Unable to clear canvas - javascript

I am having a really difficult time resetting / clearning the contents of my canvas. I am currently using the : Sketch.js plugin to generate a free form canvas. It does exactly what I need it to, however, it does not seem to have an simple canvas 'reset' function call to clear the contents.
jsfiddle:
http://jsfiddle.net/k7fmq/
NOTE: I read that the 'width' method does not work in chrome, and both methods don't seem to work on a 'free-form' canvas, but only on shapes, which I did not test.
This is what I tried so far:
Markup
<div class="signature-field">
Signature:
<span class="sketch-container">
<canvas style="border:1px solid grey; border-radius:7px;" id="simple_sketch" width="400" height="150"></canvas>
<span class="save-signature">Save Signature</span>
<span class="reset-canvas">Reset Canvas</span>
</span>
Date: <input type="text"><br/><br/>Name: <input type="text">
</div>
JQuery (My latest attempt)
$('.reset-canvas').click(function() {
var myCanvas = document.getElementById("#simple_sketch");
var width = myCanvas.width;
myCanvas.width = width + 1;
});
Method 2:
$('.reset-canvas').click(function() {
canvas.width = canvas.width;
});
Method 3:
$('.reset-canvas').click(function() {
var myCanvas = document.getElementById("simple_sketch");
var ctx = myCanvas.getContext('2d');
ctx.clearRect(0, 0, myCanvas.width, myCanvas.height);
});

Try this: http://jsfiddle.net/k7fmq/1/
The sketchpad plugin keeps an array of "actions", and redraws them each update (which seems unnecessary, really, but whatevs).
var sktch = $('#simple_sketch').sketch(); // store a reference to the element.
var cleanCanvas = $('#simple_sketch')[0];
$('.save-signature').click(function(){
/* replace canvas with image */
var canvas = document.getElementById("simple_sketch");
var img = canvas.toDataURL("image/png");
$('#simple_sketch').replaceWith('<img src="'+img+'"/>');
$('.signature-buttons').replaceWith('');
});
$('.reset-canvas').click(function(){
sktch.sketch().actions = []; // this line empties the actions.
var myCanvas = document.getElementById("simple_sketch");
var ctx = myCanvas.getContext('2d');
ctx.clearRect(0, 0, myCanvas.width, myCanvas.height);
});

Try this:
var ctx = myCanvas.getContext('2d');
ctx.save();
ctx.setTransform(1, 0, 0, 1, 0, 0);
ctx.clearRect(0, 0, myCanvas.width, myCanvas.height);
ctx.restore();

