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325 lines
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325 lines
15 KiB
<!DOCTYPE html><html lang="en"><head>
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<meta charset="utf-8">
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<title>Billboards</title>
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<meta name="twitter:title" content="Three.js – Billboards">
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</head>
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<body>
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<div class="container">
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<div class="lesson-title">
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<h1>Billboards</h1>
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</div>
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<div class="lesson">
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<div class="lesson-main">
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<p>In <a href="canvas-textures.html">a previous article</a> we used a <a href="/docs/#api/en/textures/CanvasTexture"><code class="notranslate" translate="no">CanvasTexture</code></a>
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to make labels / badges on characters. Sometimes we'd like to make labels or
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other things that always face the camera. Three.js provides the <a href="/docs/#api/en/objects/Sprite"><code class="notranslate" translate="no">Sprite</code></a> and
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<a href="/docs/#api/en/materials/SpriteMaterial"><code class="notranslate" translate="no">SpriteMaterial</code></a> to make this happen.</p>
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<p>Let's change the badge example from <a href="canvas-textures.html">the article on canvas textures</a>
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to use <a href="/docs/#api/en/objects/Sprite"><code class="notranslate" translate="no">Sprite</code></a> and <a href="/docs/#api/en/materials/SpriteMaterial"><code class="notranslate" translate="no">SpriteMaterial</code></a></p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">function makePerson(x, labelWidth, size, name, color) {
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const canvas = makeLabelCanvas(labelWidth, size, name);
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const texture = new THREE.CanvasTexture(canvas);
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// because our canvas is likely not a power of 2
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// in both dimensions set the filtering appropriately.
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texture.minFilter = THREE.LinearFilter;
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texture.wrapS = THREE.ClampToEdgeWrapping;
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texture.wrapT = THREE.ClampToEdgeWrapping;
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- const labelMaterial = new THREE.MeshBasicMaterial({
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+ const labelMaterial = new THREE.SpriteMaterial({
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map: texture,
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- side: THREE.DoubleSide,
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transparent: true,
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});
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const root = new THREE.Object3D();
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root.position.x = x;
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const body = new THREE.Mesh(bodyGeometry, bodyMaterial);
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root.add(body);
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body.position.y = bodyHeight / 2;
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const head = new THREE.Mesh(headGeometry, bodyMaterial);
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root.add(head);
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head.position.y = bodyHeight + headRadius * 1.1;
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- const label = new THREE.Mesh(labelGeometry, labelMaterial);
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+ const label = new THREE.Sprite(labelMaterial);
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root.add(label);
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label.position.y = bodyHeight * 4 / 5;
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label.position.z = bodyRadiusTop * 1.01;
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</pre>
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<p>and the labels now always face the camera</p>
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<p></p><div translate="no" class="threejs_example_container notranslate">
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<div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/billboard-labels-w-sprites.html"></iframe></div>
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<a class="threejs_center" href="/manual/examples/billboard-labels-w-sprites.html" target="_blank">click here to open in a separate window</a>
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</div>
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<p></p>
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<p>One problem is from certain angles the labels now intersect the
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characters. </p>
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<div class="threejs_center"><img src="../resources/images/billboard-label-z-issue.png" style="width: 455px;"></div>
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<p>We can move the position of the labels to fix.</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">+// if units are meters then 0.01 here makes size
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+// of the label into centimeters.
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+const labelBaseScale = 0.01;
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const label = new THREE.Sprite(labelMaterial);
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root.add(label);
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-label.position.y = bodyHeight * 4 / 5;
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-label.position.z = bodyRadiusTop * 1.01;
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+label.position.y = head.position.y + headRadius + size * labelBaseScale;
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-// if units are meters then 0.01 here makes size
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-// of the label into centimeters.
