I've a <canvas> with an image already loaded and all the graphics coordinates needed for a crop (x, y, w, h) in an array.
What I'm trying to do is to crop the canvas directly, without a temporary other canvas to copy to/from (as suggested in other SO answers).
My idea is to:
1) Draw the selected area on the top-left corner of the canvas
2) Shrink the canvas size to the area
$('#edit').on("click", function() {
var img = $('#canvas');
var c = img[0];
var ctx = c.getContext("2d");
//var imageData = ctx.getImageData(0, 0, 100, 100);
ctx.drawImage(c, 0, 0, 100, 100, 0, 0, 100, 100);
c.width = 100;
c.height = 100;
});
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
ctx.fillStyle = "green";
ctx.fillRect(0, 0, 350, 350);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<canvas id="canvas" width="350" height="350"></canvas>
<input id="edit" type="button" value="Edit" />
Seems easy to me, but I'm missing something: when I execute, I get nothing https://jsfiddle.net/qg0znpu7/
What's wrong with my code? how can I fix it to obtain an in-place canvas crop?
Changing the width or height of a canvas will clear it. For that reason you will have to copy the data first.
You can use putImageData() for that:
$('#edit').on("click", function() {
var c = $('#canvas')[0];
var ctx = c.getContext("2d");
var imageData = ctx.getImageData(0, 0, 100, 100);
c.width = 100;
c.height = 100;
ctx.putImageData(imageData, 0, 0);
});
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
ctx.fillStyle = "green";
ctx.fillRect(0, 0, 350, 350);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<canvas id="canvas" width="350" height="350"></canvas>
<input id="edit" type="button" value="Edit" />
Related
I'm creating a pixel art app and when I want to save the image from the canvas the image is so small, so it seems pixelated when I want to resize it.
I want to resize it to bigger dimensions, but I don't know how.
This is the code example:
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.beginPath();
ctx.rect(0, 0, 50, 50);
ctx.fillStyle = 'red';
ctx.fill();
document.write('<img style="width:300px;" src="'+c.toDataURL("image/png")+'"/>');
// This is an image with dimensions 108x108px and it seems very bad when i resize it to 300x300px
// I want to download the canvas image with more resolution
<canvas id="myCanvas" width="108" height="108" style="width: 300px; height:300px;">
</canvas>
you can create a canvas and put the imageData in it.
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.beginPath();
ctx.rect(0, 0, 25, 25);
ctx.fillStyle = 'red';
ctx.fill();
ctx.beginPath();
ctx.rect(0, 25, 25, 25);
ctx.fillStyle = 'yellow';
ctx.fill();
ctx.beginPath();
ctx.rect(25, 0, 25, 25);
ctx.fillStyle = 'blue';
ctx.fill();
ctx.beginPath();
ctx.rect(25, 25, 25, 25);
ctx.fillStyle = 'green';
ctx.fill();
var c2 = document.createElement("canvas");
c2.width = 50;
c2.height = 50;
var ctx2 = c2.getContext("2d");
var imageData = ctx.getImageData(0, 0, 50, 50);
ctx2.putImageData(imageData, 0, 0);
document.write('<img style="width:300px;" src="' + c2.toDataURL("image/png") + '"/>');
My canvas is 512x256 pixels
Here is what I am trying to achieve :
Print a local image (image 1) on the canvas.
Fill this image with a specific color.
Print another local image(image 2) that should not overlap image 1.
So what I did is :
.drawImage(image1)
Create a rectangle of 512x256 ( ctx.rect(0, 0, 512, 256); )
ctx.globalCompositeOperation = "destination-in";
draw this rectangle ( ctx.fill() ) (with destination-in it should have for effect to fill the first image with the color of the rectangle)
ctx.globalCompositeOperation = "destination-out";
.drawImage(image2) (with destination-out it should make this image under the image 1)
But it doesn't display anything.
I figured it was because we can't have different globalCompositeOperation... But I'm sure it's possible somehow, I found people talking about it and fixing the issue but they're using specific code for their specific task and I simply don't understand. I would love an example for my script :
<script>
var c = document.getElementById("canvas");
var ctx = c.getContext("2d");
var img1 = new Image();
img1.onload = function () {
ctx.drawImage(img1, 0, 0);
};
ctx.globalCompositeOperation = "destination-in";
ctx.rect(0, 0, 512, 256);
ctx.fillStyle = "green";
ctx.fill()
ctx.globalCompositeOperation = "destination-out";
img2.onload = function () {
ctx.drawImage(img2, 0, 0);
};
img1.src = "C:/Users/... file1.png" // replaced the path for this example
img2.src = "C:/Users/... file2.png";
</script>
And here is my html body :
<body>
<canvas id="canvas" width="512" height="256"></canvas>
</body>
i am trying to draw a canvas line on div id "myCanvas" but problem is the line becomes very low resolution and its not shows smooth line. How can i increase that line resolution? And make it smooth line?
js:
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');
context.rect(0, 0, canvas.width, canvas.height);
var grd = context.createLinearGradient(100, 150, canvas.width, canvas.height);
grd.addColorStop(0, '#0132bf');
grd.addColorStop(1, '#ccd9ff');
context.fillStyle = grd;
context.fill();
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');
context.beginPath();
context.lineTo(-10, 190);
context.bezierCurveTo(200, -100, 500, 200, 400, 150);
context.lineWidth = .9;
context.strokeStyle = '#ccd9ff';
context.stroke();
jsfiddle link
Try giving your canvas HTML element width and height attributes that fit your requirements, for example:
<canvas id="myCanvas" width="600" height="600">
Here is my code. I am uploading a image and using like this :
> var canvas = document.createElement('canvas');
> var context = canvas.getContext('2d');
> context.drawImage(image, 0, 0);
This works fine but if I copy the imagedata like below to another canvas. It loads image partially.
var canvas = document.getElementById('myCanvas');
var context1 = canvas.getContext('2d');
context1.putImageData(context.getImageData(0, 0, image.width, image.height), 0, 0);
I tried same approach by creating two canvas and this code which worked fine but without image.
