Category Archives: 3D

Intro to Pixel Shaders in Three.js


I recently started playing with shaders in three.js and I wanted to share some of what I’ve discovered so far. Shaders are the ‘secret sauce’ of modern graphics programming and understanding them gives you a lot of extra graphical fire-power.

For me the big obstacle to learning shaders was the lack of documentation or simple examples, so hopefully this post will be useful to others starting out. This post will focus on using pixel shaders to add post-processing effects to Three.js scenes. This post assumes you already know the basics of using Three.js.

What is a Shader?

A Shader is a piece of code that runs directly on the GPU. Most modern devices have powerful GPUs designed to handle graphics effects without taxing the CPU. This means you get a lot of graphical power essentially for free.

The big conceptual shift when considering shaders is that they run in parallel. Instead of looping sequentially through each pixel one-by-one, shaders are applied to each pixel simultaneously, thus taking advantage of the parallel architecture of the GPU.

There are 2 main types of shaders – vertex shaders and pixel shaders.

  • Vertex Shaders generate or modify 3D geometry by manipulating its vertices. A good example is this fireball where the vertex positions of a sphere geometry are deformed by perlin noise.
  • Pixel Shaders (or ‘Fragment Shaders’) modify or draw the pixels in a scene. They are used to render a 3D scene into pixels (rasterization), and also typically used to add lighting and other effects to a 3D scene.

There are 2 different kinds of pixel shaders -

  • Shaders that draw an image or texture directly. These allows you to draw the kind of  abstract patterns seen on These types of shaders can be loaded into a THREE.ShaderMaterial to give cool textures to 3D objects like this example.
  • Shaders that modify another image or texture. These allow you to do post-processing on an existing texture, for example to add a glow or blur to a 3D scene. This second type of shader is what we will be talking about for the remainder of this post.

Pixel Shaders in Three.js

Three.js has an effects manager called EffectsComposer and many useful shaders built in. This code is not compiled into the main Three.js file, rather it is maintained separately in 2 folders in the three.js root folder:

  • /examples/js/postprocessing - contains the main EffectsComposer() class, and a number of ShaderPasses.
  • /examples/js/shaders – contains multiple individual shaders.

Unfortunately these shaders are not very well documented, so you need to dig in and test them out yourself.

Preview some of the three.js built-in shaders with this demo.


Applying Shaders in Three.js

Applying a shader is pretty straight-forward. This example applies a dot screen and RGB shift effect to a simple 3D scene:

To use shaders that come with three.js, first we need to include the required shader JS files. Then in the scene initialization we set up the effect chain:

// postprocessing
composer = new THREE.EffectComposer( renderer );
composer.addPass( new THREE.RenderPass( scene, camera ) );

var dotScreenEffect = new THREE.ShaderPass( THREE.DotScreenShader );
dotScreenEffect.uniforms[ 'scale' ].value = 4;
composer.addPass( dotScreenEffect );

var rgbEffect = new THREE.ShaderPass( THREE.RGBShiftShader );
rgbEffect.uniforms[ 'amount' ].value = 0.0015;
rgbEffect.renderToScreen = true;
composer.addPass( rgbEffect );

First we create an EffectComposer() instance. The effect composer is used to chain together multiple shader passes by calling addPass(). Each Shader Pass applies a different effect to the scene. Order is important as each pass effects the output of the pass before. The first pass is typically the RenderPass(), which renders the 3D scene into the effect chain.

To create a shader pass we either create a ShaderPass() passing in a shader from the ‘shaders’ folder, or we can use some of the pre-built passes from the ‘postprocessing’ folder, such as BloomPass. Each Shader has a number of uniforms which are the input parameters to the shader and define the appearance of the pass. A uniform can be updated every frame, however it remains uniform across all the pixels in the pass. Browse which uniforms are available by viewing the shader JS file.