Related

Trying to determine whether canvas is blank or not with javascript

I'm using the solution from: How to check if a canvas is blank? but it's not working. My blank canvas URL does not match the newly created canvas URL and I cannot figure out why. They are the same dimensions and everything but their .toDataURL return different things so there is no way for me to tell if it has been drawn in. Below is an example of what happens when I do .toDataURL on my blank canvas and .toDataURL on the newly created canvas, as you can see they differ as you continue along.
data:image/png;base64,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
data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAA0sAAACUCAYAAABCxLIRAAAKeUlEQVR4Xu3ZoRHAMAwEwbj/plOADY7/BotoZXKT8/kIECBAgAABAgQIECBA4BI4TAgQIECAAAECBAgQIEDgFhBLXgUBAgQIECBAgAABAgQeAmLJsyBAgAABAgQIECBAgIBY8gYIECBAgAABAgQIECDQBPxZak6mCBAgQIAAAQIECBAYExBLYwe3LgECBAgQIECAAAECTUAsNSdTBAgQIECAAAECBAiMCYilsYNblwABAgQIECBAgACBJiCWmpMpAgQIECBAgAABAgTGBMTS2MGtS4AAAQIECBAgQIBAExBLzckUAQIECBAgQIAAAQJjAmJp7ODWJUCAAAECBAgQIECgCYil5mSKAAECBAgQIECAAIExAbE0dnDrEiBAgAABAgQIECDQBMRSczJFgAABAgQIECBAgMCYgFgaO7h1CRAgQIAAAQIECBBoAmKpOZkiQIAAAQIECBAgQGBMQCyNHdy6BAgQIECAAAECBAg0AbHUnEwRIECAAAECBAgQIDAmIJbGDm5dAgQIECBAgAABAgSagFhqTqYIECBAgAABAgQIEBgTEEtjB7cuAQIECBAgQIAAAQJNQCw1J1MECBAgQIAAAQIECIwJiKWxg1uXAAECBAgQIECAAIEmIJaakykCBAgQIECAAAECBMYExNLYwa1LgAABAgQIECBAgEATEEvNyRQBAgQIECBAgAABAmMCYmns4NYlQIAAAQIECBAgQKAJiKXmZIoAAQIECBAgQIAAgTEBsTR2cOsSIECAAAECBAgQINAExFJzMkWAAAECBAgQIECAwJiAWBo7uHUJECBAgAABAgQIEGgCYqk5mSJAgAABAgQIECBAYExALI0d3LoECBAgQIAAAQIECDQBsdScTBEgQIAAAQIECBAgMCYglsYObl0CBAgQIECAAAECBJqAWGpOpggQIECAAAECBAgQGBMQS2MHty4BAgQIECBAgAABAk1ALDUnUwQIECBAgAABAgQIjAmIpbGDW5cAAQIECBAgQIAAgSYglpqTKQIECBAgQIAAAQIExgTE0tjBrUuAAAECBAgQIECAQBMQS83JFAECBAgQIECAAAECYwJiaezg1iVAgAABAgQIECBAoAmIpeZkigABAgQIECBAgACBMQGxNHZw6xIgQIAAAQIECBAg0ATEUnMyRYAAAQIECBAgQIDAmIBYGju4dQkQIECAAAECBAgQaAJiqTmZIkCAAAECBAgQIEBgTEAsjR3cugQIECBAgAABAgQINAGx1JxMESBAgAABAgQIECAwJiCWxg5uXQIECBAgQIAAAQIEmoBYak6mCBAgQIAAAQIECBAYExBLYwe3LgECBAgQIECAAAECTUAsNSdTBAgQIECAAAECBAiMCYilsYNblwABAgQIECBAgACBJiCWmpMpAgQIECBAgAABAgTGBMTS2MGtS4AAAQIECBAgQIBAExBLzckUAQIECBAgQIAAAQJjAmJp7ODWJUCAAAECBAgQIECgCYil5mSKAAECBAgQIECAAIExAbE0dnDrEiBAgAABAgQIECDQBMRSczJFgAABAgQIECBAgMCYgFgaO7h1CRAgQIAAAQIECBBoAmKpOZkiQIAAAQIECBAgQGBMQCyNHdy6BAgQIECAAAECBAg0AbHUnEwRIECAAAECBAgQIDAmIJbGDm5dAgQIECBAgAABAgSagFhqTqYIECBAgAABAgQIEBgTEEtjB7cuAQIECBAgQIAAAQJNQCw1J1MECBAgQIAAAQIECIwJiKWxg1uXAAECBAgQIECAAIEmIJaakykCBAgQIECAAAECBMYExNLYwa1LgAABAgQIECBAgEATEEvNyRQBAgQIECBAgAABAmMCYmns4NYlQIAAAQIECBAgQKAJiKXmZIoAAQIECBAgQIAAgTEBsTR2cOsSIECAAAECBAgQINAExFJzMkWAAAECBAgQIECAwJiAWBo7uHUJECBAgAABAgQIEGgCYqk5mSJAgAABAgQIECBAYExALI0d3LoECBAgQIAAAQIECDQBsdScTBEgQIAAAQIECBAgMCYglsYObl0CBAgQIECAAAECBJqAWGpOpggQIECAAAECBAgQGBMQS2MHty4BAgQIECBAgAABAk1ALDUnUwQIECBAgAABAgQIjAmIpbGDW5cAAQIECBAgQIAAgSYglpqTKQIECBAgQIAAAQIExgTE0tjBrUuAAAECBAgQIECAQBMQS83JFAECBAgQIECAAAECYwJiaezg1iVAgAABAgQIECBAoAmIpeZkigABAgQIECBAgACBMQGxNHZw6xIgQIAAAQIECBAg0ATEUnMyRYAAAQIECBAgQIDAmIBYGju4dQkQIECAAAECBAgQaAJiqTmZIkCAAAECBAgQIEBgTEAsjR3cugQIECBAgAABAgQINAGx1JxMESBAgAABAgQIECAwJiCWxg5uXQIECBAgQIAAAQIEmoBYak6mCBAgQIAAAQIECBAYExBLYwe3LgECBAgQIECAAAECTUAsNSdTBAgQIECAAAECBAiMCYilsYNblwABAgQIECBAgACBJiCWmpMpAgQIECBAgAABAgTGBMTS2MGtS4AAAQIECBAgQIBAExBLzckUAQIECBAgQIAAAQJjAmJp7ODWJUCAAAECBAgQIECgCYil5mSKAAECBAgQIECAAIExAbE0dnDrEiBAgAABAgQIECDQBMRSczJFgAABAgQIECBAgMCYgFgaO7h1CRAgQIAAAQIECBBoAmKpOZkiQIAAAQIECBAgQGBMQCyNHdy6BAgQIECAAAECBAg0AbHUnEwRIECAAAECBAgQIDAmIJbGDm5dAgQIECBAgAABAgSagFhqTqYIECBAgAABAgQIEBgTEEtjB7cuAQIECBAgQIAAAQJNQCw1J1MECBAgQIAAAQIECIwJiKWxg1uXAAECBAgQIECAAIEmIJaakykCBAgQIECAAAECBMYExNLYwa1LgAABAgQIECBAgEATEEvNyRQBAgQIECBAgAABAmMCYmns4NYlQIAAAQIECBAgQKAJiKXmZIoAAQIECBAgQIAAgTEBsTR2cOsSIECAAAECBAgQINAExFJzMkWAAAECBAgQIECAwJiAWBo7uHUJECBAgAABAgQIEGgCYqk5mSJAgAABAgQIECBAYExALI0d3LoECBAgQIAAAQIECDQBsdScTBEgQIAAAQIECBAgMCYglsYObl0CBAgQIECAAAECBJqAWGpOpggQIECAAAECBAgQGBMQS2MHty4BAgQIECBAgAABAk1ALDUnUwQIECBAgAABAgQIjAmIpbGDW5cAAQIECBAgQIAAgSYglpqTKQIECBAgQIAAAQIExgTE0tjBrUuAAAECBAgQIECAQBMQS83JFAECBAgQIECAAAECYwJiaezg1iVAgAABAgQIECBAoAmIpeZkigABAgQIECBAgACBMQGxNHZw6xIgQIAAAQIECBAg0ATEUnMyRYAAAQIECBAgQIDAmIBYGju4dQkQIECAAAECBAgQaAJiqTmZIkCAAAECBAgQIEBgTEAsjR3cugQIECBAgAABAgQINAGx1JxMESBAgAABAgQIECAwJvADO98Ald0HVn8AAAAASUVORK5CYII=
For reference here is the function:
function isCanvasBlank(canvas) {
var blank = document.createElement('canvas');
blank.width = canvas.width;
blank.height = canvas.height;
return canvas.toDataURL() == blank.toDataURL();
}
the resulting images you have are different. The first one has a white background and the other is transparent.
This is causing the difference.
this is a quick way to fill the new canvas.
function isCanvasBlank(canvas) {
var blank = document.createElement('canvas');
blank.width = canvas.width;
blank.height = canvas.height;
var ctx = blank.getContext("2d");
ctx.fillStyle = "#FFFFFF";
ctx.fillRect(0, 0, blank .width, blank .height);
return canvas.toDataURL() == blank.toDataURL();
}
or use same function as the fiddle. blank.getContext('2d').clearRect(0, 0, canvas.width, canvas.height);
function isCanvasBlank(canvas) {
var blank = document.createElement('canvas');
blank.width = canvas.width;
blank.height = canvas.height;
blank.getContext('2d').clearRect(0, 0, canvas.width, canvas.height);
return canvas.toDataURL() == blank.toDataURL();
}

