What is Three.js?

Let's try to describe it briefly:
Three.js is a library that makes WebGL - 3D in the browser - easy to use. While a simple cube in raw WebGL would turn out hundreds of lines of Javascript and shader code, a Three.js equivalent is only a fraction of that.

Before we start

Before you can use Three.js, you need somewhere to display it. Save the following HTML to a file on your computer, along with a copy ofthree.min.js in the js/ directory, and open it in your browser.
<html> <head> <title>My first Three.js app</title> <style> body { margin: 0; } canvas { width: 100%; height: 100% } </style> </head> <body> <script src="js/three.min.js"></script> <script> // Our Javascript will go here. </script> </body> </html>
That's all. All the code below goes into the empty <script> tag.

Creating the scene

To actually be able to display anything with Three.js, we need three things: A scene, a camera, and a renderer so we can render the scene with the camera.
 var scene = new THREE.Scene(); var camera = new THREE.PerspectiveCamera( 75, window.innerWidth / window.innerHeight, 0.1, 1000 ); var renderer = new THREE.WebGLRenderer(); renderer.setSize( window.innerWidth, window.innerHeight ); document.body.appendChild( renderer.domElement );
Let's take a moment to explain what's going on here. We have now set up the scene, our camera and the renderer. There are a few different cameras in Three.js. For now, let's use a PerspectiveCamera. The first attribute is the field of view.
The second one is the aspect ratio. You almost always want to use the width of the element divided by the height, or you'll get the same result as when you play old movies on a widescreen TV - the image looks squished.
The next two attributes are the near and far clipping plane. What that means, is that objects further away from the camera than the value of far or closer than near won't be rendered. You don't have to worry about this now, but you may want to use other values in your games to get better performance.
Next up is the renderer. This is where the magic happens. In addition to the WebGLRenderer we use here, Three.js comes with a few others, often used as fallbacks for users with older browsers or for those who don't have WebGL support for some reason.
In addition to creating the renderer instance, we also need to set the size at which we want it to render our app. It's a good idea to use the width and height of the area we want to fill with our game - in this case, the width and height of the browser window. For performance intensive games, you can also give setSize smaller values, like window.innerWidth/2 and window.innerHeight/2, for half the resolution. This does not mean that the game will only fill half the window, but rather look a bit blurry and scaled up.
Last but not least, we add the renderer element to our HTML document. This is a <canvas> element the renderer uses to display the scene to us.
"That's all good, but where's that cube you promised?" Let's add it now.

var geometry = new THREE.BoxGeometry( 1, 1, 1 ); var material = new THREE.MeshBasicMaterial( { color: 0x00ff00 } ); var cube = new THREE.Mesh( geometry, material ); scene.add( cube ); camera.position.z = 5;

To create a cube, we need a BoxGeometry. This is an object that contains all the points (vertices) and fill (faces) of the cube. We'll explore this more in the future.
In addition to the geometry, we need a material to color it. Three.js comes with several materials, but we'll stick to the MeshBasicMaterialfor now. All materials take an object of properties which will be applied to them. To keep things very simple, we only supply a color attribute of 0x00ff00, which is green. This works the same way that colors work in CSS or Photoshop (hex colors).
The third thing we need is a Mesh. A mesh is an object that takes a geometry, and applies a material to it, which we then can insert to our scene, and move freely around.
By default, when we call scene.add(), the thing we add will be added to the coordinates (0,0,0). This would cause both the camera and the cube to be inside each other. To avoid this, we simply move the camera out a bit.

Rendering the scene

If you copied the code from above into the HTML file we created earlier, you wouldn't be able to see anything. This is because we're not actually rendering anything yet. For that, we need what's called a render loop.

function render() { requestAnimationFrame( render ); renderer.render( scene, camera ); } render();

This will create a loop that causes the renderer to draw the scene 60 times per second. If you're new to writing games in the browser, you might say "why don't we just create a setInterval? The thing is - we could, but requestAnimationFrame has a number of advantages. Perhaps the most important one is that it pauses when the user navigates to another browser tab, hence not wasting their precious processing power and battery life.

Animating the cube

If you insert all the code above into the file you created before we began, you should see a green box. Let's make it all a little more interesting by rotating it.
Add the following right above the renderer.render call in your render function:
 cube.rotation.x += 0.1; cube.rotation.y += 0.1;
This will be run every frame (60 times per second), and give the cube a nice rotation animation. Basically, anything you want to move or change while the game / app is running has to go through the render loop. You can of course call other functions from there, so that you don't end up with a render function that's hundreds of lines.

The result

Congratulations! You have now completed your first Three.js application. It's simple, you have to start somewhere.
The full code is available below. Play around with it to get a better understanding of how it works.
 <html> <head> <title>My first Three.js app</title> <style> body { margin: 0; } canvas { width: 100%; height: 100% } </style> </head> <body> <script src="js/three.min.js"></script> <script> var scene = new THREE.Scene(); var camera = new THREE.PerspectiveCamera( 75, window.innerWidth/window.innerHeight, 0.1, 1000 ); var renderer = new THREE.WebGLRenderer(); renderer.setSize( window.innerWidth, window.innerHeight ); document.body.appendChild( renderer.domElement ); var geometry = new THREE.BoxGeometry( 1, 1, 1 ); var material = new THREE.MeshBasicMaterial( { color: 0x00ff00 } ); var cube = new THREE.Mesh( geometry, material ); scene.add( cube ); camera.position.z = 5; var render = function () { requestAnimationFrame( render ); cube.rotation.x += 0.1; cube.rotation.y += 0.1; renderer.render(scene, camera); }; render(); </script> </body> </html>

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