I have used chart.js to generate a report page that has multiple charts. I need to export this report to PDF. There are many solutions available via search, but I cannot find one which has multiple canvas elements.
The only available solution seems to be to loop through all the images, and recreate the report using the images, and then download that as a pdf.
Is there any simpler/more efficient way to accomplish this?
<body>
<h1> Chart 1 </h1>
<div style="width:800px; height:400px;">
<canvas id="chart_1" width="50" height="50"></canvas>
</div>
<h1> Chart 2 </h1>
<div style="width:800px; height:400px;">
<canvas id="chart_2" width="50" height="50"></canvas>
</div>
<h1> Chart 3 </h1>
<div style="width:800px; height:400px;">
<canvas id="chart_3" width="50" height="50"></canvas>
</div>
</body>
Honestly, it seems like the easiest approach would be to just provide a "download to PDF" link that pops up the browser's print page and instruct to user to select "print as pdf".
If that approach doesn't work for you (or your users), then here is a rough way to do it.
Basically, we create a new canvas element that is the size of your report page and incrementally paint the pixels from your existing chart.js canvas charts into the new canvas. Once that is done, then you can use jsPDF to add the new canvas to a pdf document as an image and download the file.
Here is an example implementation that does just that.
$('#downloadPdf').click(function(event) {
// get size of report page
var reportPageHeight = $('#reportPage').innerHeight();
var reportPageWidth = $('#reportPage').innerWidth();
// create a new canvas object that we will populate with all other canvas objects
var pdfCanvas = $('<canvas />').attr({
id: "canvaspdf",
width: reportPageWidth,
height: reportPageHeight
});
// keep track canvas position
var pdfctx = $(pdfCanvas)[0].getContext('2d');
var pdfctxX = 0;
var pdfctxY = 0;
var buffer = 100;
// for each chart.js chart
$("canvas").each(function(index) {
// get the chart height/width
var canvasHeight = $(this).innerHeight();
var canvasWidth = $(this).innerWidth();
// draw the chart into the new canvas
pdfctx.drawImage($(this)[0], pdfctxX, pdfctxY, canvasWidth, canvasHeight);
pdfctxX += canvasWidth + buffer;
// our report page is in a grid pattern so replicate that in the new canvas
if (index % 2 === 1) {
pdfctxX = 0;
pdfctxY += canvasHeight + buffer;
}
});
// create new pdf and add our new canvas as an image
var pdf = new jsPDF('l', 'pt', [reportPageWidth, reportPageHeight]);
pdf.addImage($(pdfCanvas)[0], 'PNG', 0, 0);
// download the pdf
pdf.save('filename.pdf');
});
You can see it in action at this codepen.
Now let's talk about some gotchas with this approach. First, you have to control the position of each chart.js canvas in the new canvas object. The only way to do that is to have an understanding of how your report page is structured and implement that same structure. In my example, my charts are in a 2x2 grid and the logic handles this accordingly. If you had a 3x2 grid or something different then you would have to change the positioning logic.
Lastly, the final pdf output file dimensions are much larger than the original chart page (from the web). I think the reason is because my chart "container" div stretches across the full page. Therefore, you probably want to use a different approach for setting the size of your new canvas.
So long story short, the above example is meant to demonstrate an approach and not be your final solution.
Good luck!
I have a working solution in vanilla javascript(although I used ts typing) and using the lib jsPdf, where you need a plot per pdf page:
let index = 1;
// create new pdf object
// if don't choose compress as true you will end up with a large pdf file
let pdf = new jsPDF({
orientation: 'landscape',
unit: 'px',
format: 'a4',
compress: true,
})
// search for the html element(s) you need
const canvas = document.querySelectorAll("canvas");
// here my size are in pixels since I configured that in the obj instance
let pageWidth = 400;
let pageHeight = 400;
let index = 1;
// traverse the array of canvas
canvas.forEach( (canva:HTMLCanvasElement) => {
// I added some options among others I added the type of the compression
// method: FAST
pdf.addImage(canva, 'PNG', 10, 10, pageWidth, pageHeight, `img${index}`, "FAST");
// so as to not end up with an extra pdf page at the end of the iteration
if (index < canvas.length) {
pdf.addPage();
}
index++;
});
// download the pdf
pdf.save('Reporte.pdf');
Related
I'm looking to get some help or guidance on the use of the excellent libgif.js library.