The last pass in the composer chain needs to be set to to renderToScreen. Then in the render loop, instead of calling renderer.render() you call composer.render()

That’s all you need to apply existing effects. If you want to build your own effects, continue.

GLSL Syntax

WebGL shaders are written in GLSL. The best intro to GLSL syntax I found is at Toby Schachman’s Pixel Shaders interactive tutorial. Go thru this quick tutorial first and you should get a lightbulb appearing over your head. Next take a look at the examples in his example gallery. You can live edit the code to see changes.

GLSL is written in C so get out your ‘Kernighan and Ritchie’ :). Luckily a little code goes a long way so you won’t need to write anything too verbose. The main WebGL language docs are the GLSL ES Reference Pages, which lists all the available functions.  GLSL Data Types are described here. Usually Googling ‘GLSL’ and your query will give you good results.

Some GLSL Notes:

  • Floats always need a number after the decimal point so 1 is written as 1.0
  • GLSL has many useful utility functions built in such as mix() for linear interpolation and clamp() to constrain a value.
  • GLSL allows access to components of vectors using the letters x,y,z,w and r,g,b,a. So for a 2D coordinate vec2 you can use pos.x, pos.y. For a vec4 color you can use col.r, col.g,col.b,col.a
  • Most GLSL functions can handle with multiple input types e.g. float, vec2, vec3 and vec4.
  • Debugging GLSL is notoriously difficult, however Chrome’s JS console will provide pretty good error messaging and will indicate which line of the shader is causing a problem.

Brightness Shader Example

For the first example we will walk through a super simple brightness shader. Slide the slider to change the brightness of the 3D scene.

Shader code can be included in the main JS file or maintained in separate JS files. In this case the shader code is in it’s own file. We can break apart the shader code into 3 sections, the uniforms, the vertex shader and the fragment shader. For this example we can skip the vertex shader since this section remains unchanged for pixel shaders. Three.js shaders require a vertex and fragment shader even if you are only modifying one.

The “uniforms” section lists all the inputs from the main JS. Uniforms can change every frame, but remain the same between all processed pixels

uniforms: {
"tDiffuse": { type: "t", value: null },
"amount": { type: "f", value: 0.5 }
  • tDiffuse is the texture from the previous shader. This name is always the same for three.js shaders. Type ‘t’ is a texture – essentially a 2D bitmap. tDiffuse is always passed in from the previous shader in the effect chain.
  • amount is a custom uniform defined for this shader. Passed in from the main JS. Type ‘f’ is a float.

The fragmentShader (pixel shader) is where the actual pixel processing occurs. First we define the variables, then we define the main() code loop.

fragmentShader: [

"uniform sampler2D tDiffuse;",
"uniform float amount;",
"varying vec2 vUv;",

"void main() {",
"vec4 color = texture2D(tDiffuse, vUv);",
"gl_FragColor = color*amount;",


Here you will notice one of the quirks of shaders in three.js. The shader code is written as a list of strings that are concatenated. This due to the fact that there is no agreed way to load and parse separate GLSL files. It’s not great but you get used to it pretty quick.

  • uniform variables are passed in from main JS. The uniforms listed here must match the uniforms in the uniforms section at the top of the file.
  • varying variables vary for each pixel that is processed. vUv is a 2D vector that contains the UV coordinates of the pixel being processed. UV coords go from 0 to 1. This value is always called vUv and is passed in automatically by three.js

The main() function is the code that runs on each pixel.

  • Line 8 gets the color of this pixel from the passed in texture (tDiffuse) and the coord of this pixel (vUv). vec4 colors are in RGBA format with values from 0 to 1, so (1.0,0.0,0.0,0.5) would be red at 50% opacity.
  • Line 9 sets the gl_FragColor. gl_FragColor is always the output of a pixel shader. This is where you define the color of each output pixel. In this case we simply multiply the actual pixel color by the amount to create a simple brightness effect.

Mirror Shader Example

In addition to modifying the colors of each pixel, you can also copy pixels from one area to another. As in this example Mirror Shader.

