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POthreejs fragment shader using recycled frame buffers
 

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  1. POthreejs fragment shader using recycled frame buffers
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    <p>I'm trying to make an app that will simulate long exposure photography. The idea is that I grab the current frame from the webcam and composite it onto a canvas. Over time, the photo will 'expose', getting brighter and brighter. (see <a href="http://www.chromeexperiments.com/detail/light-paint-live-mercury/?f=" rel="nofollow noreferrer">http://www.chromeexperiments.com/detail/light-paint-live-mercury/?f=</a>)</p> <p>I have a shader that works perfectly. It's just like the 'add' blend mode in photoshop. The problem is that I can't get it to recycle the previous frame. </p> <p>I thought that it would be something simple like <code>renderer.autoClear = false;</code> but that option seems to do nothing in this context.</p> <p>Here's the code that uses THREE.EffectComposer to apply the shader.</p> <pre><code> onWebcamInit: function () { var $stream = $("#user-stream"), width = $stream.width(), height = $stream.height(), near = .1, far = 10000; this.renderer = new THREE.WebGLRenderer(); this.renderer.setSize(width, height); this.renderer.autoClear = false; this.scene = new THREE.Scene(); this.camera = new THREE.OrthographicCamera(width / -2, width / 2, height / 2, height / -2, near, far); this.scene.add(this.camera); this.$el.append(this.renderer.domElement); this.frameTexture = new THREE.Texture(document.querySelector("#webcam")); this.compositeTexture = new THREE.Texture(this.renderer.domElement); this.composer = new THREE.EffectComposer(this.renderer); // same effect with or without this line // this.composer.addPass(new THREE.RenderPass(this.scene, this.camera)); var addEffect = new THREE.ShaderPass(addShader); addEffect.uniforms[ 'exposure' ].value = .5; addEffect.uniforms[ 'frameTexture' ].value = this.frameTexture; addEffect.renderToScreen = true; this.composer.addPass(addEffect); this.plane = new THREE.Mesh(new THREE.PlaneGeometry(width, height, 1, 1), new THREE.MeshBasicMaterial({map: this.compositeTexture})); this.scene.add(this.plane); this.frameTexture.needsUpdate = true; this.compositeTexture.needsUpdate = true; new FrameImpulse(this.renderFrame); }, renderFrame: function () { this.frameTexture.needsUpdate = true; this.compositeTexture.needsUpdate = true; this.composer.render(); } </code></pre> <p>Here is the shader. Nothing fancy.</p> <pre><code> uniforms: { "tDiffuse": { type: "t", value: null }, "frameTexture": { type: "t", value: null }, "exposure": { type: "f", value: 1.0 } }, vertexShader: [ "varying vec2 vUv;", "void main() {", "vUv = uv;", "gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );", "}" ].join("\n"), fragmentShader: [ "uniform sampler2D frameTexture;", "uniform sampler2D tDiffuse;", "uniform float exposure;", "varying vec2 vUv;", "void main() {", "vec4 n = texture2D(frameTexture, vUv);", "vec4 o = texture2D(tDiffuse, vUv);", "vec3 sum = n.rgb + o.rgb;", "gl_FragColor = vec4(mix(o.rgb, sum.rgb, exposure), 1.0);", "}" ].join("\n") </code></pre>
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    1. CO[This discussion](https://github.com/mrdoob/three.js/issues/587) seems to indicate that you should create the WebGLRenderer like so: `new WebGLRenderer({ preserveDrawingBuffer: true })`, and set `renderer.autoClearColor` to false.
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    2. COThat will work for creating effects on geometry (like motion blur), but it has no effect on the actual textures on the geometry. That is what I'm trying to target.
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