My objective is to take a page that has an animated gif and a png of text with transparent background, and then show the 2 images overlaid such that the resulting image can be copied to the clipboard.
I've succeeded in doing this with a static image as a template
However, if I try this with a gif, it merges the animated gif with the text image, but freezes the gif.
I've familiarized myself with the libgif.js library and have succeeded in using it to build a canvas from an animated gif and have it remain animated.
However, the text image is not being displayed in the final canvas, and I'm a little lost as to how I might go about fixing this.
Is it obvious to anyone why the textImage is being properly sized and (somewhat) apparently placed on the canvas, but not displayed in the final result?
As a side question, does anyone know why the progress bar completes quickly at first and then progresses more slowly a second time?
The HTML is rather long, but the JS from the JSFiddle is shown below (for those not willing to click through to the link).
function doit() {
var isGIF = true; // always true for now TODO: better way to test if-gif than regex for ".gif"
var previewContainer = document.getElementById("previewContainer");
var textImage = document.getElementById("textImage");
var templateImage = document.getElementById("templateImage");
var w = document.getElementById("templateImage").width;
var h = document.getElementById("templateImage").height;
previewContainer.removeChild(previewContainer.children[1]);
if (isGIF) {
var gif = new SuperGif({
gif: templateImage,
progressbar_height: 5,
auto_play: true,
loop_mode: true,
draw_while_loading: true
});
gif.load();
var canvas = gif.get_canvas();
var context = canvas.getContext('2d');
context.drawImage(textImage, 0, 0, w, h);
previewContainer.replaceChild(canvas, previewContainer.children[0]);
}
}
Note: this solution was originally based on Arend's solution in the comments of this question from this JSFiddle.
You would have to tweak the library in order to get access to their rendering loop (like a frame_rendered event).
This way, you would be able to add whatever you want over the image the library drawn at every frame.
But since I'm too lazy to dig in there, here is a workaround :
Instead of appending the canvas returned by the library in the document, you can keep it offscreen, and draw it on an other, visible, canvas.
It is on this new canvas that you will also draw your textImage, in an rAF loop.
function doit() {
var previewContainer = document.getElementById("previewContainer");
var textImage = document.getElementById("textImage");
var templateImage = document.getElementById("templateImage");
var w = templateImage.width;
var h = templateImage.height;
previewContainer.removeChild(previewContainer.children[1]);
var gif = new SuperGif({
gif: templateImage,
progressbar_height: 5,
auto_play: true,
loop_mode: true,
draw_while_loading: true
});
gif.load();
var gif_canvas = gif.get_canvas(); // the lib canvas
// a copy of this canvas which will be appended to the doc
var canvas = gif_canvas.cloneNode();
var context = canvas.getContext('2d');
function anim(t) { // our animation loop
context.clearRect(0,0,canvas.width,canvas.height); // in case of transparency ?
context.drawImage(gif_canvas, 0, 0); // draw the gif frame
context.drawImage(textImage, 0, 0, w, h); // then the text
requestAnimationFrame(anim);
};
anim();
previewContainer.replaceChild(canvas, previewContainer.children[0]);
}
<script src="https://cdn.rawgit.com/buzzfeed/libgif-js/master/libgif.js"></script>
<div>
<input type="submit" id="doit" value="Do it!" onclick="doit()" />
</div>
<div id="previewContainer">
<img id="templateImage" src="https://i.imgur.com/chWt4Yg.gif" />
<img id="textImage" src="https://i.stack.imgur.com/CmErq.png" />
</div>
I am using jspdf and html2canvas combination to save html page as pdf. A pdf copy of current page is saved the moment you click a button. The problem is, if you zoom in the page, and then click the button, the saved pdf contains incomplete portion of the current page. Most of the part not visible on page due to zooming, gets cut off in the saved pdf page. What is the solution?