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = "red";
ctx.fillRect(0, 0, 300, 300);
var d = document.getElementById("myCanvas1");
var btx = d.getContext('2d');
var imgData = ctx.getImageData(0, 0, 300, 300);
btx.putImageData(imgData, 0, 0);
If i create two canvas it works fine but not like the above where I am using in memory canvas.
My HTML file has this :
<canvas id="myCanvas" width="960" height="960"></canvas>
<canvas id="myCanvas1" width="960" height="960"></canvas>
When you create canvases, you need to set their width manually. Default canvas size is 300x150. From here HTMLCanvasElement.
Something like this:
var canvas = document.createElement('canvas');
var context = canvas.getContext('2d');
canvas.width = image.width;
canvas.height = image.height;
context.drawImage(image, 0, 0);
To copy one canvas to another use drawImage rather than getImageData, setImageData That way you will use the GPU to move the pixels rather than the CPU. You also have the option to resize, crop, and apply a variety of FXs.
// create a copy of canvasSource
// returns the newly created canvas.
function copyCanvas(canvasSource){
var canvasCopy = document.createElement("canvas");
canvasCopy.width = canvasSource.width;
canvasCopy.height = canvasSource.height;
canvasCopy.getContext("2d").drawImage(canvasSource, 0, 0);
return canvasCopy;
}
html code :
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<script type="text/javascript">
function start() {
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
var image = new Image();
image.onload = function () {
ctx.drawImage(image, 69, 50);
//draw a circle
ctx.beginPath();
ctx.arc(100, 75, 10, 0, Math.PI * 2, true);
ctx.stroke();
};
image.src = 'xy-coordinates.jpg';
}
</script>
</head>
<img id="myImgId" alt="" src="xy-coordinates.jpg" />
<input type="button" value="submit" onclick="start()">
<canvas id="myCanvas" width="700" height="393"></canvas>
</body>
</html>
I'm trying to draw a circle on an image dynamically once I click the button.
The problem is after clicking the button, I'm getting an extra image (with the circle drawn) displayed on the screen rather drawing on original image.
My requirement is to draw a circle on an image which is already displayed.
UPDATED
<script>
function Draw(){
var img = document.getElementById("theImg");
var cnvs = document.getElementById("myCanvas");
cnvs.style.position = "absolute";
cnvs.style.left = img.offsetLeft + "px";
cnvs.style.top = img.offsetTop + "px";
var ctx = cnvs.getContext("2d");
ctx.beginPath();
ctx.arc(250, 210, 10, 0, 2 * Math.PI, false);
ctx.lineWidth = 3;
ctx.stroke();
}
</script>
<img id='theImg' src='xy-coordinates.jpg'>
<input type='button' value='Draw' onclick='draw()' ><br>
<canvas id='myCanvas' width="700" height="393"></canvas>
when < br > is used in html tag befor or after canvas there comes a huge distance betweein image and button r any tags i place in there. how to rectify it ?
You don't need to create one more image because canvas in fact is an image by itself. Place your canvas on top of the source image by setting its position to absolute, left and top same as the source image:
var img = document.getElementById("myImgId");
var c = document.getElementById("myCanvas");
c.style.position = "absolute";
c.style.left = img.offsetLeft;
c.style.top = img.offsetTop;
Then just draw into canvas:
var ctx = c.getContext("2d");
ctx.beginPath();
ctx.arc(100, 75, 10, 0, Math.PI * 2, true);
ctx.stroke();
UPDATE:
function Draw(){
var img = document.getElementById("theImg");
var cnvs = document.getElementById("myCanvas");
cnvs.style.position = "absolute";
cnvs.style.left = img.offsetLeft + "px";
cnvs.style.top = img.offsetTop + "px";
var ctx = cnvs.getContext("2d");
ctx.beginPath();
ctx.arc(250, 210, 200, 0, 2 * Math.PI, false);
ctx.lineWidth = 3;
ctx.strokeStyle = '#00ff00';
ctx.stroke();
}
#draw-btn {
font-size: 14px;
padding: 2px 16px 3px 16px;
margin-bottom: 8px;
}
<div>
<input id='draw-btn' type='button' value='Draw' onclick='Draw()' />
</div>
<img id='theImg' src='http://i.telegraph.co.uk/multimedia/archive/02351/cross-eyed-cat_2351472k.jpg'>
<canvas id='myCanvas' width='536px' height='536px'></canvas>
You are drawing one image on canvas, and second image with "img" tag (already displayed). you can't draw circle with canvas, on HTML tag.