Title: Three.js Fundamentals Description: Your first Three.js lesson starting with the fundamentals This is the first article in a series of articles about three.js. [Three.js](http://threejs.org) is a 3D library that tries to make it as easy as possible to get 3D content on a webpage. Three.js is often confused with WebGL since more often than not, but not always, three.js uses WebGL to draw 3D. WebGL is a very low-level system that only draws points, lines, and triangles. To do anything useful with WebGL generally requires quite a bit of code and that is where three.js comes in. It handlings things like scenes, lights, shadows, materials, textures, all things that you'd have to write yourself if you were to use WebGL directly. These tutorials assume you already know JavaScript and, for the most part they will use ES6 style JavaScript. Most browsers that support three.js are auto-updated so most users should be able to run this code. If you'd like to make this code run on older browsers look into a transpiler like [Babel](http://babel.io). When learning most programming languages the first thing people do is make the computer print `"Hello World!"`. For 3D one of the most common first things to do is to make a 3D cube. so let's start with "Hello Cube!" The first thing we need is a `` tag so ``` ``` Three.js will draw into that canvas so we need to look it up and pass it to three.js. ``` ``` Note there are some esoteric details here. If you don't pass a canvas into three.js it will create one for you but then you have to add it to your document. Where to add it may change depending on your use case and you'll have to change your code so I find that passing a canvas to three.js feels a little more flexible. I can put the canvas anywhere and the code will find it where as if I had code to insert the canvas into to the document I'd likely have to change that code if my use case changed. After we look up the canvas we create a `WebGLRenderer`. The renderer is the thing responsible for actually taking all the data you provide and rendering it to the canvas. In the past there have been other renderers like `CSSRenderer`, a `CanvasRenderer` and in the future there may be a `WebGL2Renderer` or `WebGPURenderer`. For now there's the `WebGLRenderer` that uses WebGL to render 3D to the canvas. Next up we need a camera. ``` const fov = 75; const aspect = 2; // the canvas default const zNear = 0.1; const zFar = 5; const camera = new THREE.PerspectiveCamera(fov, aspect, zNear, zFar); ``` `fov` is short for `field of view`. In this case 75 degrees in the vertical dimension. Note that most angles in three.js are in radians but for some reason the perspective camera takes degrees. `aspect` is the display aspect of the canvas. We'll go over the details in another article but by default a canvas is 300x150 pixels which makes the aspect 300/150 or 2. `zNear` and `zFar` represent the space in front of the camera that will be rendered. Anything before that range or after that range will be clipped (not drawn). Those 4 settings define a *"frustum"*. A *frustum* is the name of a 3d shape that is like a pyramid with the tip sliced off. In other words think of the word "frustum" as another 3D shape like sphere, cube, prism, frustum. The height of the zNear and zFar planes are determined by the field of view. The width of both planes is determined by the field of view and the aspect. Anything inside the defined frustum will be be drawn. Anything outside will not. The camera defaults to looking down the -Z axis with +Y up. We'll put our cube at the origin so we need to move the camera back a litte from the origin in order to see anything. ``` camera.position.z = 2; ``` Here's what we're aiming for. In the diagram above we can see our camera is at `z = 2`. It's looking down the -Z axis. Our frustum starts 0.1 units from the front of the camera and goes to 5 units in front of the camera. Because in this diagram we are looking down, the field of view is affected by the aspect. Our canvas is twice as wide as it is tall so across view the field of view will be much wider than our specified 75 degrees which is the vertical field of view. Next we make a `Scene`. A `Scene` in three.js is a form of scene graph. Anything you want three.js to draw needs to be added to the scene. We'll cover more details of how scenes work in a future article. ``` const scene = new THREE.Scene(); ``` Next up we create a `BoxGeometry` which contains the data for a box. Almost anything we want to display in Three.js needs geometry which defines the vertices that make up our 3D object. ``` const boxWidth = 1; const boxHeight = 1; const boxDepth = 1; const geometry = new THREE.BoxGeometry(boxWidth, boxHeight, boxDepth); ``` We then create a basic material and set its color. Colors can be specified using standard CSS style 6 digit hex color values. ``` const material = new THREE.MeshBasicMaterial({color: 0x44aa88}); ``` We then create a `Mesh`. A `Mesh` in three represents the combination of a `Geometry` (the shape of the object) and a `Material` (how to draw the object, shiny or flat, what color, what texture(s) to apply. Etc.) as well as the position, orientation, and scale of that object in the scene. ``` const cube = new THREE.Mesh(geometry, material); ``` And finally we add that mesh to the scene ``` scene.add(cube); ``` We can then render the scene by calling the renderer's render function and passing it the scene and the camera ``` renderer.render(scene, camera); ``` Here's a working exmaple {{{example url="../threejs-fundamentals.html" }}} It's kind of hard to tell that is a 3D cube since we're viewing it directly down the -Z axis and the cube itself is axis aligned so we're only seeing a single face. Let's animate it spinning and hopefully that will make it clear it's being drawn in 3D. To animate it we'll render inside a render loop using [`requestAnimationFrame`](https://developer.mozilla.org/en-US/docs/Web/API/window/requestAnimationFrame). Here's our loop ``` function render(time) { time *= 0.001; // convert time to seconds cube.rotation.x = time; cube.rotation.y = time; renderer.render(scene, camera); requestAnimationFrame(render); } requestAnimationFrame(render); ``` `requestAnimationFrame` is a request to the browser that you want to animate something. You pass it a function to be called. In our case that function is `render`. The browser will call your function and if you update anything related to the display of the page the browser will re-render the page. In our case we are calling three's `renderer.render` function which will draw our scene. `requestAnimationFrame` passes the time since the page started rendering to the our function. That time is passed in milliseconds. I find it's much easier to work with seconds so here we're converting that to seconds. We then set the cube's X and Y rotation to the current time. These rotations are in [radians](https://en.wikipedia.org/wiki/Radian). There are 2 pi radians in a circle so our cube should turn around once on each axis in about 6.28 seconds. We then render the scene and request another animation frame to continue our loop. Outside the loop we call `requestAnimationFrame` one time to start the loop. {{{example url="../threejs-fundamentals-with-animation.html" }}} It's a little better but it's still hard to see the 3d. What would help is to add some lighting so let's add a light. There are many kinds of lights in three.js which we'll go over in a future article. For now let's create a directional light. ``` { const color = 0xFFFFFF; const intensity = 1; const light = new THREE.DirectionalLight(color, intensity); light.position.set(-1, 2, 4); scene.add(light); } ``` Directional lights have a position and a target. Both default to 0, 0, 0. In our case we're setting the light's position to -1, 2, 4 so it's slightly on the left, above, and behind our camera. The target is still 0, 0, 0 so it will shine toward the origin. We also need to change the material. The `MeshBasicMaterial` is not affected by lights. Let's change it to a `MeshPhongMaterial` which is affected by lights. ``` -const material = new THREE.MeshBasicMaterial({color: 0x44aa88}); // greenish blue +const material = new THREE.MeshPhongMaterial({color: 0x44aa88}); // greenish blue ``` And here it is working. {{{example url="../threejs-fundamentals-with-light.html" }}} It should now be pretty clearly 3D. Just for the fun of it let's add 2 more cubes. We'll use the same geometry for each cube but make a different material so each cube can be a different color. First we'll make a function that creates a new material with the specified color. Then it creates a mesh using the specified geometry and adds it to the scene and sets its X position. ``` function makeInstance(geometry, color, x) { const material = new THREE.MeshPhongMaterial({color}); const cube = new THREE.Mesh(geometry, material); scene.add(cube); cube.position.x = x; return cube; } ``` Then we'll call it 3 times with 3 different colors and X positions saving the `Mesh` instances in an array. ``` const cubes = [ makeInstance(geometry, 0x44aa88, 0), makeInstance(geometry, 0x8844aa, -2), makeInstance(geometry, 0xaa8844, 2), ]; ``` Finally we'll spin all 3 cubes in our render function. We compute a slightly different rotation for each one. ``` function render(time) { time *= 0.001; // convert time to seconds cubes.forEach((cube, ndx) => { const speed = 1 + ndx * .1; const rot = time * speed; cube.rotation.x = rot; cube.rotation.y = rot; }); ... ``` and here's that. {{{example url="../threejs-fundamentals-3-cubes.html" }}} If you compare it to the top down diagram above you can see it matches our expectections. With cubes at X = -2 and X = +2 they are partially outside our frustum. They are also somewhat exaggeratedly warped since the field of view across the canvas is so extreme. I hope this short intro helps to get things started. [Next up we'll cover making our code responsive so it is adaptable to multiple situations](threejs-responsive.html).