Below is the js code being invoked upon click of save button-
var pdf = new jsPDF('l', 'pt', 'a4');
var source = $('#someId')[0];
var options = {
background : '#eee'
};
pdf.addHTML(source, options, function(){
pdf.save('abcd.pdf');
});
EDIT
Taking idea from Saurabh's approach, I tried quite a similar thing, but without writing code for any extra div element. Before saving to pdf I made the screen size of a fixed width, and after printing I brought back the width back to default normal. It is working fine for, if it fails, we can always fix the height of the screen too, so that it appears fine in generated pdf despite zooming. Below is the code used by me:-
var pdf = new jsPDF('l', 'pt', 'a4');
var source = $('#someId')[0];
var options = {
background : '#eee'
};
var width = source.clientWidth;
source.style.width = '1700px';
pdf.addHTML(source, options,
function(){
pdf.save('abcd.pdf');
source.style.width = width+'px';
});
Here is how I managed to get the full page pdf while the page is zoomed in using jsPDF's new .html() method. First, I force the page zoom level back to 100% before converting it to pdf. It's important to reset the scale in html2canvas option after that, otherwise it'll returns a blank page.
<script src="https://cdnjs.cloudflare.com/ajax/libs/jspdf/1.5.3/jspdf.debug.js"
integrity="sha384-NaWTHo/8YCBYJ59830LTz/P4aQZK1sS0SneOgAvhsIl3zBu8r9RevNg5lHCHAuQ/"
crossorigin="anonymous"></script>
<script src="https://html2canvas.hertzen.com/dist/html2canvas.min.js"></script>
<!-- html2canvas 1.0.0-alpha.11 or higher version is needed -->
<script>
function download() {
// Bring the page zoom level back to 100%
const scale = window.innerWidth / window.outerWidth;
if (scale != 1) {
document.body.style.zoom = scale;
}
let pdf = new jsPDF('p', 'pt', 'a4');
pdf.html(document.getElementById('idName'), {
html2canvas: {
scale: 1 // default is window.devicePixelRatio
},
callback: function () {
// pdf.save('test.pdf');
window.open(pdf.output('bloburl')); // to debug
}
});
}
</script>
Update: A better way is to adjust the html2canvas.scale according to the scale factor.
function download() {
let pWidth = pdf.internal.pageSize.width; // 595.28 is the width of a4
let srcWidth = document.getElementById('idName').scrollWidth;
let margin = 18; // narrow margin - 1.27 cm (36);
let scale = (pWidth - margin * 2) / srcWidth;
let pdf = new jsPDF('p', 'pt', 'a4');
pdf.html(document.getElementById('idName'), {
x: margin,
y: margin,
html2canvas: {
scale: scale,
},
callback: function () {
window.open(pdf.output('bloburl'));
}
});
}
I was going through the same problem,
To do this what I did is I made a copy of printing div and while clicking print button I attached div copy to my dom with margin-top:500px
After I got its image then I hide this copy of the div, and set margin-top:0px
I hope this will work for you.
I'm working on a client's web design and development powered by Wordpress and Woocommerce, the plugin is great but there's a few functions I wish it had. The main one is giving the ability for the user to save the preview of their configuration.
The plug-in is 'Woocommerce Visual Products Configurator':
It allows buyers to build their own item by selecting from a series of different attributes for different parts of an item. Ex, choosing different types of Soles for a shoe, as well as being able to choose from a series of laces for the same shoe.
My Issue: The configuration images are layered on top of each other as the user selects their options so any normal "save as" function will just save the top image.
I have succesfully managed to combine and save the images using html2canvas-Data URL() but the way it generates the screenshots means the quality becomes very poor.
My thoughts are to merge all the images within the "vpc-preview" DIV then force the download.
