I am using ESRI basemaps with Mapbox-GL-JS. I am trying to capture a screenshot of the map using the following code:
this.map.getCanvas().toBlob(function (blob) {
canvasContext.strokeStyle = '#CCCCCC';
canvasContext.strokeRect(leftPosition, topPosition, width, height);
var img = new Image();
img.setAttribute("crossOrigin", "anonymous");
var srcURL = URL.createObjectURL(blob);
img.onload = function () {
canvasContext.drawImage(img, leftPosition, topPosition, width, height);
URL.revokeObjectURL(srcURL);
};
img.src = srcURL;
});
I am not able to figure out why the attribution on the Map is not getting captured in the screenshot. I understand that here I am just trying to get the canvas of the map. I even tried adding text elements to the map canvas and that doesn't work either. I have markers & routes, which get in the image correctly. I also tried using the Mapbox basemap and try the same, but faced the same issue.
Any help is highly appreciated!
map.getCanvas() will only return the Map's canvas not any of the HTML Elements which sit over the map like the controls, Mapbox logo or attribution text. Sam Murphy has been working on an example showing how to capture the Map including the Logo and Attribution text to an image which you can see at https://github.com/mapbox/mapbox-gl-js/pull/6518/files.
Since we can't easily capture an HTML Element to an image in JavaScript the attribution text is re-created in a canvas drawn into the Image.
Related
I would like to two show a Chart and also present an url with a link to a bigger Chart. The small preview-image looks and works fine:
<canvas id="image"></canvas>
var ct1 = document.getElementById("image").getContext("2d");
ct1.canvas.width = document.getElementById("image").offsetWidth;
ct1.canvas.height = document.getElementById("image").offsetHeight;
var Chart1 = new Chart(ct1).Line(lineChartData1,options);
The canvas is wrapped in a div, that's why offsetWidth and offsetHeight (to fill this additional div-element). Cause of the responsive-design there is no fixed image. Anyway, this works perfectly. For the URL to the "bigger" image I want to have the URL. I know the toDataURL() will help.
var url = document.getElementById("image").toDataURL();
document.write(url);
There are two disturbing problems with it:
The URL with this way exisists and, but the image has no content.
I also want to give the canvas-image a new size, like I managed with ct1.canvas.width and ct1.canvas.height, but it seems I cannot add this to the toDataURL.
What's wrong with the code?
Okay, I think I got it. Chart.js is animating the charts, so the toDataURL() I mentioned in my first question rendered only an empty image. We have to initiate the toDataURL, not before the animation is done. We handle that with the options:
var options = {
onAnimationComplete: done
}
and a tiny function:
function done() {
console.log('done');
var url=document.getElementById("canvas").toDataURL();
document.getElementById("canvas_link").href=url;
}
I think that's all.
I have a canvas on one page that is built using fabricjs
can i send that canvas to another page so that it retains all its objects as it is with all their properties and attributes to be same aswell.
Sure you can, just export your canvas to JSON
var canvas = new fabric.Canvas('c');
data = JSON.stringify(canvas)
Now you can send that data using a post request or store it in a database or whatever you want.
canvas.loadFromJSON(data, canvas.renderAll.bind(canvas));
Example: http://jsfiddle.net/P9cEf/3/
The example uses two canvases one page, but the concept is the same.
Edit:
To download the image client side
var canvas1 = document.getElementById("c");
var image = canvas1.toDataURL("image/png").replace("image/png", "image/octet-stream");
window.location.href = image;
I'm building a mobile website which lets users upload photos from their camera.
I can get images from the users albums, and I can get images when the user takes a photo in iOS6 on iPhone4 and Android 4, but when the user takes a photo with an iPhone5 (also using iOS6), I get nothing. I can get the image from the users photo albums, but not when taking a photo.
here's the code and jsfiddle below
$('input#file_api').change(function(evt){
var image = evt.target.files[0];
var reader = new FileReader();
reader.onerror = (function(){alert('error reading file')});
reader.onload = (function(theFile) {
return function(e) {
// Render thumbnail.
var tempImg = new Image();
tempImg.src = reader.result;
tempImg.onload = function(){
var canvas = document.createElement('canvas');
canvas.width=tempImg.width;
canvas.height=tempImg.height;
var ctx = canvas.getContext("2d");
ctx.drawImage(tempImg,0,0);
$('body').append(canvas);
})(image);
reader.readAsDataURL(image);
I've got an example here http://jsfiddle.net/8DJUy/4/
If you use the file picker to get a photo, it will append the photo to the page.