Chrome not drawing specific jpg image in canvas

I'm trying to draw an image in a canvas. This works in Firefox but not in Chrome 49.
context.drawImage(backgroundImage, 0, 0);
JSFiddle: https://jsfiddle.net/kp5otnyu/3/
Image link: http://www.boardgame-online.com/img/stackoverflow_chrome_test.jpg
Something seems to be wrong with the image. We tried coping the image in another jpg that did draw, and then it worked. But what is wrong with this image?
EDIT: This is not an answer, all the cheers to #kaiido
Working example:
var backgroundImage = new Image();
var canvas = document.createElement("canvas");
var context = canvas.getContext("2d");
canvas.width = 500;
canvas.height = 100;
backgroundImage.onload = function(){
context.clearRect(0, 0, 300, 300);
context.drawImage(backgroundImage, 0, 0);
}
backgroundImage.src = "http://www.boardgame-online.com/img/stackoverflow_chrome_test.jpg";
$("#test").append(canvas);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.0.3/jquery.min.js"></script>
<div id="test">
</div>
Not Working example:
var backgroundImage = new Image();
var canvas = document.createElement("canvas");
var context = canvas.getContext("2d");
canvas.width = 400;
canvas.height = 400;
backgroundImage.onload = function(){
context.clearRect(0, 0, 300, 300);
context.drawImage(backgroundImage, 0, 0);
}
backgroundImage.src = "http://www.boardgame-online.com/img/stackoverflow_chrome_test.jpg";
$("#test").append(canvas);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.0.3/jquery.min.js"></script>
<div id="test">
</div>
This issue was solved in Chrome 50. When I open the JSFiddle in my updated Chrome, the image shows.