Hunting through the functions of the plugin I found this:
function merge_pictures($images, $path = false, $url = false) {
$tmp_dir = uniqid();
$upload_dir = wp_upload_dir();
$generation_path = $upload_dir["basedir"] . "/VPC";
$generation_url = $upload_dir["baseurl"] . "/VPC";
if (wp_mkdir_p($generation_path)) {
$output_file_path = $generation_path . "/$tmp_dir.png";
$output_file_url = $generation_url . "/$tmp_dir.png";
foreach ($images as $imgs) {
list($width, $height) = getimagesize($imgs);
$img = imagecreatefrompng($imgs);
imagealphablending($img, true);
imagesavealpha($img, true);
if (isset($output_img)) {
imagecopy($output_img, $img, 0, 0, 0, 0, 1000, 500);
} else {
$output_img = $img;
imagealphablending($output_img, true);
imagesavealpha($output_img, true);
imagecopymerge($output_img, $img, 10, 12, 0, 0, 0, 0, 100);
}
}
imagepng($output_img, $output_file_path);
imagedestroy($output_img);
if ($path)
return $output_file_path;
if ($url)
return $output_file_url;
} else
return false;
}
However the function isn't called anywhere. There's also a couple of "save" buttons that are commented out which makes me wonder if they removed from a previous build.
Ideally I'd like the user to be able to instantly share their creation to facebook but thought this would be a good start.
Any ideas would be greatly appreciated!
Thanks!
UPDATE:
I've managed to use the following code to output an alert of the url's of each of the config images. Useless for the user but at least I know it's targeting exactly what I need.
function img_find() {
var imgs = document.querySelectorAll('#vpc-preview img');
var imgSrcs = [];
for (var i = 0; i < imgs.length; i++) {
imgSrcs.push(imgs[i].src);
}
return alert(imgSrcs);
}
Any suggestions on how to manipulate this and merge the corresponding image of each URL then force the download?
Cick to see Fiddle
UPDATE 2: The following fiddle lets users upload images and then merges them into a single photo for download. Unfortunately my coding skills aren't good enough to manipulate this into using the SRC urls of images within certain DIV and to Merge all the photos on top of each other.
Fiddle
function addToCanvas(img) {
// resize canvas to fit the image
// height should be the max width of the images added, since we rotate -90 degree
// width is just a sum of all images' height
canvas.height = max(lastHeight, img.width);
canvas.width = lastWidth + img.height;
ctx.clearRect(0, 0, canvas.width, canvas.height);
if (lastImage) {
ctx.drawImage(lastImage, 0, canvas.height - lastImage.height);
}
ctx.rotate(270 * Math.PI / 180); // rotate the canvas to the specified degrees
ctx.drawImage(img, -canvas.height, lastWidth);
lastImage = new Image();
lastImage.src = canvas.toDataURL();
lastWidth += img.height;
lastHeight = canvas.height;
imagesLoaded += 1;
}
Based on this question/answer, I would take a look at node-canvas.
What I have done in the past is use a #print css file to only capture the divs needed. Very simple concept but works well.
After looking at your link, that is exactly the situations I use it in..online designers. It is a little more difficult keeping your layers responsively aligned, but in the end I feel your codes become cleaner and it works well across devices and OS'.
If you dont want PDF and a simple preview and download than html2image.js is perfect.
$(document).ready(function(){
var element = $("#html-content-holder"); // global variable
var getCanvas; // global variable
$("#btn-Preview-Image").on('click', function () {
html2canvas(element, {
onrendered: function (canvas) {
$("#previewImage").append(canvas);
getCanvas = canvas;
}
});
});
$("#btn-Convert-Html2Image").on('click', function () {
var imgageData = getCanvas.toDataURL("image/png");
// Now browser starts downloading it instead of just showing it
var newData = imgageData.replace(/^data:image\/png/, "data:application/octet-stream");
$("#btn-Convert-Html2Image").attr("download", "your_pic_name.png").attr("href", newData);
});
});
<script src="https://github.com/niklasvh/html2canvas/releases/download/0.4.1/html2canvas.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<div id="html-content-holder" style="background-color: #F0F0F1; color: #00cc65; width: 500px;
padding-left: 25px; padding-top: 10px;">
Place any code here
</div>
<input id="btn-Preview-Image" type="button" value="Preview"/>
<a id="btn-Convert-Html2Image" href="#">Download</a>
<br/>
<h3>Preview :</h3>
<div id="previewImage">
</div>
For High quality you want to use rasterizeHTML.js
Found here:
https://github.com/cburgmer/rasterizeHTML.js/blob/master/examples/retina.html
I'm working in a Paper.js project where we're essentially doing image editing. There is one large Raster. I'm attempting to use the getSubRaster method to copy a section of the image (raster) that the user can then move around.