For example to copy the left hand side of the screen to the right you can do this:

"uniform sampler2D tDiffuse;",
"varying vec2 vUv;",

"void main() {",
"vec2 p = vUv;",
"if (p.x > 0.5) p.x = 1.0 - p.x;",
"vec4 color = texture2D(tDiffuse, p);",
"gl_FragColor = color;",

This code checks the x position of each pixel it is run on (p.x). If it’s greater than 0.5 then the pixel is on the right hand side of the screen. In this case, instead of getting the gl_FragColor in the normal way, it gets the pixel color of the pixel at position 1.0 – p.x which is the opposite side of the screen.

More Shaders!

Here’s some examples of some more advanced shaders that I built recently. View the source to see how they work.


Simulates a bad TV via horizontal distortion and vertical roll, using Ashima WebGL Noise. Click to randomize uniforms.



Renders a texture as a grid of dots. The demo then applies a glow pass by blurring and compositing the scene via an Additive Blend Shader.



An audio reactive animation. Post-processing via a combination of mirror, dotscreen shader and RGB shift shaders:


Of course this is just scratching the surface of what you can do with shaders, but hopefully it will be enough to get some people started. If you made it this far, congratulations! Let me know how you get on in the comments.

WebCamMesh Demo

See my Experiment on
WebCamMesh is a HTML5 demo that projects webcam video onto a WebGL 3D Mesh. It creates a ‘fake’ 3D depth map by mapping pixel brightness to mesh vertex Z positions. Perlin noise is used to create the ripple effect by modifying the Z positions based on a 2D noise field. CSS3 filters are used to add contrast and saturation effects.

Running the Demo

Use mouse move to tilt and scroll wheel to zoom. The 3D effect works better if the foreground elements are brighter than the background, so try it in a dark room. Run the demo.

The demo requires a WebGL capable machine and WebCam support. Currently that means Chrome and Opera. On my MacBook Pro I get about 30 FPS with Chrome. If the demo craps out, try resizing your browser down and reloading the page.

[UPDATE] - I added Opera support to the demo. Note that Opera does not support CSS filters so you won’t get the contrast and saturation effects. You may also need to enable WebGL for Opera.

Built With:

To Do:

  • Add Audio reactivity to the mesh from MP3 Web audio API
  • Add Snap shot button. Problem is there is no way to save out the pixels with the CSS filters applied, so I need to re-do the filters with shaders.
  • Add grid resolution slider

Generated Images

Loop Waveform Visualizer

See my Experiment on
Chrome’s new Web Audio API allows us to do some pretty amazing audio stuff directly in the browser. Specifically the RealtimeAnalyserNode Interface provides real-time frequency and time-domain audio analysis which allows you to display ‘graphic equalizer’ style level bar charts and waveforms of an audio source. Chrome’s drag-and-drop file handling also allows you to drag and play MP3 files from the desktop. This gives a lot of potential to build very cool realtime audio visualizations in the browser, which was previously only possible using Processing or similar.

The Loop Waveform Visualizer uses a combination of level and waveform data to produce a circular audio visualization of any MP3. Use the mouse to tilt and the mousewheel to zoom.

To run this, you need a WebGL capable machine and the latest Chrome. Also be aware that it won’t look as good when running under Windows, since Chrome’s WebGL implementation on Windows does not suport line thickness (among other issues). It works better if you use a track that has a high dynamic range (meaning the volume of the track changes a lot over time).

The current time slice is rendered in the center, then displaced outwards over time. The level determines the brightness, thickness and Z scale of the loops. The Z displacement gives a nice ‘bounce to the beat’ effect. The waveform shape is drawn into the loop which means you can almost ‘see’ the sound. As with most visualizations, there was a lot of parameter tweaking to give a nice feel. I’m very happy with the performance of this piece – on my box it’s stays pretty solid at 60FPS. This is partially due to the fact that no new 3D objects are created over time. The 160 loops are created on initialization, then have their geometry modified each frame.

