WebGL (Abstraction) for All

James Milner

@JamesLMilner

loxodrome.io

WebGL?

WebGL is a library for displaying graphics in the browser

It Uses HTML5 Canvas

Why WebGL?

But...

Greg Tavares

"what many people don't [realise] is that WebGL is a rasterization API, not a 3D API"

It's API is also low level

Alongside our WebGL JavaScript API we require shaders

Vertex Shaders, Fragment Shaders

Introducing GLSL ES

Graphics Library Shader Language

<!-- Drawing a green square -->
<script id="2d-vertex-shader" type="x-shader/x-vertex">
    attribute vec2 a_position;
     
    void main() {
      gl_Position = vec4(a_position, 0, 1); // X, Y, Z, W
    }
</script>
 
<script id="2d-fragment-shader" type="x-shader/x-fragment">
    void main() {
      gl_FragColor = vec4(0, 1, 0, 1);  //  Green (RGBA)
    }
</script>

Credit: dev.opera.com

Lets Examine Some Code...

<html>

<head>
<title>Learning WebGL — lesson 1</title>
<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">

<script type="text/javascript" src="glMatrix-0.9.5.min.js"></script>

<script id="shader-fs" type="x-shader/x-fragment">
    precision mediump float;

    void main(void) {
        gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
    }
</script>

<script id="shader-vs" type="x-shader/x-vertex">
    attribute vec3 aVertexPosition;

    uniform mat4 uMVMatrix;
    uniform mat4 uPMatrix;

    void main(void) {
        gl_Position = uPMatrix * uMVMatrix * vec4(aVertexPosition, 1.0);
    }
</script>


<script type="text/javascript">

    var gl;
    function initGL(canvas) {
        try {
            var gl = canvas.getContext("experimental-webgl");
            if (!gl) {
              gl = canvas.getContext("webgl");
            }
            gl.viewportWidth = canvas.width;
            gl.viewportHeight = canvas.height;
        } catch (e) {
        }
        if (!gl) {
            alert("Could not initialise WebGL, sorry :-(");
        }
    }


    function getShader(gl, id) {
        var shaderScript = document.getElementById(id);
        if (!shaderScript) {
            return null; // No shader script with that id
        }

        var str = ""; //concatenate the whole shader together
        var k = shaderScript.firstChild;
        while (k) {
            if (k.nodeType == 3) { //text will have nodeType property will return 3.
                str += k.textContent;
            }
            k = k.nextSibling;
        }

        var shader;
        if (shaderScript.type == "x-shader/x-fragment") {
            shader = gl.createShader(gl.FRAGMENT_SHADER); // if fragment
        } else if (shaderScript.type == "x-shader/x-vertex") {
            shader = gl.createShader(gl.VERTEX_SHADER); // if vertex
        } else {
            return null;
        }

        gl.shaderSource(shader, str); // link type and source
        gl.compileShader(shader); // compile shader 

        if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
            alert(gl.getShaderInfoLog(shader));
            return null;
        }

        return shader;
    }


    var shaderProgram;

    function initShaders() {
        var fragmentShader = getShader(gl, "shader-fs");
        var vertexShader = getShader(gl, "shader-vs");

        shaderProgram = gl.createProgram(); // create shader program
        gl.attachShader(shaderProgram, vertexShader); // add vertex shader
        gl.attachShader(shaderProgram, fragmentShader); // add vertex shader
        gl.linkProgram(shaderProgram); // Link the two to program

        if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
            alert("Could not initialise shaders");
        }

        gl.useProgram(shaderProgram); 

        shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
        gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);

        shaderProgram.pMatrixUniform = gl.getUniformLocation(shaderProgram, "uPMatrix");
        shaderProgram.mvMatrixUniform = gl.getUniformLocation(shaderProgram, "uMVMatrix");
    }


    var mvMatrix = mat4.create(); // glMatrix functions
    var pMatrix = mat4.create();

    function setMatrixUniforms() {
        gl.uniformMatrix4fv(shaderProgram.pMatrixUniform, false, pMatrix);
        gl.uniformMatrix4fv(shaderProgram.mvMatrixUniform, false, mvMatrix);
    }


    var triangleVertexPositionBuffer;
    var squareVertexPositionBuffer;

    function initBuffers() {

        //Triangle
        triangleVertexPositionBuffer = gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER, triangleVertexPositionBuffer);
        var vertices = [
             0.0,  1.0,  0.0,
            -1.0, -1.0,  0.1,
             1.0, -1.0,  0.0
        ];
        gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
        triangleVertexPositionBuffer.itemSize = 3;
        triangleVertexPositionBuffer.numItems = 3;

        //Square
        squareVertexPositionBuffer = gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);
        vertices = [
             1.0,  1.0,  0.0,
            -1.0,  1.0,  0.0,
             1.0, -1.0,  0.0,
            -1.0, -1.0,  0.0
        ];
        gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
        squareVertexPositionBuffer.itemSize = 3;
        squareVertexPositionBuffer.numItems = 4;
    }


    function drawScene() {
        gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
        // Clears the color and depth buffers

        mat4.perspective(45, gl.viewportWidth / gl.viewportHeight, 0.1, 100.0, pMatrix);
        // Field of View = 45 , width-to-height ratio of canvas, min view distance, max view distance
        mat4.identity(mvMatrix);

        mat4.translate(mvMatrix, [-1.5, 0.0, -7.0]);
        gl.bindBuffer(gl.ARRAY_BUFFER, triangleVertexPositionBuffer);
        gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, triangleVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
        setMatrixUniforms();
        gl.drawArrays(gl.TRIANGLES, 0, triangleVertexPositionBuffer.numItems);

        mat4.translate(mvMatrix, [3.0, 0.0, 0.0]);
        gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);
        gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, squareVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
        setMatrixUniforms();
        gl.drawArrays(gl.TRIANGLE_STRIP, 0, squareVertexPositionBuffer.numItems);
    }



    function webGLStart() {
        var canvas = document.getElementById("lesson01-canvas"); //Get Canvas
        initGL(canvas);
        initShaders();
        initBuffers();

        gl.clearColor(0.0, 0.0, 0.0, 1.0); //Black
        gl.enable(gl.DEPTH_TEST);

        drawScene();
    }


</script>


</head>


<body onload="webGLStart();">
    <a href="http://learningwebgl.com/blog/?p=28"><< Back to Lesson 1</a><br />

    <canvas id="lesson01-canvas" style="border: none;" width="500" height="500"></canvas>

    <br/>
    <a href="http://learningwebgl.com/blog/?p=28"><< Back to Lesson 1</a><br />
</body>

</html>

Frameworks will help us move faster

Raw WebGL

TWGL

Three.js

Babylon.js

Scene.js

OSG.js

GLGE

Increasing Abstraction

CopperLicht

PhiloGL

Which is best?

It depends

I like Three.js

WebGL & libraries have great potential & use cases

Here's some examples of places I've ended up using it