After the raster to edit is loaded, selectArea is called to register these listeners:
var selectArea = function() {
if(paper.project != null) {
var startDragPoint;
paper.project.layers[0].on('mousedown', function(event) { // TODO should be layer 0 in long run? // Capture start of drag selection
if(event.event.ctrlKey && event.event.altKey) {
startDragPoint = new paper.Point(event.point.x + imageWidth/2, (event.point.y + imageHeight/2));
//topLeftPointOfSelectionRectangleCanvasCoordinates = new paper.Point(event.point.x, event.point.y);
}
});
paper.project.layers[0].on('mouseup', function(event) { // TODO should be layer 0 in long run? // Capture end of drag selection
if(event.event.ctrlKey && event.event.altKey) {
var endDragPoint = new paper.Point(event.point.x + imageWidth/2, event.point.y + imageHeight/2);
// Don't know which corner user started dragging from, aggregate the data we have into the leftmost and topmost points for constructing a rectangle
var leftmostX;
if(startDragPoint.x < endDragPoint.x) {
leftmostX = startDragPoint.x;
} else {
leftmostX = endDragPoint.x;
}
var width = Math.abs(startDragPoint.x - endDragPoint.x);
var topmostY;
if(startDragPoint.y < endDragPoint.y) {
topmostY = startDragPoint.y;
} else {
topmostY = endDragPoint.y;
}
var height = Math.abs(startDragPoint.y - endDragPoint.y);
var boundingRectangle = new paper.Rectangle(leftmostX, topmostY, width, height);
console.log(boundingRectangle);
console.log(paper.view.center);
var selectedArea = raster.getSubRaster(boundingRectangle);
var selectedAreaAsDataUrl = selectedArea.toDataURL();
var subImage = new Image(width, height);
subImage.src = selectedAreaAsDataUrl;
subImage.onload = function(event) {
var subRaster = new paper.Raster(subImage);
// Make movable
subRaster.onMouseEnter = movableEvents.showSelected;
subRaster.onMouseDrag = movableEvents.dragItem;
subRaster.onMouseLeave = movableEvents.hideSelected;
};
}
});
}
};
The methods are triggered at the right time and the selection box seems to be the right size. It does indeed render a new raster for me that I can move around, but the contents of the raster are not what I selected. They are close to what I selected but not what I selected. Selecting different areas does not seem to yield different results. The content of the generated subraster always seems to be down and to the right of the actual selection.
Note that as I build the points for the bounding selection rectangle I do some translations. This is because of differences in coordinate systems. The coordinate system where I've drawn the rectangle selection has (0,0) in the center of the image and x increases rightward and y increases downward. But for getSubRaster, we are required to provide the pixel coordinates, per the documentation, which start at (0,0) at the top left of the image and increase going rightward and downward. Consequently, as I build the points, I translate the points to the raster/pixel coordinates by adding imageWidth/2 and imageHeight/2`.
So why does this code select the wrong area? Thanks in advance.
EDIT:
Unfortunately I can't share the image I'm working with because it is sensitive company data. But here is some metadata:
Image Width: 4250 pixels
Image Height: 5500 pixels
Canvas Width: 591 pixels
Canvas Height: 766 pixels
My canvas size varies by the size of the browser window, but those are the parameters I've been testing in. I don't think the canvas dimensions are particularly relevant because I'm doing everything in terms of image pixels. When I capture the event.point.x and event.point.y to the best of my knowledge these are image scaled coordinates, but from a different origin - the center rather than the top left. Unfortunately I can't find any documentation on this. Observe how the coordinates work in this sketch.
