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HTML5 Canvas 3D Sphere

04.18.2012
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Our new tutorial tells us how to create an animated 3D Sphere (through direct access to pixels on the canvas). The sphere itself moves around the canvas continuously. This example should work in  most modern browsers (like Firefox, Chrome, Safari and even in IE).

In the end, you should to get something like this:

HTML5 Canvas 3D Sphere

Here are our demo and downloadable package:

Live Demo

download in package

Ok, download the source files and let's start coding !

Step 1. HTML

This is the markup of our page.

index.html
<div class="container">
    <canvas id="slideshow" width="1024" height="631"></canvas>
    <canvas id="obj" width="256" height="256"></canvas>
</div>

I prepared 2 canvas objects here: the first for the source image, and the second one for our Sphere.

Step 2. CSS

css/main.css
.container {
    height: 631px;
    margin: 50px auto;
    position: relative;
    width: 1024px;
    z-index: 1;
}
#obj {
    position: absolute;
    z-index: 2;
}

We should put our Sphere object above our main canvas.

Step 3. JS

js/script.js
var canvas, ctx;
var canvasObj, ctxObj;
var iDstW = 256;
var iDstH = 256;
var iXSpeed = 4;
var iYSpeed = 3;
var iLastX = iDstW / 2;
var iLastY = iDstH / 2;
var oImage;
var aMap = [];
var aBitmap;

var mathSphere = function(px, py) {
    var x = px - iDstW / 2;
    var y = py - iDstH / 2;
    var r = Math.sqrt(x * x + y * y);
    var maxR = iDstW / 2;
    if (r > maxR) return {'x':px, 'y':py};

    var a = Math.atan2(y, x);
    var k = (r / maxR) * (r / maxR) * 0.5 + 0.5;
    var dx = Math.cos(a) * r * k;
    var dy = Math.sin(a) * r * k;
    return {'x': dx + iDstW / 2, 'y': dy + iDstH / 2};
}

window.onload = function(){

    // load background
    oImage = new Image();
    oImage.src="images/bg.jpg";
    oImage.onload = function () {

        // creating canvas and context objects
        canvas = document.getElementById('slideshow');
        ctx = canvas.getContext('2d');
        canvasObj = document.getElementById('obj');
        ctxObj = canvasObj.getContext('2d');

        // clear context
        ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);

        // and draw source image
        ctx.drawImage(oImage, 0, 0);

        aBitmap = ctx.getImageData(0, 0, iDstW, iDstH);
        for (var y = 0; y < iDstH; y++) {
            for (var x = 0; x < iDstW; x++) {
                var t = mathSphere(x, y);
                aMap[(x + y * iDstH) * 2 + 0] = Math.max(Math.min(t.x, iDstW - 1), 0);
                aMap[(x + y * iDstH) * 2 + 1] = Math.max(Math.min(t.y, iDstH - 1), 0);
            }
        }

        // begin updating scene
        updateScene();
    };

    function updateScene() {

        // update last coordinates
        iLastX = iLastX + iXSpeed;
        iLastY = iLastY + iYSpeed;

        // reverse speed
        if (iLastX > ctx.canvas.width - iDstW/2) {
            iXSpeed = -3;
        }
        if (iLastX < iDstW/2) {
            iXSpeed = 3;
        }
        if (iLastY > ctx.canvas.height - iDstH/2) {
            iYSpeed = -3;
        }
        if (iLastY < iDstH/2) {
            iYSpeed = 3;
        }

        // shifting of the second object
        canvasObj.style.left = iLastX - Math.floor(iDstW / 2) + 'px';
        canvasObj.style.top = iLastY - (Math.floor(iDstH / 2)) + 'px';

        // draw result Sphere
        var aData = ctx.getImageData(iLastX - Math.ceil(iDstW / 2), iLastY - Math.ceil(iDstH / 2), iDstW, iDstH + 1);
        for (var j = 0; j < iDstH; j++) {
            for (var i = 0; i < iDstW; i++) {
                var u = aMap[(i + j * iDstH) * 2];
                var v = aMap[(i + j * iDstH) * 2 + 1];
                var x = Math.floor(u);
                var y = Math.floor(v);
                var kx = u - x;
                var ky = v - y;
                for (var c = 0; c < 4; c++) {
                    aBitmap.data[(i + j * iDstH) * 4 + c] =
                      (aData.data[(x + y * iDstH) * 4 + c] * (1 - kx) + aData.data[((x + 1) + y * iDstH) * 4 + c] * kx) * (1-ky) +
                      (aData.data[(x + (y + 1) * iDstH) * 4 + c] * (1 - kx) + aData.data[((x + 1) + (y + 1) * iDstH) * 4 + c] * kx) * (ky);
                }
            }
        }
        ctxObj.putImageData(aBitmap,0,0);

        // update timer
        setTimeout(updateScene, 16);
    }
};

During initialization, the script prepares two canvas objects and two contexts. Then, it loads our main background image, and draws it as our first context. Then it prepares a hash table of sphere transformations: aMap. And, in the end – it starts the timer, which updates the main scene. In this function (updateScene) we update the coordinates of our Sphere object, and draw the updated sphere at our second location.

Live Demo

download in package

Conclusion

I hope that today’s 3D HTML5 Sphere lesson has been interesting for you. We have done another  nice html5 example. I will be glad to see your thanks and comments. Good luck!

Published at DZone with permission of Andrey Prikaznov, author and DZone MVB. (source)

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