JS to apply to each canvas (multiple)

I want to use StackBlur.js on multiple canvas elements on the same page; however using the example provided by Zurb, I can only apply it to the first canvas element; it ignores the others.
Any idea how to make this code more universal to apply to every canvas element, not just to one?
The JS (by Zurb) is this:
$(function() {
// Change this value to adjust the amount of blur
var BLUR_RADIUS = 100;
var canvas = document.querySelector('[data-canvas]');
var canvasContext = canvas.getContext('2d');
var image = new Image();
image.src = document.querySelector('[data-canvas-image]').src;
var drawBlur = function() {
var w = canvas.width;
var h = canvas.height;
canvasContext.drawImage(image, 0, 0, w, h);
stackBlurCanvasRGBA('heroCanvas', 0, 0, w, h, BLUR_RADIUS);
};
image.onload = function() {
drawBlur();
}
});
The relevant HTML is this:
<canvas class="hero__background" id="heroCanvas" width="200" height="200" data-canvas></canvas>
<!-- Our image to be blurred -->
<img data-canvas-image style="display: none" src="path/to/image.jpg" />
Thank you!
Wrap their code in a loop over all elements with that attribute (in this case data-canvas) like so
$('[data-canvas]').each(function(){
var $el = $(this);
// insert their code here and change it to reference the correct image each time
});
So in the end you can refer to each of the canvases on the page individually, something like so:
$(function(){
// our iteration
$('[data-canvas]').each(function(){
var $el = $(this);
var BLUR_RADIUS = 100;
var canvas = this; // canvas is the element we're iterating over
var canvasContext = canvas.getContext('2d');
var image = new Image();
// I changed the line below of theirs to refer to the canvases attributes
// we're iterating over above
image.src = $el.attr('data-src');
var drawBlur = function() {
var w = canvas.width;
var h = canvas.height;
canvasContext.drawImage(image, 0, 0, w, h);
var id = $el.attr('id'); // use the id from the canvas
stackBlurCanvasRGBA( id, 0, 0, w, h, BLUR_RADIUS);
};
image.onload = function() {
drawBlur();
}
});
});
So now we don't need the images only their src attributes, which now live on the canvases asdata-src`. The the html can be as follows:
<canvas class="hero__background" id="heroCanvas1" data-src="/image/location.jpg" width="200" height="200" data-canvas></canvas>
<canvas class="hero__background" id="heroCanvas2" data-src="/image/location2.jpg" width="200" height="200" data-canvas></canvas>
Update: I realised that you're displaying info in the canvas, and so need more than one. code updated above.
Update 2: I realised that stack blur relies on an id for each call so you need to get that from each canvas in turn, updated code above
Aside: I would recommend iterating over the canvases by class not attribute, but I used it as that was what was in your html. I'd suggest adding a class to each and changing the iteration to something like so:
$('.blurImgCanvas').each(function(){....})