I've also been working on a sketch to illustrate the problem of this question. To use it, hold Ctrl + Alt and drag a box on the image. This should trigger some logging data and attempt to get a subraster, but I get an operation insecure error, which I think is because of security settings in the image request header. Using the base 64 string instead of the URL doesn't give the security error, but doesn't do anything. Using that string in the sketch produces a super long URL I can't paste here. But to get that you can download the image (or any image) and convert it here, and put that as the img.src.
The problem is that the mouse events all return points relative to 0, 0 of the canvas. And getSubRaster expects the coordinates to be relative to the 0, 0 of the raster item it is extracting from.
The adjustment needs to be eventpoint - raster.bounds.topLeft. It doesn't really have anything to do with the image width or height. You want to adjust the event points so they are relative to 0, 0 of the raster, and 0, 0 is raster.bounds.topLeft.
When you adjust the event points by 1/2 the image size that causes event points to be offset incorrectly. For the Mona Lisa example, the raster size (image size) is w: 320, h: 491; divided by two they are w: 160, h: 245.5. But bounds.topLeft of the image (when I ran my sketch) was x: 252.5, y: 155.5.
Here's a sketch that shows it working. I've added a little red square highlighting the selected area just to make it easier to compare when it's done. I also didn't include the toDataURL logic as that creates the security issues you mentioned.
Here you go: Sketch
Here's code I put into an HTML file; I noticed that the sketch I put together links to a previous version of the code that doesn't completely work.
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Rasters</title>
<script src="./vendor/jquery-2.1.3.js"></script>
<script src="./vendor/paper-0.9.25.js"></script>
</head>
<body>
<main>
<h3>Raster Bug</h3>
<div>
<canvas id="canvas"></canvas>
</div>
<div id="position">
</div>
</main>
<script>
// initialization code
$(function() {
// setup paper
$("#canvas").attr({width: 600, height: 600});
var canvas = document.getElementById("canvas");
paper.setup(canvas);
// show a border to make range of canvas clear
var border = new paper.Path.Rectangle({
rectangle: {point: [0, 0], size: paper.view.size},
strokeColor: 'black',
strokeWidth: 2
});
var tool = new paper.Tool();
// setup mouse position tracking
tool.on('mousemove', function(e) {
$("#position").text("mouse: " + e.point);
});
// load the image from a dataURL to avoid CORS issues
var raster = new paper.Raster(dataURL);
raster.position = paper.view.center;
var lt = raster.bounds.topLeft;
var startDrag, endDrag;
console.log('rb', raster.bounds);
console.log('lt', lt);
// setup mouse handling
tool.on('mousedown', function(e) {
startDrag = new paper.Point(e.point);
console.log('sd', startDrag);
});
tool.on('mousedrag', function(e) {
var show = new paper.Path.Rectangle({
from: startDrag,
to: e.point,
strokeColor: 'red',
strokeWidth: 1
});
show.removeOn({
drag: true,
up: true
});
});
tool.on('mouseup', function(e) {
endDrag = new paper.Point(e.point);
console.log('ed', endDrag);
var bounds = new paper.Rectangle({
from: startDrag.subtract(lt),
to: endDrag.subtract(lt)
});
console.log('bounds', bounds);
var sub = raster.getSubRaster(bounds);
sub.bringToFront();
var subData = sub.toDataURL();
sub.remove();
var subRaster = new paper.Raster(subData);
subRaster.position = paper.view.center;
});
});
var dataURL = ; // insert data or real URL here
</script>
</body>
</html>
I create a test code below and you can manipulate it on Jsfiddle:
http://jsfiddle.net/Stallman41/57hvX/31/
HTML:
<canvas id="test_canvas" style="background-color : #FFFF00" ; width="500px"
; height="340px"></canvas>
<br>
<button id="test_put_btn">Put an image</button>
<br>
<button id="save_dataURL">Save to dataURL</button>
<br>
<button id="draw_back">Final step: draw 3 images back.</button>
<br>
<img id="first_img"; width="100px" ; height="100px" ;></img>
<img id="second_img"; width="100px" ; height="100px" ></img>
<img id="third_img"; width="100px" ; height="100px" ;></img>
Javascript:
var drawing_plate;
var context;
var dataURL_arr = new Array();
$(document).ready(function () {
drawing_plate = document.getElementById("test_canvas");
context = drawing_plate.getContext('2d');
$("#test_canvas").bind("mousedown", Touch_Start);
$("#test_canvas").bind("mousemove", Touch_Move);
$("#test_canvas").bind("mouseup", Touch_End);
}); //document ready.
