CODEWITHSUNDEEP
imagehtmlcanvasdata-uri
Yahoo
Yahoo

Reputation: 4187

Drawing an image from a data URL to a canvas

How can i open an image in a Canvas ? which is encoded

I am using the 

var strDataURI = oCanvas.toDataURL();

The output is the encoded base 64 image. How can i draw this image on a canvas?

I want to use the strDataURI and create the Image ? Is it poosible ?
If its not then what possibly can be the solution for loading the image on a canvas ?

Upvotes: 149

Views: 271270

Answers (7)

joe
joe

Reputation: 5522

In case you don't like the onload callback approach, you can "promisify" it like so:

let url = "data:image/gif;base64,R0lGODl...";
let img = new Image();
await new Promise(r => img.onload=r, img.src=url);
// now do something with img

Upvotes: 13

gabrielrincon
gabrielrincon

Reputation: 896

Mixing the answers I do.

function drawDataURIOnCanvas(strDataURI, canvas) {
   var img = new window.Image();
   img.addEventListener("load", function () {
     canvas.getContext("2d").clearRect(0, 0, canvas.width, canvas.height);
     canvas.width = img.width;
     canvas.height = img.height;
     canvas.getContext("2d").drawImage(img, 0, 0, img.width, img.height);
   });

   img.setAttribute("src", strDataURI);
}

Upvotes: 4

Hitesh Sahu
Hitesh Sahu

Reputation: 45052

You might wanna clear the old Image before setting a new Image.

You also need to update the Canvas size for a new Image.

This is how I am doing in my project:

    // on image load update Canvas Image 
    this.image.onload = () => {

      // Clear Old Image and Reset Bounds
      canvasContext.clearRect(0, 0, this.canvas.width, this.canvas.height);
      this.canvas.height = this.image.height;
      this.canvas.width = this.image.width;

      // Redraw Image
      canvasContext.drawImage(
        this.image,
        0,
        0,
        this.image.width,
        this.image.height
      );
    };

Upvotes: 1

Raphael C
Raphael C

Reputation: 2402

function drawDataURIOnCanvas(strDataURI, canvas) {
    "use strict";
    var img = new window.Image();
    img.addEventListener("load", function () {
        canvas.getContext("2d").drawImage(img, 0, 0);
    });
    img.setAttribute("src", strDataURI);
}

Upvotes: 12

user2672373
user2672373

Reputation:

Perhaps this fiddle would help ThumbGen - jsFiddle It uses File API and Canvas to dynamically generate thumbnails of images.

(function (doc) {
    var oError = null;
    var oFileIn = doc.getElementById('fileIn');
    var oFileReader = new FileReader();
    var oImage = new Image();
    oFileIn.addEventListener('change', function () {
        var oFile = this.files[0];
        var oLogInfo = doc.getElementById('logInfo');
        var rFltr = /^(?:image\/bmp|image\/cis\-cod|image\/gif|image\/ief|image\/jpeg|image\/jpeg|image\/jpeg|image\/pipeg|image\/png|image\/svg\+xml|image\/tiff|image\/x\-cmu\-raster|image\/x\-cmx|image\/x\-icon|image\/x\-portable\-anymap|image\/x\-portable\-bitmap|image\/x\-portable\-graymap|image\/x\-portable\-pixmap|image\/x\-rgb|image\/x\-xbitmap|image\/x\-xpixmap|image\/x\-xwindowdump)$/i
        try {
            if (rFltr.test(oFile.type)) {
                oFileReader.readAsDataURL(oFile);
                oLogInfo.setAttribute('class', 'message info');
                throw 'Preview for ' + oFile.name;
            } else {
                oLogInfo.setAttribute('class', 'message error');
                throw oFile.name + ' is not a valid image';
            }
        } catch (err) {
            if (oError) {
                oLogInfo.removeChild(oError);
                oError = null;
                $('#logInfo').fadeOut();
                $('#imgThumb').fadeOut();
            }
            oError = doc.createTextNode(err);
            oLogInfo.appendChild(oError);
            $('#logInfo').fadeIn();
        }
    }, false);
    oFileReader.addEventListener('load', function (e) {
        oImage.src = e.target.result;
    }, false);
    oImage.addEventListener('load', function () {
        if (oCanvas) {
            oCanvas = null;
            oContext = null;
            $('#imgThumb').fadeOut();
        }
        var oCanvas = doc.getElementById('imgThumb');
        var oContext = oCanvas.getContext('2d');
        var nWidth = (this.width > 500) ? this.width / 4 : this.width;
        var nHeight = (this.height > 500) ? this.height / 4 : this.height;
        oCanvas.setAttribute('width', nWidth);
        oCanvas.setAttribute('height', nHeight);
        oContext.drawImage(this, 0, 0, nWidth, nHeight);
        $('#imgThumb').fadeIn();
    }, false);
})(document);

Upvotes: 4

Phrogz
Phrogz

Reputation: 303136

Given a data URL, you can create an image (either on the page or purely in JS) by setting the src of the image to your data URL. For example:

var img = new Image;
img.src = strDataURI;

The drawImage() method of HTML5 Canvas Context lets you copy all or a portion of an image (or canvas, or video) onto a canvas.

You might use it like so:

var myCanvas = document.getElementById('my_canvas_id');
var ctx = myCanvas.getContext('2d');
var img = new Image;
img.onload = function(){
  ctx.drawImage(img,0,0); // Or at whatever offset you like
};
img.src = strDataURI;

Edit: I previously suggested in this space that it might not be necessary to use the onload handler when a data URI is involved. Based on experimental tests from this question, it is not safe to do so. The above sequence—create the image, set the onload to use the new image, and then set the src—is necessary for some browsers to surely use the results.

Upvotes: 241

user475434
user475434

Reputation: 316

in javascript , using jquery for canvas id selection :

 var Canvas2 = $("#canvas2")[0];
        var Context2 = Canvas2.getContext("2d");
        var image = new Image();
        image.src = "images/eye.jpg";
        Context2.drawImage(image, 0, 0);

html5:

<canvas id="canvas2"></canvas>

Upvotes: -6

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