javascript - Tainted canvas error thrown when refreshing the page with F5 -


i have problem code, quite similar codepen. 

var img = new image();  img.src = 'https://upload.wikimedia.org/wikipedia/commons/thumb/6/63/diceros_bicornis.jpg/320px-diceros_bicornis.jpg';  img.crossorigin = "anonymous"  var canvas = document.getelementbyid('canvas');  var ctx = canvas.getcontext('2d');  img.onload = function() {    ctx.drawimage(img, 0, 0);    img.style.display = 'none';  };  var color = document.getelementbyid('color');  function pick(event) {    var x = event.layerx;    var y = event.layery;    var pixel = ctx.getimagedata(x, y, 1, 1);    var data = pixel.data;    var rgba = 'rgba(' + data[0] + ', ' + data[1] +               ', ' + data[2] + ', ' + (data[3] / 255) + ')';    color.style.background =  rgba;    color.textcontent = rgba;  }  canvas.addeventlistener('mousemove', pick);
<!-- learn code on mdn: https://developer.mozilla.org/en-us/docs/web/api/canvas_api/tutorial/pixel_manipulation_with_canvas -->    <canvas id="canvas" width="300" height="227" style="float:left"></canvas>  <div id="color" style="width:200px;height:50px;float:left"></div>

it somehow works when page first open. when refresh page f5, sometimes starts throwing tainted canvas error. when click x close tab, , click link again open brand new tab work again.

i have img.crossorigin = "anonymous".

that sounds chrome bug, workaround-able : set crossorigin attribute first.

the first time request made, crossorigin attribute set before image has loaded, hence browser redo request.

but when reload page, image cached, , loads before crossorigin attribute set. canvas tainted.

for similar little bugs cases, should define onload event handler before setting src attribute :

var canvas = document.getelementbyid('canvas');  var ctx = canvas.getcontext('2d');    var img = new image();  img.crossorigin = "anonymous"  img.onload = function() {    ctx.drawimage(img, 0, 0);    img.style.display = 'none';  };  // set src last  img.src = 'https://upload.wikimedia.org/wikipedia/commons/thumb/6/63/diceros_bicornis.jpg/320px-diceros_bicornis.jpg';    var color = document.getelementbyid('color');  function pick(event) {    var x = event.layerx;    var y = event.layery;    var pixel = ctx.getimagedata(x, y, 1, 1);    var data = pixel.data;    var rgba = 'rgba(' + data[0] + ', ' + data[1] +               ', ' + data[2] + ', ' + (data[3] / 255) + ')';    color.style.background =  rgba;    color.textcontent = rgba;  }  canvas.addeventlistener('mousemove', pick);
<!-- learn code on mdn: https://developer.mozilla.org/en-us/docs/web/api/canvas_api/tutorial/pixel_manipulation_with_canvas -->    <canvas id="canvas" width="300" height="227" style="float:left"></canvas>  <div id="color" style="width:200px;height:50px;float:left"></div>


Comments

Post a Comment

Popular posts from this blog

ios - Change Storyboard View using Seague -

i have following code checks connection server, , depending on want change views if no connection found. nsstring *connect = [nsstring stringwithcontentsofurl:[nsurl urlwithstring:@"http://myserver.com"] encoding:nsutf8stringencoding error:nil]; if (connect == null) { [self performseguewithidentifier:@"network_failure" sender:self]; } else { // other code here } my problem not change views. have added storyboard segue between 2 views identifier of network_failure . not have navigation controller or that, problem? thanks help! no not problem. first of all, in objectivec exists nil object oriented null . must use that. so: if(connect == nil) or better: if(!connect) so due fact nil not same of null , probably code does't enter in if scope . you have been able discover breakpoint. anyway: be sure set trigger segue (line) 2 view controller , , name network_failure (that not best name. should instead view1toview2 ) as, m...
Read more

commonjs - How to write a typescript definition file for a node module that exports a function? -

consider, toml node module can use: // toml.d.ts declare module toml { export function parse(value:string):any; } declare module "toml" { export = toml; } then: /// <reference path="../../../../../defs/toml/toml.d.ts"/> import toml = require('toml'); toml.parse(...); however, node module export single function, such 'glob' ( https://github.com/isaacs/node-glob ). the node usage of module be: var glob = require("glob") glob("*.js", {}, callback(err, files) { ... }); you'd naively expect this: // glob.d.ts declare function globs(paths:string, options:any, callback:{(err:any, files:string[]):void; ...but because typescripts 'import' semantics bit strange, seems can use 'import .. = require()' statement alias modules . trying call: /// <reference path="../../../../../defs/glob/glob.d.ts"/> import blog = require('glob'); results in: error ts2072: mod...
Read more

openid - Okta: Failed to get authorization code through API call -

i'm integrating okta own idp server using okta's api. i'm implementing authorization code flow following steps below: in own server, use /api/v1/authn endpoint sessiontoken. use sessiontoken obtain authorization calling endpoint: /oauth2/v1/authorize?client_id=" + clientid + "&sessiontoken=" + sessiontoken + "&response_type=code&response_mode=query&scope=openid&redirect_uri=" + redirecturl + "&state=evanyang&nonce=" it's supposed return response status code 302 , location header containing redirect url code value. however, keep getting response status code 200 , without location header, html body saying "you using unsupported browser." , "javascript disabled on browser." according api documentation: http://developer.okta.com/docs/api/resources/oidc.html#authentication-request , sessiontoken parameter sufficient this: an okta one-time sessiontoken. allows api-based ...
Read more