I tried canvas but can't find if there is any way to get all data, there is only single pixel information.
<!DOCTYPE html>
<html>
<body>
<canvas id="myCanvas" width="300" height="150" style="border:1px solid #3f3939;">
Your browser does not support the HTML5 canvas tag.</canvas>
<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = "red";
ctx.fillRect(10, 10, 100, 100);
function copy() {
var imgData = ctx.getImageData(10, 10, 50, 50);
ctx.putImageData(imgData, 20, 20);
}
</script>
<button onclick="copy()">Copy</button>
</body>
</html>
I'm working on image Decryption/Encryption methods, but first I want to get all image data at once, please anyone help.
Extending on my comment...
I'm not sure what you mean by "get all image data at once" the getImageData can return as much or little as you need, and it certainly is at once, we don't need to make multiple calls, we just change the parameters.
read more:
https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/getImageData
If you need the entire canvas you can do:
ctx.getImageData(0, 0, c.width, c.height)
var output = document.getElementById("output");
var ctx_output = output.getContext("2d");
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = "red";
ctx.fillRect(10, 10, 80, 80);
ctx.fillRect(99, 20, 20, 20);
function copy() {
var imgData = ctx.getImageData(0, 0, c.width, c.height);
ctx_output.putImageData(imgData, 0, 0);
}
<canvas id="myCanvas" width="200" height="100" style="border:1px solid #3f3939;">
Your browser does not support the HTML5 canvas tag.</canvas>
<br>
<button onclick="copy()">Copy</button>
<br>
<canvas id="output" width="200" height="100" style="border:1px solid #0000ff;">
Your browser does not support the HTML5 canvas tag.</canvas>
Related
I'm trying to load the image on canvas but it's not working:(
I checked functions and variables much time but I couldn't find any errors.
Help me to find the reasons why it can't be loaded.
When I run it on the tomcat server, only the canvas with aliceblue color is shown.
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Print image and text</title>
<script>
function drawPicture(ctx) {
var img = new Image();
img.addEventListener('load', function() {
ctx.drawImage(img, 20, 20, 100, 100);
ctx.font = "50px forte";
ctx.strokeStyle="blue";
ctx.fillStyle = "violet";
ctx.strokeText("Spongebob", 20, 100);
ctx.fillText("Spongebob", 20, 100);
}, false);
img.src = "spongebob.png";
}
</script>
</head>
<body>
<h3>Print image and text</h3>
<hr>
<canvas id="myCanvas" width="300" height="130"
style="background-color:aliceblue"></canvas>
<script>
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
drawPicture(context);
</script>
</body>
</html>
Your code is fine, here is an example with a different image...
<!DOCTYPE html>
<html>
<body>
<canvas id="myCanvas" width="300" height="130"></canvas>
<script>
function drawPicture(ctx) {
var img = new Image();
img.addEventListener('load', function() {
ctx.drawImage(img, 20, 20, 100, 100);
ctx.font = "50px forte";
ctx.strokeStyle = "blue";
ctx.fillStyle = "violet";
ctx.strokeText("Spongebob", 20, 100);
ctx.fillText("Spongebob", 20, 100);
}, false);
img.src = "http://i.stack.imgur.com/UFBxY.png";
}
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
drawPicture(context);
</script>
</body>
</html>
Only thing could be that the image you are trying to load does not exist...
As #Kaiido mentioned in the comments you need to debug this, check in your browser developer tools see if the image is loading correctly.
You should see something like:
instead of image.addEventListener, try doing image.onload?
You can instead of using the load event in the image, try adding the image directly on the canvas.
function drawPicture(ctx) {
var img = new Image();
img.src = "spongebob.png";
ctx.drawImage(img, 20, 20, 100, 100);
ctx.font = "50px forte";
ctx.strokeStyle="blue";
ctx.fillStyle = "violet";
ctx.strokeText("Spongebob", 20, 100);
ctx.fillText("Spongebob", 20, 100);
}
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
drawPicture(context);
<h3>Print image and text</h3>
<hr>
<canvas id="myCanvas" width="300" height="130"
style="background-color:aliceblue"></canvas>
I am trying to draw an image on a canvas, in HTML5. For some reason, the image simply isn't drawn onto the canvas, and there are no errors in the console. Here is my code:
<!DOCTYPE html>
<html>
<body>
<img id="image" src="Images/player.png"></img>
<canvas id="canvas" width="1000" height="750"></canvas>
<script>
var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");
var image = document.getElementById("image");
context.fillStyle = "lightblue";
context.fillRect(0, 0, 1000, 750);
context.drawImage(image, 0, 0);
</script>
</body>
</html>
Can somebody help? Thanks.
You need to add an event listener to the img tag called load. Then in the callback you can call drawImage with the provided img element.
