Spinning Images in WebGL

Andrei Prikaznov

Jan. 15, 12 · Interview

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today we continue html5 canvas examples. and today is our second tutorial for webgl. we will be creating animated twisting images. also we will add handlers to manipulate the images with mouse and keyboard.

here are our demo and downloadable package:

live demo

download in package

ok, download the example files and lets start coding !

step 1. html

here are html sources of our demo. as you can see – just an empty page.

index.html

<!doctype html>
<html lang="en" >
<head>
    <link href="css/main.css" rel="stylesheet" type="text/css" />
    <script type="text/javascript" src="js/glmatrix-0.9.5.min.js"></script>
    <script type="text/javascript" src="js/webgl-utils.js"></script>
    <script type="text/javascript" src="js/script.js"></script>
    <title>creating a keyboard sensitive 3d twisted images in webgl | script tutorials</title>
</head>
<body onload="initwebgl();">
    <div class="example">
        <h3><a href="http://www.script-tutorials.com/twisting-images-webgl/">creating a keyboard sensitive 3d twisted images in webgl | script tutorials</a></h3>
        <h3>you can use your mouse + arrow keys + page up / down</h3>
        <canvas id="panel" width="500" height="333"></canvas>
        <div style="clear:both;"></div>
    </div>
</body>
</html>

step 2. css

here are used css styles.

css/main.css

body {
    background:#eee;
    font-family:verdana, helvetica, arial, sans-serif;
    margin:0;
    padding:0
}
.example {
    background:#fff;
    width:500px;
    font-size:80%;
    border:1px #000 solid;
    margin:20px auto;
    padding:15px;
    position:relative;
    -moz-border-radius: 3px;
    -webkit-border-radius:3px
}
h3 {
    text-align:center;
}

step 3. js

js/webgl-utils.js and js/glmatrix-0.9.5.min.js

these files we will use in project for working with webgl. both files will in our package.

js/script.js

var gl; // global webgl object
var shaderprogram;

var pics_names=['1.png', '2.png', '3.png', '4.png', '5.png', '6.png', '7.png'];
var pics_num=pics_names.length;

// diffirent initializations

function initgl(canvas) {
    try {
        gl = canvas.getcontext('experimental-webgl');
        gl.viewportwidth = canvas.width;
        gl.viewportheight = canvas.height;
    } catch (e) {}
    if (! gl) {
        alert('can`t initialise webgl, not supported');
    }
}

function getshader(gl, type) {
    var str = '';
    var shader;

    if (type == 'x-fragment') {
        str = "#ifdef gl_es\n"+
"precision highp float;\n"+
"#endif\n"+
"varying vec2 vtexturecoord;\n"+
"uniform sampler2d usampler;\n"+
"void main(void) {\n"+
"    gl_fragcolor = texture2d(usampler, vec2(vtexturecoord.s, vtexturecoord.t));\n"+
"}\n";
        shader = gl.createshader(gl.fragment_shader);
    } else if (type == 'x-vertex') {
        str = "attribute vec3 avertexposition;\n"+
"attribute vec2 atexturecoord;\n"+
"uniform mat4 umvmatrix;\n"+
"uniform mat4 upmatrix;\n"+
"varying vec2 vtexturecoord;\n"+
"void main(void) {\n"+
"    gl_position = upmatrix * umvmatrix * vec4(avertexposition, 1.0);\n"+
"    vtexturecoord = atexturecoord;\n"+
"}\n";
        shader = gl.createshader(gl.vertex_shader);
    } else {
        return null;
    }

    gl.shadersource(shader, str);
    gl.compileshader(shader);

    if (!gl.getshaderparameter(shader, gl.compile_status)) {
        alert(gl.getshaderinfolog(shader));
        return null;
    }
    return shader;
}

function initshaders() {
    var fragmentshader = getshader(gl, 'x-fragment');
    var vertexshader = getshader(gl, 'x-vertex');

    shaderprogram = gl.createprogram();
    gl.attachshader(shaderprogram, vertexshader);
    gl.attachshader(shaderprogram, fragmentshader);
    gl.linkprogram(shaderprogram);

    if (!gl.getprogramparameter(shaderprogram, gl.link_status)) {
        alert('can`t initialise shaders');
    }

    gl.useprogram(shaderprogram);

    shaderprogram.vertexpositionattribute = gl.getattriblocation(shaderprogram, 'avertexposition');
    gl.enablevertexattribarray(shaderprogram.vertexpositionattribute);