I have some plans to improve this piece, including adding post-processing effects, volume sensitivity controls, auto camera movement etc. Let me know if you have any more suggestions for improvement in the comments.

Creative Commons audio sample is from “Screw Base” by Beytah. Built with Three.js. Source is accessible from the demo URL.

Los Angeles WebGL Meetup Recap

The first Los Angeles WebGL Meetup was a big success! Thanks to everyone who showed up.

The purpose of this meetup is to discuss interactive 3D graphics in the browser, using WebGL, Stage3D and even Unity3D. Bartek Drozdz and I put the meetup together so that we can all learn from each other and make some good connections. These technologies came out very recently and there is a lot of potential to make some very cool stuff.

For the first meetup, I gave a presentation on the current state of interactive web 3D. View the demos here. View the slides from the talk here (PDF).

Bartek gave a presentation on his J3D WebGL 3D engine. View the slides from the talk here (PDF).

We plan on doing the next meetup sometime in January. If you are in the area and want to learn about next-generation 3D in the browser, or give a presentation – please join us.

Stage3D vs WebGL Performance

So you want to build some crazy next-gen 3D graphics in the browser? Right now there are 2 good options available: Flash 11′s Stage3D versus JavaScript’s native WebGL.

Demos and Source Code

To compare the performance of both options I built a couple of simple demos that show 100 semi-transparent cubes with Additive Blending and 2 point lights.The purpose of these demos is to compare 2 equivalent 3D scenes built with the 2 technologies.

If you are getting low frame rates, try reducing the size of the browser window. On the Stage3D demo, check the debug panel DRIV field for if it says “OpenGL” or “Software” (see below for what this means).

Building the Demos

For these demos I used Away3D 4 for Stage3D and Three.js for WebGL.

Away3D 4 is the latest version of the popular Flash 3D engine, built to utilize Stage3D. Away3D has a great online community and a well maintained set of API docs. Away3D 4 is currently in alpha and some features are missing, for example there is no Particle System object and the filters/shaders support is pretty limited. Use this tutorial to get started with Away3D 4.

Three.js is an open source WebGL 3D engine that has an energetic community who are constantly adding new features. There are plenty of tutorials showing how to get started with Three.js.

Code Comparison

Away3D and Three.js have very similar logical models and syntax. For example to create a Cube in Away3D, you do this:

var cube:Cube = new Cube(material, 100,100,100); 

To do the same in Three.js, you do this:

var geometry = new THREE.CubeGeometry(100, 100, 100); 
var cube = new THREE.Mesh(geometry, material); 

Supported Platforms

To run with hardware acceleration, Stage3D requires Flash 11 and a recent graphics card. If Stage3D cannot use hardware rendering it will fall back to software rendering which is around 5-10 times slower. For a list of Stage3D unsupported GPUs, check here. You can manually detect for software rendering mode, and handle it appropriately. Stage3D uses OpenGL on Mac and DirectX on Windows. The big advantage for Stage3D is that it will run in IE.

WebGL requires no plugins and is currently supported in Chrome, Firefox, Safari and Opera. (But not IE – cheers Microsoft!). WebGL in Chrome on Windows uses ANGLE which converts WebGL to DirectX and gives good performance.

On the Mac, both Stage3D and WebGL translate to OpenGL, so there is not much difference in performance. Neither options currently run on mobile devices (iOS / Android), however both are expected to in the future.

Performance Comparison

I tested the 2 demos on a MacBook Pro (with an NVIDIA GeForce GT 330M) and a mid-range Windows 7 Dell laptop (with integrated Intel(R) HD Graphics). Your mileage will vary.