You can do something like this - I have added one stackoverflow image for representation:
const canvas = document.getElementById("canvas");
const context = canvas.getContext("2d");
const image = document.getElementById("image");
context.fillStyle = "lightblue";
context.fillRect(0, 0, 1000, 750);
image.addEventListener('load', e => context.drawImage(image, 0, 0));
<img id="image" src="https://stackoverflow.blog/wp-content/themes/stackoverflow-oct-19/images2/header-podcast.svg" height="100px"></img>
<canvas id="canvas" width="1000" height="750"></canvas>
From the documentation: Drawing an image to the canvas
I hope this helps!
I'm using the canvas fillrect function to draw a number of rectangles. I'm hardcoding the coordinates at the moment, but is it possible to pass these to fill rect like a function call to the function? For example if I have 10 sets of coordinates, can I do that using a for loop or something and passing it to fillRect?
<body>
<canvas id="canvas1" width="1224" height="770" position="absolute" style="border:1px solid #d3d3d3;">
<script>
var canvas = document.getElementById("canvas1");
var ctx = canvas.getContext("2d");
ctx.fillStyle = "#FF0000";
ctx.fillRect(330,0,150,75);
ctx.fillStyle = "#FF4500";
ctx.fillRect(30,80,150,75);
</script>
Yeah it is easy something like this:
<body>
<canvas id="canvas1" width="1224" height="770" position="absolute" style="border:1px solid #d3d3d3;">
<script>
var canvas = document.getElementById("canvas1");
var ctx = canvas.getContext("2d");
function Generate(color,x,y,w,h)
{
ctx.fillStyle = color;
ctx.fillRect(x,y,w,h)
};
for(i=0;i<10;i++){
var height=100*i;
var width=50*i;
var x=i+(i*100);
var y=i+(i*120);
Generate("red",x,y,width,height);
}
</script>
</canvas>
</body>
Looks like getImageData works when I use FillRect to create a rect on the canvas, but it doesn't work when I draw a gif on the canvas despite it drawing correctly and everything. Have no idea why that is - is it a security risk? Help?
<html>
<body>
<p>Image to use:</p>
<img id="scream" width="230" height="60" src="http://www.thekitmaker.com/image/3.gif" alt="The Scream">
<p>Canvas:</p>
<canvas id="myCanvas" width="230" height="60" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.
</canvas>
<script>
function getPixel(imgData, index) {
var i = index*4, d = imgData.data;
return [d[i],d[i+1],d[i+2],d[i+3]] // [R,G,B,A]
}
// AND/OR
function getPixelXY(imgData, x, y) {
return getPixel(imgData, y*imgData.width+x);
}
window.onload = function() {
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
//draw on canvas
var img = document.getElementById("scream");
ctx.drawImage(img,10,10,50,50);//,0,0);// c.width,c.height);
//ctx.fillStyle = "red";
//ctx.fillRect(10, 10, 50, 50);
//get image data
alert("h");
var imgData = ctx.getImageData(10, 10, 50, 50);
alert("h2");
// The magic®
//getPixel(idt, 852); // returns array [red, green, blue, alpha]
alert("p:"+getPixelXY(idt,1,1)[0]); // same pixel using x,y
}
</script>
</body>
</html>
You are correct that it is because of security reasons. If you draw an image from a different origin onto a canvas, the canvas will be marked as "tainted" and you can no longer get image data from it, among other things.
Reference: http://www.w3.org/TR/html51/semantics.html#security-with-canvas-elements
When working on a canvas with javascript, is it possible to use ctx.fillText to return an input value?
something like this I guess:
(html)
(Customize:(input id="custom" value="Default Message" /)
(p)(button onclick="msg()")Try it(/button)(/p)
(canvas id="myCanvas" width="500" height="500")
(/canvas)
(/html)
(script)
var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
var message
message = document.getElementById("custom").value;
function msg(){
ctx.fillStyle = "rgb(255, 255, 255)";
ctx.font = "italic 800 30px Verdana";
ctx.fillText(message, 485, 245, 1000);
}
msg();
(/script)
So whatever the user types into the input will be drawn on the canvas when "Try It" is clicked. Is this possible or am I way off track?
Did you try your code? It's essentially fine, except that you need to determine the value of message within the msg() function so that it can change when the user changes it and, you should either pick a new color, or add color to the canvas so you can SEE it:
<body>
Customize:<input id="custom" value="Default Message" />
<p><button onclick="msg()">Try it</button></p>
<canvas style="background-color:#cccccc" id="myCanvas" width="500" height="500">
</canvas>
<script>
var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
var message;
function msg(){
message=document.getElementById('custom').value;
ctx.fillStyle = "rgb(255, 255, 255)";
ctx.font = "italic 800 30px Verdana";
ctx.fillText(message, 100, 245, 1000);
}
msg();
</script>
</body>