aframe

--- title: Building a Minecraft Demo type: guides layout: docs parent_section: guides order: 10 examples: - title: Aincraft src: https://github.com/aframevr/aframe/tree/master/examples/docs/aincraft/ --- [source-code]: https://github.com/aframevr/aframe/tree/master/examples/docs/aincraft/ [live-demo]: https://aframe.io/aframe/examples/docs/aincraft/ > View the [source code][source-code], or try out [the demo][live-demo] Let's build a basic Minecraft (voxel builder) demo that targets room scale VR with controllers (e.g., Quest, Vive, Rift). The example will be minimally usable on mobile and desktop.  ## Example Skeleton We'll start off with this skeleton HTML: ```html <script src="https://aframe.io/releases/1.7.1/aframe.min.js"></script> <body> <a-scene> </a-scene> </body> ``` ## 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 WebXR 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: ```html <script src="https://aframe.io/releases/1.7.1/aframe.min.js"></script> <a-scene> <a-cylinder id="ground" src="https://cdn.aframe.io/a-painter/images/floor.jpg" radius="32" height="0.1"></a-cylinder> </a-scene> ``` See a live version [here](https://aframe.io/aframe/examples/docs/aincraft/step1.html) ### Preloading Assets [assets]: https://aframe.io/docs/1.7.1/core/asset-management-system.html 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][assets]. 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: ```html <script src="https://aframe.io/releases/1.7.1/aframe.min.js"></script> <a-scene> <a-assets> <img id="groundTexture" src="https://cdn.aframe.io/a-painter/images/floor.jpg"> </a-assets> <a-cylinder id="ground" src="#groundTexture" radius="32" height="0.1"></a-cylinder> </a-scene> ``` See a live version [here](https://aframe.io/aframe/examples/docs/aincraft/step2.html) ## Adding a Background [a-sky]: https://aframe.io/docs/1.7.1/primitives/a-sky.html [flickr]: https://www.flickr.com/groups/equirectangular/ [gradient]: https://github.com/mrxz/fern-aframe-components/tree/main/sky-background Let's add a 360° background to our `<a-scene>` with the [`<a-sky>` element][a-sky]. `<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][flickr]. We could add a plain color background (e.g., `<a-sky color="#333"></a-sky>`) or [a gradient][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: ```html <script src="https://aframe.io/releases/1.7.1/aframe.min.js"></script> <a-scene> <a-assets> <img id="groundTexture" src="https://cdn.aframe.io/a-painter/images/floor.jpg"> <img id="skyTexture" src="https://cdn.aframe.io/a-painter/images/sky.jpg"> </a-assets> <a-cylinder id="ground" src="#groundTexture" radius="30" height="0.1"></a-cylinder> <a-sky id="background" src="#skyTexture" theta-length="90" radius="30"></a-sky> </a-scene> ``` See a live version [here](https://aframe.io/aframe/examples/docs/aincraft/step3.html) ## 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 [entity]: https://aframe.io/docs/1.7.1/core/entity.html Every single object in an A-Frame scene is [`<a-entity>`][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. [geometry]: https://aframe.io/docs/1.7.1/components/geometry.html [material]: https://aframe.io/docs/1.7.1/components/material.html 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: ```html  <a-entity geometry="primitive: box; depth: 0.5; height: 0.5; width: 0.5" material="color: red; shader: standard"></a-entity> ``` 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 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: ```js AFRAME.registerComponent('random-color', { init: function () { // ... } }); ``` [js]: https://aframe.io/docs/1.7.1/introduction/javascript-events-dom-apis.html 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][js]. 