Stage3D WebGL
Mac / Chrome 60 FPS (OpenGL) 60 FPS
Mac / Firefox 60 FPS (OpenGL) 60 FPS
Mac / Safari 60 FPS (OpenGL) 60 FPS
Windows / Chrome 8 FPS (Software) 50 FPS
Windows / Firefox 8 FPS (Software) Does not run
Windows / IE 12 FPS (Software) Does not run

On the Mac, Stage3D and WebGL both perform well. On Windows, Stage3D performs well if you have supported hardware, otherwise poorly. On Windows, WebGL performs well in Chrome, otherwise it does not run. It’s interesting that Windows / Chrome with WebGL gives good performance even with an integrated GPU.

On the Mac, the Stage3D demo is slower to initialize and the frame-rate has more stutters than the WebGL equivalent. Stage3D gives more interesting color blending and specular highlights.


Stage3D and WebGL are both great technologies for delivering interactive 3D content in the browser. Away3D and Three.js provide surprisingly similar APIs for developing 3D content.

When the hardware supports it, both options give great performance. Unfortunately neither option runs well across the most common hardware configurations. If you want to target the general population, you will need to provide alternative content for non-supported machines.

Stage3D’s software mode is a nice idea, in that it will show 3D content on unsupported machines. The problem is that the performance is unusably slow. Is it better to show something that performs badly, or to redirect to alternative content?

Since Chrome is a free install on Mac and Windows, you could argue that using WebGL gives a broader reach with decent performance. Perhaps we will start seeing more ‘View this site in Chrome’ banners?

Want more stuff like this? Follow me on Twitter.

UPDATE – There are many comments reporting 60FPS with Windows/Stage3D. The numbers above do not claim to represent a broad range of machine configurations, just what I observed on the 2 machines closest to me. My test PC laptop has an integrated GPU and therefore does not support Stage3D hardware mode. It is a mid-range laptop, less than 6 months old and as such is probably a good indication of where the general public is at.

UPDATE 2 – I’ve updated the demos to allow you to add more cubes, so please go crazy with 1000s of cubes! I also added a mouse look and updated Three.js to r46. On my MBP, WebGL handles 1000 cubes a lot better than Stage3D.


See my Experiment on Rutt-Etra-Izer is a WebGL emulation of the classic Rutt-Etra video synthesizer. This demo replicates the Z-displacement, scanned-line look of the original, but does not attempt to replicate it’s full feature set.

The demo allows you to drag and drop your own images, manipulate them and save the output. Images are generated by scanning the pixels of the input image from top to bottom, with scan-line separated by the ‘Line Separation’ amount. For each line generated, the z-position of the vertices is dependent on the brightness of the pixels.

View Demo | Download Source

Running the Demo

To run the demo you need the latest version of Chrome or Firefox, and a fairly new machine. Check if your browser supports WebGL here. If it’s still not working, try restarting your browser.

If you are experiencing slow performance, there are a few things to try: 

  • Reduce stage size
  • Increase line separation
  • Reduce input image size

Generated Output

You can view more images generated by this demo in this Flickr set.

I also built an audio-reactive version with Processing . View a video of this in action below:

VAC / Rutt-Etra-Izer™ from felixturner on Vimeo.

More About Rutt-Etra

The Rutt-Etra video synthesizer was built by Steve Rutt and Bill Etra in 1972. It was one of the first devices to allow real-time manipulation of live video and helped instigate the video art movement of the 1970s. Unfortunately Steve Rutt recently passed away. His pioneering contributions to the field of video art will be always be remembered.

Anton Marini (Vade) created a fantastic Rutt-Etra Emulator for Quartz Composer. The source code of this demo is inspired by Andy Best’s 3D Web Cam Lines processing experiment.


UPDATE (June 13): It appears that saving images from WebGL is broken in Chrome 12. I’m looking into possible solutions. In the meantime, you can use Firefox instead.

UPDATE (June 14): Saving images in now fixed in Chrome 12. The solution is to call a render() immediately before calling toDataURL(). Thanks again to AlteredQualia and Mr.doob.