. Like the
teleport-controls component, we include the script tag and attach the
controller-cursor component. This time to the right hand:
<script src="https://aframe.io/releases/0.8.0/aframe.min.js"></script> |
Now when we pull the trigger button on the tracked controllers,
controller-cursor will emit a click event on both the controller and the
entity it is intersecting at the time. Events such as mouseenter,
mouseleave are also provided. The event contains details about the
intersection.
That provides us with the ability to click, but we’ll have to wire up some code
to handle those clicks to spawn blocks. We can use an event listener and
document.createElement:
document.querySelector('#blockHand').addEventListener(`click`, function (evt) { |
To generalize creating entities from an intersection event, we’ve created an
intersection-spawn component that can be configured with any event and list
of properties. We won’t go into the detail of the implementation, but you can
check out the simple intersection-spawn component source code on
GitHub. We attach intersection-spawn capabilities to the
right hand:
<a-entity id="blockHand" hand-controls="right" controller-cursor intersection-spawn="event: click; mixin: voxel"></a-entity> |
Now when we click, we spawn voxels!
Adding Support for Mobile and Desktop
We see how we’ve built a custom type of object (i.e., a tracked hand controller
with a hand model that has click capabilities and spawns blocks on click) by
mixing together components. The wonderful thing with components is that they
are reusable in other contexts. We could even attach the intersection-spawn
component with the gaze-based cursor component so that we can also spawn
blocks on mobile and desktop, without changing a thing about the component!
<a-entity id="blockHand" hand-controls="right" controller-cursor intersection-spawn="event: click; mixin: voxel"></a-entity> |
Try It Out!
On desktop, we can drag and click to spawn blocks. On mobile, we can pan the device around and tap to spawn blocks. If we have a VR headset (e.g., HTC Vive, Oculus Rift + Touch), we can grab a WebVR-enabled browser and head over to the demo. Try it in VR by plugging in an HTC Vive or Oculus Rift and using a WebVR-enabled browser.
See the Pen Minecraft VR Demo (Final) by mozvr (@mozvr) on CodePen.
If we want to view what the experience looks like when used in VR from our desktop or mobile device, check out the demo with pre-recorded VR motion capture and gestures.