If you take a photo with an iPhone5, it won't append anything. But at the same time, it doesn't error out either.
Any suggestions on how to get around this?
I can't quite figure out what the problem is with grabbing the photo.
The reason I'm grabbing the photos like this is that the file sizes are quite large when uploaded directly from the phone, and the use case does not require high resolution images, so I'm using the canvas to resize the image before uploading it.
Try this instead:
ctx.drawImage(tempImg, 0, 0, canvas.width, canvas.height);
I got this web service that gives me a (jpeg) image. What I want is take this image, convert it into a Data URI and display it on an HTML5 canvas, like that:
obj = {};
obj.xmlDoc = new window.XMLHttpRequest();
obj.xmlDoc.open("GET", "/cgi-bin/mjpegcgi.cgi?x=1",false, "admin", "admin");
obj.xmlDoc.send("");
obj.oCanvas = document.getElementById("canvas-processor");
obj.canvasProcessorContext = obj.oCanvas.getContext("2d");
obj.base64Img = window.btoa(unescape(encodeURIComponent( obj.xmlDoc.responseText )));
obj.img = new Image();
obj.src = 'data:image/jpeg;base64,' + obj.base64Img;
obj.img.src = obj.src
obj.canvasProcessorContext.drawImage(obj.img,0,0);
Unfortunately, this piece of code doesn't work; the image is not painted on the canvas at all (plus it seems to have width and height = 0, could it be not decoded correctly? I get no exceptions). img.src looks like data:image/jpeg;base64,77+977+977+977+9ABBKRklG....
Resolved: turns out I should have overridden the mime type with:
req.overrideMimeType('text/plain; charset=x-user-defined');
and set the response type with:
req.responseType = 'arraybuffer';
(see this. You should make an asynchronous request if you change the response type, too).
First you need to create an img element (which is hidden)
Then you do exactly what you have done except that you listen to your onload event on your img element.
When this event is launched you are able to get the width and height of your pictures so you can set your canvas to the same size.
The you can draw your image as you did in last line.
I am a beginner programmer in javascript. I don't use jQuery! And I want to make a simple game.
I am loading multiple images into canvas using
imageObj.onload = function(){}
I am using a keylistener for multiple keypresses so that the images could move on the diagonal while pressing both up and left keys by using smth like this:
function keydown_handler(e){my_key[String.fromCharCode(e.keyCode)] =
true; Move();}
My problem is that when I press the keys and move the images on the canvas the image flickers. I suppose this is because it loads the image every time I press a key. If this is true how can I load an image ONCE into memory and then RECALL that image from memory and change it's coordinates?
Thank you!
Well, what you really need to do is to create a render loop with javascript using requestAnimationFrame(), and render with the canvas element. Here's a really basic example of rendering with HTML5:
<!DOCTYPE html>
<html>
<body>
<canvas id="gameCanvas" width="800px" height="600px"></canvas>
<script type="text/javascript">
var canvas = document.getElementById('gameCanvas');
var context = canvas.getContext('2d');
var myImage = new Image();
var myImage.onload=function(){init();};
var myImage.src='location/of/image.png';
var imageX = 0, imageY = 0;
function render()
{
window.requestAnimationFrame(render);
// clear canvas
canvas.width = canvas.width;
context.drawImage(myImage, imageX, imageY);
imageX++;
imageY++;
}
function init()
{
window.requestAnimationFrame(render);
}
</script>
</body>
</html>
There will never be flicker when you're rendering through a canvas since the browser is already double buffering that rendering surface; and manually double buffering the canvas will actually produce a significant drop in framerate. What you're probably encountering (if you're rendering through a canvas) is tearing of the frame. Using requestAnimationFrame will resolve the tearing problem by essentially v-syncing the render (since it waits until the end of code execution to render).
Hopefully this will help you get started on the right path for rendering with HTML5.
What you are referring to is a very common problem when dealing with animations. The issue has less to do with what is stored in memory and more to do with the way an animation must be redrawn each time something changes. The most common method for avoiding this flickering issue is known as double buffering.
I have never done this using HTML5 specifically but after a quick search I found this article that may help you.
https://stackoverflow.com/a/2864533/594558