HTML5 Canvas Twirl Sphere
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Join For Freein the end, you should get something like this:
here are our demo and downloadable package:
live demo
download in package
ok, please download our 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="630"></canvas> <canvas id="obj" width="256" height="256"></canvas> </div>
i prepared two canvas objects: the first for the resource image, and the second – for our twirl sphere.
step 2. css
css/main.css
.container { height: 630px; margin: 50px auto; position: relative; width: 1024px; z-index: 1; } #obj { position: absolute; z-index: 2; }
we should keep our sphere object above our main canvas.
step 3. js
and now, our main js script file:
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 amapt = []; var abitmap; var mathtwirl = 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, 't': 1}; var a = math.atan2(y, x); a -= 1 - r / maxr; var dx = math.cos(a) * r; var dy = math.sin(a) * r; return {'x': dx+idstw/2, 'y': dy+idsth/2, 't': 1.5} } 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 = mathtwirl(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); amapt[(x + y * idsth)] = t.t; } } // begin updating scene updatescene(); }; function updatescene() { // update last coordinates ilastx = ilastx + ixspeed; ilasty = ilasty + iyspeed; // reverse speed if (ilastx + 1 > ctx.canvas.width - idstw/2) { ixspeed = -4; } if (ilastx - 1 < idstw/2) { ixspeed = 4; } if (ilasty + 1 > ctx.canvas.height - idsth/2) { iyspeed = -3; } if (ilasty - 1 < 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 twirl 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 t = amapt[(i + j * idsth)]; var x = math.floor(u); var y = math.floor(v); var kx = u - x; var ky = v - y; for (var c = 0; c < 3; 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) * t + (adata.data[(x + (y + 1) * idsth) * 4 + c] * (1 - kx) + adata.data[((x + 1) + (y + 1) * idsth) * 4 + c] * kx) * (ky) * t; } } } ctxobj.putimagedata(abitmap,0,0); // update timer settimeout(updatescene, 16); } };
during initialization, the script prepares two canvas objects and two contexts. after initialization, it loads the background image, and drasw it at our first context. then it prepares a hash table for sphere transformations: amap (using the new mathtwirl function). and, finally – it starts the timer that updates the main scene. this function (updatescene) updates the coordinates of our sphere object, and draws the updated sphere at our second context.
live demo
download in package
conclusion
i hope that today’s twirl html5 sphere lesson has been interesting for you. we have finished another nice html5 example. i will be glad to see your thanks and comments. good luck!
Published at DZone with permission of Andrey Prikaznov, DZone MVB. See the original article here.
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