    shaderprogram.texturecoordattribute = gl.getattriblocation(shaderprogram, 'atexturecoord');
    gl.enablevertexattribarray(shaderprogram.texturecoordattribute);

    shaderprogram.pmatrixuniform = gl.getuniformlocation(shaderprogram, 'upmatrix');
    shaderprogram.mvmatrixuniform = gl.getuniformlocation(shaderprogram, 'umvmatrix');
    shaderprogram.sampleruniform = gl.getuniformlocation(shaderprogram, 'usampler');
}

var objvertexpositionbuffer=new array();
var objvertextexturecoordbuffer=new array();
var objvertexindexbuffer=new array();

function initobjbuffers() {
    for (var i=0;i<pics_num;i=i+1) {
        objvertexpositionbuffer[i] = gl.createbuffer();
        gl.bindbuffer(gl.array_buffer, objvertexpositionbuffer[i]);
        vertices = [
            math.cos(i*((2*math.pi)/pics_num)), -0.5,  math.sin(i*((2*math.pi)/pics_num)),
            math.cos(i*((2*math.pi)/pics_num)), 0.5,  math.sin(i*((2*math.pi)/pics_num)),
            math.cos((i+1)*((2*math.pi)/pics_num)), 0.5, math.sin((i+1)*((2*math.pi)/pics_num)),
            math.cos((i+1)*((2*math.pi)/pics_num)), -0.5,  math.sin((i+1)*((2*math.pi)/pics_num)),
        ];
        gl.bufferdata(gl.array_buffer, new float32array(vertices), gl.static_draw);
        objvertexpositionbuffer[i].itemsize = 3;
        objvertexpositionbuffer[i].numitems = 4;

        objvertextexturecoordbuffer[i] = gl.createbuffer();
        gl.bindbuffer(gl.array_buffer,  objvertextexturecoordbuffer[i] );
        var texturecoords = [
            0.0, 0.0,
            0.0, 1.0,
            1.0, 1.0,
            1.0, 0.0,
        ];
        gl.bufferdata(gl.array_buffer, new float32array(texturecoords), gl.static_draw);
        objvertextexturecoordbuffer[i].itemsize = 2;
        objvertextexturecoordbuffer[i].numitems = 4;

        objvertexindexbuffer[i] = gl.createbuffer();
        gl.bindbuffer(gl.element_array_buffer, objvertexindexbuffer[i]);
        var objvertexindices = [
            0, 1, 2,
            0, 2, 3,
        ];
        gl.bufferdata(gl.element_array_buffer, new uint16array(objvertexindices), gl.static_draw);
        objvertexindexbuffer[i].itemsize = 1;
        objvertexindexbuffer[i].numitems = 6;
    }
}

function handleloadedtexture(texture) {
    gl.bindtexture(gl.texture_2d, texture);
    gl.pixelstorei(gl.unpack_flip_y_webgl, true);
    gl.teximage2d(gl.texture_2d, 0, gl.rgba, gl.rgba, gl.unsigned_byte, texture.image);
    gl.texparameteri(gl.texture_2d, gl.texture_mag_filter, gl.linear);
    gl.texparameteri(gl.texture_2d, gl.texture_min_filter, gl.linear);
    gl.bindtexture(gl.texture_2d, null);
}

var cratetextures = array();
function inittexture(image) {
    var crateimage = new image();

    var texture = gl.createtexture();
    texture.image = crateimage;
    crateimage.src = image;

    crateimage.onload = function () {
        handleloadedtexture(texture)
    }
    return texture;
}

function inittextures() {
    for (var i=0; i < pics_num; i++) {
        cratetextures[i]=inittexture(pics_names[i]);
    }
}

var mvmatrix = mat4.create();
var mvmatrixstack = [];
var pmatrix = mat4.create();

function setmatrixuniforms() {
    gl.uniformmatrix4fv(shaderprogram.pmatrixuniform, false, pmatrix);
    gl.uniformmatrix4fv(shaderprogram.mvmatrixuniform, false, mvmatrix);
}

function degtorad(degrees) {
    return degrees * math.pi / 180;
}

// mouse and keyboard handlers

var xrot = 0;
var xspeed = 0;
var yrot = 0;
var yspeed = 10;
var z = -3.0;

var currentlypressedkeys = {};
function handlekeydown(event) {
    currentlypressedkeys[event.keycode] = true;
}