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-const labelBaseScale = 0.01;
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label.scale.x = canvas.width * labelBaseScale;
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label.scale.y = canvas.height * labelBaseScale;
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</pre>
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<p></p><div translate="no" class="threejs_example_container notranslate">
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<div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/billboard-labels-w-sprites-adjust-height.html"></iframe></div>
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<a class="threejs_center" href="/manual/examples/billboard-labels-w-sprites-adjust-height.html" target="_blank">click here to open in a separate window</a>
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</div>
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<p></p>
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<p>Another thing we can do with billboards is draw facades.</p>
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<p>Instead of drawing 3D objects we draw 2D planes with an image
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of 3D objects. This is often faster than drawing 3D objects.</p>
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<p>For example let's make a scene with grid of trees. We'll make each
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tree from a cylinder for the base and a cone for the top.</p>
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<p>First we make the cone and cylinder geometry and materials that
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all the trees will share</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const trunkRadius = .2;
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const trunkHeight = 1;
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const trunkRadialSegments = 12;
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const trunkGeometry = new THREE.CylinderGeometry(
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trunkRadius, trunkRadius, trunkHeight, trunkRadialSegments);
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const topRadius = trunkRadius * 4;
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const topHeight = trunkHeight * 2;
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const topSegments = 12;
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const topGeometry = new THREE.ConeGeometry(
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topRadius, topHeight, topSegments);
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const trunkMaterial = new THREE.MeshPhongMaterial({color: 'brown'});
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const topMaterial = new THREE.MeshPhongMaterial({color: 'green'});
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</pre>
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<p>Then we'll make a function that makes a <a href="/docs/#api/en/objects/Mesh"><code class="notranslate" translate="no">Mesh</code></a> each for the trunk and top
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of a tree and parents both to an <a href="/docs/#api/en/core/Object3D"><code class="notranslate" translate="no">Object3D</code></a>.</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">function makeTree(x, z) {
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const root = new THREE.Object3D();
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const trunk = new THREE.Mesh(trunkGeometry, trunkMaterial);
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trunk.position.y = trunkHeight / 2;
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root.add(trunk);
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const top = new THREE.Mesh(topGeometry, topMaterial);
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top.position.y = trunkHeight + topHeight / 2;
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root.add(top);
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root.position.set(x, 0, z);
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scene.add(root);
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return root;
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}
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</pre>
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<p>Then we'll make a loop to place a grid of trees.</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">for (let z = -50; z <= 50; z += 10) {
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for (let x = -50; x <= 50; x += 10) {
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makeTree(x, z);
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}
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}
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</pre>
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<p>Let's also add a ground plane while we're at it</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">// add ground
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{
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const size = 400;
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const geometry = new THREE.PlaneGeometry(size, size);
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const material = new THREE.MeshPhongMaterial({color: 'gray'});
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const mesh = new THREE.Mesh(geometry, material);
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mesh.rotation.x = Math.PI * -0.5;
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scene.add(mesh);
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}
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</pre>
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<p>and change the background to light blue</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const scene = new THREE.Scene();
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-scene.background = new THREE.Color('white');
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+scene.background = new THREE.Color('lightblue');
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</pre>
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<p>and we get a grid of trees</p>
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<p></p><div translate="no" class="threejs_example_container notranslate">
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<div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/billboard-trees-no-billboards.html"></iframe></div>
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<a class="threejs_center" href="/manual/examples/billboard-trees-no-billboards.html" target="_blank">click here to open in a separate window</a>
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</div>
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<p></p>
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<p>There are 11x11 or 121 trees. Each tree is made from a 12 polygon
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cone and a 48 polygon trunk so each tree is 60 polygons. 121 * 60
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is 7260 polygons. That's not that many but of course a more detailed
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3D tree might be 1000-3000 polygons. If they were 3000 polygons each
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then 121 trees would be 363000 polygons to draw.</p>
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<p>Using facades we can bring that number down.</p>
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<p>We could manually create a facade in some painting program but let's write
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some code to try to generate one.</p>
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<p>Let's write some code to render an object to a texture
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using a <code class="notranslate" translate="no">RenderTarget</code>. We covered rendering to a <code class="notranslate" translate="no">RenderTarget</code>
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in <a href="rendertargets.html">the article on render targets</a>.</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">function frameArea(sizeToFitOnScreen, boxSize, boxCenter, camera) {
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const halfSizeToFitOnScreen = sizeToFitOnScreen * 0.5;
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const halfFovY = THREE.MathUtils.degToRad(camera.fov * .5);
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const distance = halfSizeToFitOnScreen / Math.tan(halfFovY);
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camera.position.copy(boxCenter);
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camera.position.z += distance;
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// pick some near and far values for the frustum that
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// will contain the box.