how to copy from one canvas to other canvas

here is the jsfiddle
i have this as my source canvas
HTML
<h1>Source Canvas</h1>
<canvas id="source" width=436 height=567></canvas>
<h1>Destination Canvas</h1>
<canvas id="destination" width=436 height=567></canvas>
javascript
var sourceImage, ctx, sourceCanvas, destinationCanvas;
//get the canvases
sourceCanvas = document.getElementById('source');
destinationCanvas = document.getElementById('destination');
//draw the source image to the source canvas
ctx = sourceCanvas.getContext('2d');
function start() {
ctx.drawImage(img1, 0, 0);
ctx.globalCompositeOperation = "source-atop";
var pattern = ctx.createPattern(img, 'repeat');
ctx.rect(0, 0, sourceCanvas.width, sourceCanvas.height);
ctx.fillStyle = pattern;
ctx.fill();
ctx.globalAlpha = .10;
ctx.drawImage(img1, 0, 0);
ctx.drawImage(img1, 0, 0);
ctx.drawImage(img1, 0, 0);
//ctx.globalAlpha = 1;
}
var img1 = new Image();
var img = new Image();
img.onload = function () {
img1.onload = function () {
start();
}
img1.src = "https://dl.dropboxusercontent.com/u/139992952/stackoverflow/4jiSz1.png";
}
img.src = "https://dl.dropboxusercontent.com/u/139992952/stackoverflow/BooMu1.png";
i want to to show what is in source canvas in my destination canvas.
i tired
var image, destinationCtx;
//create the image
image = new Image();
//get the base64 data
image.src = sourceCanvas.toDataURL('image/png');
//get the destination context
destinationCtx = destinationCanvas.getContext('2d');
//copy the data
destinationCtx.drawImage(image, 0, 0);
//done
but having no luck. am i missing something?
Copy via imageData,Copy via Base64 data,Copy via direct draw any method will do my job.
when i try with
http://jsperf.com/copying-a-canvas-element
it copies but when i put my source canvas writer it does not work ? am i missing something?
You can directly copy one canvas over other. Like this...
var destinationCtx;
//get the destination context
destinationCtx = destinationCanvas.getContext('2d');
//copy the data
destinationCtx.drawImage(sourceCanvas, 0, 0);
You can use getImageData from the source canvas and putImageData to the destination canvas.This is the fastest one compare to other ways.
var sourceCtx, destinationCtx, imageData;
sourceCtx = sourceCanvas.getContext('2d');
destinationCtx = destinationCanvas.getContext('2d');
imageData = sourceCtx.getImageData(0, 0, sourceCanvas.width - 1, sourceCanvas.height - 1);
destinationCtx.putImageData(imageData, 0, 0);
source:/ https://jsperf.com/copying-a-canvas-element

How to clone ImageData?

This is working, but I feel this code is lengthy.
I'm looking for better idea.
var clone = function(imageData) {
var canvas, context;
canvas = document.createElement('canvas');
canvas.width = imageData.width;
canvas.height = imageData.height;
context = canvas.getContext('2d');
context.putImageData(imageData, 0, 0);
return context.getImageData(0, 0, imageData.width, imageData.height);
};
The ImageData constructor accepts the image data array.
const imageDataCopy = new ImageData(
new Uint8ClampedArray(imageData.data),
imageData.width,
imageData.height
)
With TypedArray.prototype.set() you can directly copy the data.
var imageDataCopy = new Uint8ClampedArray(originalImageData.data);
imageDataCopy.data.set(originalImageData.data);
This sets the content of imageDataCopy to be identical to originalImageData.
Most times it should be sufficient to simply assign the imageData to a new variable, just like:
myImgData=ctx.getImageData(0,0,c.width,c.height); //get image data somewhere
imgDataCopy = myImgData; // clone myImgData
...now imgDataCopy contains a separate copy of myImgData. 🤷‍♂️
Demo
The snippet below creates 4 "frames" in an array of ImageData's and then loop through them.
const c = document.getElementById('canvas'),
ctx = c.getContext("2d");
var wh=70, iDatas=[], i=0,
lines=[[10,10,wh-10,wh-10], [wh/2,5,wh/2,wh-5], // ⤡,↕
[wh-10,10,10,wh-10], [5,wh/2,wh-5,wh/2]]; // ⤢,↔
c.width=wh;
c.height=wh;
ctx.strokeStyle='blue'; //setup to draw
ctx.lineWidth=9;
ctx.lineWidth='round';
for(var [x1,y1,x2,y2] of lines){
ctx.beginPath();
ctx.moveTo(x1,y1); //draw something
ctx.lineTo(x2,y2);
ctx.stroke();
var d=ctx.getImageData(0,0,c.width,c.height); //get imgdata
iDatas.push( d ); //save imgdata to array
ctx.clearRect(0, 0, c.width, c.height); //clear canvas
}
ctx.strokeStyle='green'; //❌has no effect:
// ↑ shows that color data comes from the source (can't be changed)
ctx.lineWidth='round'; //❌has no effect:
// ↑ shows that non-color styling does NOT come from source (CAN'T be changed)
//now you can refer to the image data as iData[i] where i= 0 to 3
drawFrame();
function drawFrame(){
ctx.putImageData( iDatas[i],0,0); //draw imgData from array
i=(i==3?0:i+1); //set next iteration #
setTimeout(function(){ drawFrame() }, 100); //schedule next frame
}
canvas{ border:2px dotted salmon; }
<canvas id='canvas'></canvas>

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