function handlekeyup(event) {
    currentlypressedkeys[event.keycode] = false;
}

function handlekeys() {
    if (currentlypressedkeys[33]) { // page up
        z -= 0.05;
    }
    if (currentlypressedkeys[34]) { // page down
        z += 0.05;
    }
    if (currentlypressedkeys[37]) { // left cursor key
        yspeed -= 1;
    }
    if (currentlypressedkeys[39]) { // right cursor key
        yspeed += 1;
    }
    if (currentlypressedkeys[38]) { // up cursor key
        xspeed -= 1;
    }
    if (currentlypressedkeys[40]) { // down cursor key
        xspeed += 1;
    }
}

var mousedown = false;
var lastmousex = null;
var lastmousey = null;

var rotationmatrix = mat4.create();
mat4.identity(rotationmatrix);

function handlemousedown(event) {
    mousedown = true;
    lastmousex = event.clientx;
    lastmousey = event.clienty;
}

function handlemouseup(event) {
    mousedown = false;
}

function handlemousemove(event) {
    if (!mousedown) {
      return;
    }
    var newx = event.clientx;
    var newy = event.clienty;

    var deltax = newx - lastmousex;
    var newrotationmatrix = mat4.create();
    mat4.identity(newrotationmatrix);
    mat4.rotate(newrotationmatrix, degtorad(deltax / 5), [0, 1, 0]);

    var deltay = newy - lastmousey;
    mat4.rotate(newrotationmatrix, degtorad(deltay / 5), [1, 0, 0]);

    mat4.multiply(newrotationmatrix, rotationmatrix, rotationmatrix);

    lastmousex = newx
    lastmousey = newy;
}

// draw scene and initialization

var movematrix = mat4.create();
mat4.identity(movematrix);

function drawscene() {
    gl.viewport(0, 0, gl.viewportwidth, gl.viewportheight);
    gl.clear(gl.color_buffer_bit | gl.depth_buffer_bit);

    mat4.perspective(45, gl.viewportwidth / gl.viewportheight, 0.1, 100.0, pmatrix);

    mat4.identity(mvmatrix);

    mat4.translate(mvmatrix, [0.0, 0.0, z]);

    mat4.rotate(mvmatrix, degtorad(xrot), [1, 0, 0]);
    mat4.rotate(mvmatrix, degtorad(yrot), [0, 1, 0]);

    mat4.multiply(mvmatrix, movematrix);
    mat4.multiply(mvmatrix, rotationmatrix);

    for (var i=0;i<pics_num;i=i+1) {
        gl.bindbuffer(gl.array_buffer, objvertexpositionbuffer[i]);
        gl.vertexattribpointer(shaderprogram.vertexpositionattribute, objvertexpositionbuffer[i].itemsize, gl.float, false, 0, 0);

        gl.bindbuffer(gl.array_buffer, objvertextexturecoordbuffer[i]);
        gl.vertexattribpointer(shaderprogram.texturecoordattribute, objvertextexturecoordbuffer[i].itemsize, gl.float, false, 0, 0);

        gl.activetexture(gl.texture0);
        gl.bindtexture(gl.texture_2d, cratetextures[i]);
        gl.uniform1i(shaderprogram.sampleruniform, 0);

        gl.bindbuffer(gl.element_array_buffer, objvertexindexbuffer[i]);
        setmatrixuniforms();
        gl.drawelements(gl.triangles, objvertexindexbuffer[i].numitems, gl.unsigned_short, 0);
    }
}

var lasttime = 0;
function animate() {
    var timenow = new date().gettime();
    if (lasttime != 0) {
        var elapsed = timenow - lasttime;

        xrot += (xspeed * elapsed) / 1000.0;
        yrot += (yspeed * elapsed) / 1000.0;
    }
    lasttime = timenow;
}

function drawframe() {
    requestanimframe(drawframe);
    handlekeys();
    drawscene();
    animate();
}

function initwebgl() {
    var canvas = document.getelementbyid('panel');
    initgl(canvas);
    initshaders();
    initobjbuffers();
    inittextures();

    gl.clearcolor(1.0, 1.0, 1.0, 1.0);
    gl.enable(gl.depth_test);

    document.onkeydown = handlekeydown;
    document.onkeyup = handlekeyup;

    canvas.onmousedown = handlemousedown;
    document.onmouseup = handlemouseup;
    document.onmousemove = handlemousemove;

    drawframe();
}

and again – long code, but most important. i separated all code to 3 sides: initializations, handlers and drawing of scene. hope that you already read our previos webgl lesson . in this case it will more easy to understand today`s code. just make attention that instead color buffer we will using texture buffer (objvertextexturecoordbuffer). also, this demo able to work with any amouht of used images (better – more than 3).