function Touch_Start(event) {
event.preventDefault();
touch = event;
touch_x = touch.pageX;
touch_y = touch.pageY;
line_start_x = touch.pageX - 0;
line_start_y = touch.pageY - 0;
context.beginPath();
context.moveTo(line_start_x, line_start_y);
}
function Touch_Move(event) {
event.preventDefault();
touch = event; //mouse
line_end_x = touch.pageX - 0;
line_end_y = touch.pageY - 0;
context.lineTo(line_end_x, line_end_y);
context.stroke();
}
$("#test_put_btn").click(function () {
var test_img = new Image();
test_img.src = "http://careerscdn.sstatic.net/careers/gethired/img/careers2- ad-header-so-crop.png";
context.drawImage(test_img, 0, 0);
});
$("#save_dataURL").click(function () {
dataURL_arr.push(drawing_plate.toDataURL("image/png"));
});
$("#draw_back").click(function () {
var f_image= $("#first_img")[0];
var s_image= $("#second_img")[0];
var t_image= $("#third_img")[0];
f_image.onload= function()
{
f_image.src= dataURL_arr[0];
}
f_image.src= dataURL_arr[0];
s_image.onload= function()
{
s_image.src= dataURL_arr[0];
}
s_image.src= dataURL_arr[0];
t_image.onload= function()
{
t_image.src= dataURL_arr[0];
}
t_image.src= dataURL_arr[0];
});
I develop a drawing plate on Android system, saving the drawings to a dataURL string. They can draw something on the canvas and put images on the canvas. And I need to let the users see their drawings on small icons.
I use canvas.toDataURL("image/png") to save the base64 string. And I choose <img> as the small icon container. However, what I got is only the drawings can be shown on the icon, and usually, when I write img.src= canvas.toDataURL("image/png"); the image shows nothing!
I investigate the issue for long time.
1. I think the problem might be the dataURL string is too long?
2. The support of the OS: Android?
The code in Jsfiddle here shows a similar procedure on my Android PhoneGap development.
First , you just draw something on the canvas, and press Press an image, and then Save to dataURL. But you should do the process three times. In this condition, the string array contains the base64 string generated by the drawings and the image.
In the final, you press Final step: draw 3 images back., nothing will be shown on the image icon.
In conclusion:
In my experience, as I write img.src= canvas.toDataURL("image/png"); (no matter the img is an dom element or var img = new Image();). It can't always work: sometimes it works... but sometimes not...(I work on Android 4.0.1, phonegap 1.7.0)
Second, especially if I store lots of base64 strings to an array, assigning them to lots of image DOM element, it definitely fails.
Third, if the user only draw something on the canvas, it can always work.( Except the example code in the Jsfiddle, but it works on my Android system...)
But if he draw an image context.drawImage(~) the image wouldn't show the pic.
Too much confusions...
I need to let the user can view their drawings in small icon, any alternative?
Some References:
1
2
3
I just stumbled across this question.
Click Put an image, then click Save to dataURL, then check your JavaScript console for something like:
SecurityError: DOM Exception 18
It's a browser security feature. Because you've inserted an image from a different domain, it counts as a cross-origin request.
If you eliminate the security error, you can export the canvas to a data URL.
Another thing in your code.
The image you try to draw onto the canvas into your test_put_btn onclick event handler, your image will never show up (or it will sometimes work accidentally) because you don't wait for your image to be loaded to draw it onto the canvas.
You have to handle the "onload" event of your image and draw it into the handler to permit the drawing of your image.
Before your test_img.src statement, you have to put :
test_img.onload = function()
{
context.drawImage(test_img, 0, 0);
};
Plus, the image you try to access is not accessible --> For me it does not work