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. ```js AFRAME.registerComponent('random-color', { dependencies: ['material'], init: function () { // Set material component's color property to a random color. this.el.setAttribute('material', 'color', getRandomColor()); } }); function getRandomColor() { const letters = '0123456789ABCDEF'; var color = '#'; for (var i = 0; i < 6; i++ ) { color += letters[Math.floor(Math.random() * 16)]; } return 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: ```html <script src="https://aframe.io/releases/1.7.1/aframe.min.js"></script> <script src="components/random-color.js"></script> <a-scene> <a-assets> <img id="groundTexture" src="https://cdn.aframe.io/a-painter/images/floor.jpg"> <img id="skyTexture" src="https://cdn.aframe.io/a-painter/images/sky.jpg"> </a-assets>  <a-entity geometry="primitive: box; depth: 0.5; height: 0.5; width: 0.5" material="shader: standard" position="0 0.5 -2" random-color></a-entity> <a-cylinder id="ground" src="#groundTexture" radius="30" height="0.1"></a-cylinder> <a-sky id="background" src="#skyTexture" theta-length="90" radius="30"></a-sky> </a-scene> ``` See a live version [here](https://aframe.io/aframe/examples/docs/aincraft/step4.html) 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! ```html  <a-sphere random-color></a-sphere> <a-obj-model src="model.obj" random-color></a-obj-model> ``` [directory]: https://aframe.wiki/en/#!pages/component-directory.md if we wanted to share this component for other people to use, we could too. There is a community-maintained [Component Directory][directory] that lists many handy components from the ecosystem, similar to the Unity Asset Store. If we developed our application using components, all our code is inherently modular and reusable! ### Snap Component [snap]: https://github.com/aframevr/aframe/tree/master/examples/docs/aincraft/components/snap.js 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][snap] (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: ```html <a-entity geometry="primitive: box; height: 0.5; width: 0.5; depth: 0.5" material="shader: standard" random-color snap="offset: 0.25 0.25 0.25; snap: 0.5 0.5 0.5"></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 [mixin]: https://aframe.io/docs/1.7.1/core/mixins.html We can create [a mixin][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: ```html <script src="https://aframe.io/releases/1.7.1/aframe.min.js"></script> <script src="components/random-color.js"></script> <script src="components/snap.js"></script> <a-scene> <a-assets> <img id="groundTexture" src="https://cdn.aframe.io/a-painter/images/floor.jpg"> <img id="skyTexture" src="https://cdn.aframe.io/a-painter/images/sky.jpg"> <a-mixin id="voxel" geometry="primitive: box; height: 0.5; width: 0.5; depth: 0.5" material="shader: standard" random-color snap="offset: 0.25 0.25 0.25; snap: 0.5 0.5 0.5"></a-mixin> </a-assets> <a-cylinder id="ground" src="#groundTexture" radius="30" height="0.1"></a-cylinder> <a-sky id="background" src="#skyTexture" theta-length="90" radius="30"></a-sky> <a-entity mixin="voxel" position="-1 0 -2"></a-entity> <a-entity mixin="voxel" position="0 0 -2"></a-entity> <a-entity mixin="voxel" position="0 1 -2" animation="property: rotation; to: 0 360 0; loop: true"></a-entity> <a-entity mixin="voxel" position="1 0 -2"></a-entity> </a-scene> ``` And we've added voxels using that mixin: ```html <a-entity mixin="voxel" position="-1 0 -2"></a-entity> <a-entity mixin="voxel" position="0 0 -2"></a-entity> <a-entity mixin="voxel" position="0 1 -2" animation="property: rotation; to: 0 360 0; loop: true"></a-entity> <a-entity mixin="voxel" position="1 0 -2"></a-entity> ``` See a live version [here](https://aframe.io/aframe/examples/docs/aincraft/step5.html) 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: ```html  <a-entity vive-controls="hand: left"></a-entity> <a-entity vive-controls="hand: right"></a-entity>  <a-entity meta-touch-controls="hand: left"></a-entity> <a-entity meta-touch-controls="hand: right"></a-entity> ``` 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. ```html <a-entity id="teleHand" hand-controls="hand: left"></a-entity> <a-entity id="blockHand" hand-controls="hand: right"></a-entity> ``` ### Adding Teleportation to the Left Hand We'll plug in teleportation capabilities to the left hand such that we push a thumbstick to show an arc coming out of the controller, and let go of the thumbstick 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! To enable this, let's first define a `player` entity that wraps the controllers and the camera: ```html <script src="https://aframe.io/releases/1.7.1/aframe.min.js"></script>  <a-entity id="player"> <a-entity id="teleHand" hand-controls="hand: left"></a-entity> <a-entity id="blockHand" hand-controls="hand: right"></a-entity> <a-camera></a-camera> </a-entity> ``` [blink-controls]: https://github.com/jure/aframe-blink-controls For teleportation, there's a component called [blink-controls][blink-controls]. Following the README, we add the component via a `<script>` tag and just set the `blink-controls` component on the controller on the entity: ```html <script src="https://aframe.io/releases/1.7.1/aframe.min.js"></script> <script src="https://cdn.jsdelivr.net/npm/aframe-blink-controls/dist/aframe-blink-controls.min.js"></script>  <a-entity id="player"> <a-entity id="teleHand" hand-controls="hand: left"></a-entity> <a-entity id="blockHand" hand-controls="hand: right"></a-entity> <a-camera></a-camera> </a-entity> ``` By default, `blink-controls` will only teleport on the ground, but we can specify with `collisionEntities` to teleport on the blocks *and* the ground using selectors. This property is part of the API that the`blink-controls` component was created with: ```html <a-entity id="teleHand" hand-controls="hand: left" blink-controls="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 Component Directory][directory]. ### Adding Voxel Spawner to the Right Hand In WebXR, 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 `laser-controls` component for controller laser interaction that attaches the clicking laser to VR tracked controllers. Like the `blink-controls` component, we include the script tag and attach the `laser-controls` component. This time to the right hand: ```html <script src="https://aframe.io/releases/1.7.1/aframe.min.js"></script> <script src="https://cdn.jsdelivr.net/npm/aframe-blink-controls/dist/aframe-blink-controls.min.js"></script>  <a-entity id="teleHand" hand-controls="hand: left" blink-controls="collisionEntities: [mixin='voxel'], #ground"></a-entity> <a-entity id="blockHand" hand-controls="hand: right" laser-controls></a-entity> ``` Now when we pull the trigger button on the tracked controllers, `laser-controls` 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`: ```js document.querySelector('#blockHand').addEventListener(`click`, function (evt) { // Create a blank entity. var newVoxelEl = document.createElement('a-entity'); // Use the mixin to make it a voxel. newVoxelEl.setAttribute('mixin', 'voxel'); // Get normal of the face of intersection and scale it down a bit var normal = evt.detail.intersection.face.normal; normal.multiplyScalar(0.25); // Get the position of the intersection and add our scaled normal var position = evt.detail.intersection.point; position.add(normal); // Set the position using intersection point. The `snap` component above which // is part of the mixin will snap it to the closest half meter. newVoxelEl.setAttribute('position', position); // Add to the scene with `appendChild`. this.appendChild(newVoxelEl); }); ``` [intersection-spawn]: https://github.com/aframevr/aframe/tree/master/examples/docs/aincraft/components/intersection-spawn.js 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][intersection-spawn]. We attach `intersection-spawn` capabilities to the right hand, and it's also a good idea to give the raycaster a half-meter buffer to prevent voxels from spawning right at the controller: ```html <a-entity id="blockHand" hand-controls="hand: right" laser-controls raycaster="near: 0.5" 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! ```html <a-entity id="blockHand" hand-controls="hand: right" laser-controls raycaster="near: 0.5" intersection-spawn="event: click; mixin: voxel"></a-entity> <a-camera> <a-cursor intersection-spawn="event: click; mixin: voxel"></a-cursor> </a-camera> ``` ## Try It Out! > [Read the source code on GitHub][source-code]. > > [Try out the live version][live-demo] On desktop, we can drag to move the view and click to spawn blocks. We can also move using WASD. On mobile, we can pan the device around and tap to spawn blocks. If we have a VR headset with a [WebXR-capable browser][webxr] (e.g., Meta Quest, HTC Vive, Oculus Rift), we can view the [demo][live-demo] in VR within the browser. [webxr]: https://immersiveweb.dev/