Develop Reference

Canvas to PNG on Client Side

I have a canvas and I want to convert it and show in a tag. I know we can convert canvas to image by using toDataURL() and toBlob() but both method give me base64 data which is not a image.
$("#upload_feedback_btn").on("click", function() {
let feedbackSrc = document.getElementById("capture").toDataURL('image/png', 1.0);
$("#feedback_canvas_image").append("<img id='upload_canvas_img' src="+feedbackSrc+">");
});

var can = document.getElementById('canvas1');
var ctx = can.getContext('2d');
ctx.fillRect(50,50,50,50);
var img = new Image();
img.src = can.toDataURL();
document.body.appendChild(img);
http://jsfiddle.net/simonsarris/vgmFN/

Use this, pure javascript:
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d');
make_base();
function make_base()
{
base_image = new Image();
base_image.src = 'img/base.png';
base_image.onload = function(){
context.drawImage(base_image, 100, 100);
}
}

JavaScript Write Text To Image

I Have a issue about write text to image. I need loop the image. But i get some issue. When i do it , Last image showing and the images size is small. Do anyone help me ?
var div=document.getElementById("locations");
var canvas;
window.onload = function(){
for(var i=0;i<10;i++){
canvas=document.createElement("canvas");
canvas.style.width="75px";
canvas.style.height="75px"
var context = canvas.getContext("2d");
var imageObj = new Image();
imageObj.onload = function(){
context.drawImage(imageObj, 0, 0);
context.font = "17px Calibri";
context.fillText(i, 30, 36);
};
imageObj.src = "image.png";
div.appendChild(canvas);
};
}
<div id="locations"></div>
<canvas id="myCanvas" width="75" height="75"></canvas>
Result Image

Use canvas.height and width values instead of CSS style. CSS style values applied after canvas drawn.
var div=document.getElementById("locations");
var canvas;
window.onload = function(){
for(var i=0;i<10;i++){
canvas=document.createElement("canvas");
canvas.width=75;
canvas.height=75;
var context = canvas.getContext("2d");
var imageObj = new Image();
imageObj.onload = function(){
context.drawImage(imageObj, 0, 0);
context.font = "17px Calibri";
context.fillText(i, 30, 36);
};
imageObj.src = "http://placehold.it/350x150";
div.appendChild(canvas);
};
}
<div id="locations"></div>

Canvas DrawImage does not work on IOS Safari

I have a canvas with an id called napkin. When I call the following function it is supposed to draw an image and the napkin canvas onto another canvas in memory. It works on every browser but IOS Safari. The operation does not seem to exceed the IOS memory cap for the canvas. I test this by calling k().toDataURL(). Any ideas?
function k() {
var canvas = document.createElement('canvas');
var napkin = document.getElementById("napkin");
var img = new Image();
img.src = picurl;
var ctx = canvas.getContext("2d");
var imgdata = new Image();
imgdata.src = napkin.toDataURL();
canvas.width = img.width;
canvas.height = img.height;
ctx.drawImage(img, 0, 0);
ctx.globalAlpha = 0.5;
ctx.drawImage(imgdata, 0, 0);
return canvas;
}

You need to wait for the image data to load before using it...
var img = new Image();
img.onload = function(){
// do stuff here with img
};
img.src = picurl;
// not here

How to write text on top of image in HTML5 canvas?

I want to display a image on canvas and insert a text on top of that image.
window.onload = function() {
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
var imageObj = new Image();
imageObj.onload = function() {
context.drawImage(imageObj, 10, 10);
};
imageObj.src = "darth-vader.jpg";
context.font = "40pt Calibri";
context.fillText("My TEXT!", 20, 20);
};
I'm getting only an image over here but not the text; the text is behind the image.
How to insert the text on top of the image?

That is because you draw the text before the image has loaded and been drawn. You have to draw the text that should be on top of the image after the image is drawn. Try this code instead:
window.onload = function(){
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
var imageObj = new Image();
imageObj.onload = function(){
context.drawImage(imageObj, 10, 10);
context.font = "40pt Calibri";
context.fillText("My TEXT!", 20, 20);
};
imageObj.src = "darth-vader.jpg";
};
Example:

On a canvas, difference between drawImage with png vs create a drawing using strokes?

Why is there a difference between how things are handled in a canvas? E.g if I put a png on the canvas vs draw a line on the canvas. When I copy that canvas's content to another canvas, only the line gets copied over.
var thecanvas = document.getElementById('mycanvas');
var context = thecanvas.getContext('2d');
// put a png on the canvas
var img = new Image();
img.onload = function(){ context.drawImage(img,0,0); };
img.src = 'images/test.png';
// draw a line on the canvas
context.moveTo(100, 150); context.lineTo(450, 50); context.stroke();
final_image = thecanvas.toDataURL("image/png");
copyimg = new Image();
copyimg.src = final_image;
var newcanvas = document.getElementById('newCanvas');
var newcanvascontext = newcanvas.getContext('2d');
// why is only the line I drew copied over and not the png image???
newcanvascontext.drawImage(copyimg,0,0,397,397);

Please note the image load event. Canvas is copied before the image gets loaded. You have to do like this
var thecanvas = document.getElementById('mycanvas');
var context = thecanvas.getContext('2d');
// put a png on the canvas
var img = new Image();
img.onload = function(){
context.drawImage(img,0,0);
var newcanvas = document.getElementById('newCanvas');
var newcanvascontext = newcanvas.getContext('2d');
newcanvascontext.drawImage(thecanvas,0 ,0);
};
img.src = 'http://www.mygreatiphone.com/wp-content/uploads/2011/11/google.png';
// draw a line on the canvas
context.moveTo(100, 150); context.lineTo(450, 50); context.stroke();
See the demo : http://jsfiddle.net/diode/3NHXy/5/