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camera.near = boxSize / 100;
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camera.far = boxSize * 100;
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camera.updateProjectionMatrix();
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}
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function makeSpriteTexture(textureSize, obj) {
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const rt = new THREE.WebGLRenderTarget(textureSize, textureSize);
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const aspect = 1; // because the render target is square
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const camera = new THREE.PerspectiveCamera(fov, aspect, near, far);
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scene.add(obj);
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// compute the box that contains obj
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const box = new THREE.Box3().setFromObject(obj);
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const boxSize = box.getSize(new THREE.Vector3());
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const boxCenter = box.getCenter(new THREE.Vector3());
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// set the camera to frame the box
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const fudge = 1.1;
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const size = Math.max(...boxSize.toArray()) * fudge;
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frameArea(size, size, boxCenter, camera);
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renderer.autoClear = false;
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renderer.setRenderTarget(rt);
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renderer.render(scene, camera);
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renderer.setRenderTarget(null);
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renderer.autoClear = true;
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scene.remove(obj);
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return {
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position: boxCenter.multiplyScalar(fudge),
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scale: size,
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texture: rt.texture,
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};
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}
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</pre>
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<p>Some things to note about the code above:</p>
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<p>We're using the field of view (<code class="notranslate" translate="no">fov</code>) defined above this code.</p>
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<p>We're computing a box that contains the tree the same way
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we did in <a href="load-obj.html">the article on loading a .obj file</a>
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with a few minor changes.</p>
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<p>We call <code class="notranslate" translate="no">frameArea</code> again adapted <a href="load-obj.html">the article on loading a .obj file</a>.
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In this case we compute how far the camera needs to be away from the object
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given its field of view to contain the object. We then position the camera -z that distance
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from the center of the box that contains the object.</p>
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<p>We multiply the size we want to fit by 1.1 (<code class="notranslate" translate="no">fudge</code>) to make sure the tree fits
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completely in the render target. The issue here is the size we're using to
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calculate if the object fits in the camera's view is not taking into account
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that the very edges of the object will end up dipping outside area we
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calculated. We could compute how to make 100% of the box fit but that would
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waste space as well so instead we just <em>fudge</em> it.</p>
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<p>Then we render to the render target and remove the object from
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the scene. </p>
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<p>It's important to note we need the lights in the scene but we
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need to make sure nothing else is in the scene.</p>
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<p>We also need to not set a background color on the scene</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const scene = new THREE.Scene();
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-scene.background = new THREE.Color('lightblue');
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</pre>
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<p>Finally we've made the texture we return it and the position and scale we
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need to make the facade so that it will appear to be in the same place.</p>
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<p>We then make a tree and call this code and pass it in</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">// make billboard texture
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const tree = makeTree(0, 0);
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const facadeSize = 64;
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const treeSpriteInfo = makeSpriteTexture(facadeSize, tree);
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</pre>
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<p>We can then make a grid of facades instead of a grid of tree models</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">+function makeSprite(spriteInfo, x, z) {
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+ const {texture, offset, scale} = spriteInfo;
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+ const mat = new THREE.SpriteMaterial({
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+ map: texture,
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+ transparent: true,
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+ });
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+ const sprite = new THREE.Sprite(mat);
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+ scene.add(sprite);
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+ sprite.position.set(
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+ offset.x + x,
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+ offset.y,
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+ offset.z + z);
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+ sprite.scale.set(scale, scale, scale);
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+}
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for (let z = -50; z <= 50; z += 10) {
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for (let x = -50; x <= 50; x += 10) {
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- makeTree(x, z);
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+ makeSprite(treeSpriteInfo, x, z);
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}
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}
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</pre>
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<p>In the code above we apply the offset and scale needed to position the facade so it
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appears the same place the original tree would have appeared.</p>
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<p>Now that we're done making the tree facade texture we can set the background again</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">scene.background = new THREE.Color('lightblue');
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</pre>
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<p>and now we get a scene of tree facades</p>
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<p></p><div translate="no" class="threejs_example_container notranslate">
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<div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/billboard-trees-static-billboards.html"></iframe></div>
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<a class="threejs_center" href="/manual/examples/billboard-trees-static-billboards.html" target="_blank">click here to open in a separate window</a>
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</div>
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<p></p>
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<p>Compare to the trees models above and you can see it looks fairly similar.
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We used a low-res texture, just 64x64 pixels so the facades are blocky.
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You could increase the resolution. Often facades are used only in the far
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distance when they are fairly small so a low-res texture is enough and
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it saves on drawing detailed trees that are only a few pixels big when
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far away.</p>
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<p>Another issue is we are only viewing the tree from one side. This is often
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solved by rendering more facades, say from 8 directions around the object
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and then setting which facade to show based on which direction the camera
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is looking at the facade.</p>
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<p>Whether or not you use facades is up to you but hopefully this article
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gave you some ideas and suggested some solutions if you decide to use them.</p>
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</div>
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</div>
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</div>
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<script src="/manual/resources/prettify.js"></script>
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