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