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September 6, 2012 20:12
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Workaround for bug in Firefox when rendering background images in HTML to a canvas
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<!DOCTYPE html> | |
<html> | |
<head> | |
<meta charset="utf-8" /> | |
<title>Test case for bug in Firefox where a background image in a SVG isn't rendered to the canvas unless a workaround is applied</title> | |
</head> | |
<body> | |
<canvas id="canvas" style="border:1px solid black;" width="200" height="200"></canvas> | |
<script type="text/javascript"> | |
var canvas = document.getElementById("canvas"), | |
html = '<div style="padding: 10px; width: 100%; height: 100%; background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABQAAAAUCAYAAACNiR0NAAAAKUlEQVQ4jWNYt27df2Lwo0ePiMIMowaOGjgsDSRWIbEWjxo4auCwNBAAenk4PB4atggAAAAASUVORK5CYII=);">' + | |
"You should see a chess board like background image here. If not enable workaroundFirefoxBug() in the source code." + | |
'</div>'; | |
function htmlToXml(html) { | |
var doc = document.implementation.createHTMLDocument(""); | |
doc.documentElement.innerHTML = html; | |
doc.documentElement.setAttribute("xmlns", doc.documentElement.namespaceURI); | |
return (new window.XMLSerializer()).serializeToString(doc.documentElement); | |
} | |
function getSvgForXml(html, width, height) { | |
return '<svg xmlns="http://www.w3.org/2000/svg" width="' + width + '" height="' + height + '">' + | |
'<foreignObject width="100%" height="100%">' + | |
html + | |
'</foreignObject>' + | |
'</svg>'; | |
} | |
function buildImageUrl(svg) { | |
return "data:image/svg+xml;charset=utf-8," + svg; | |
} | |
function drawSvgToCanvas(svg, canvas) { | |
var context = canvas.getContext("2d"); | |
var image = new window.Image(); | |
image.onload = function() { | |
context.drawImage(image, 0, 0); | |
}; | |
image.src = buildImageUrl(svg); | |
} | |
function workaroundFirefoxBug(backgroundImageUrl) { | |
var div = document.createElement("div"); | |
div.style.backgroundImage = "url(" + backgroundImageUrl + ")"; | |
document.getElementsByTagName("body")[0].appendChild(div); | |
} | |
window.onload = function () { | |
workaroundFirefoxBug("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABQAAAAUCAYAAACNiR0NAAAAKUlEQVQ4jWNYt27df2Lwo0ePiMIMowaOGjgsDSRWIbEWjxo4auCwNBAAenk4PB4atggAAAAASUVORK5CYII="); | |
drawSvgToCanvas(getSvgForXml(htmlToXml(html), canvas.width, canvas.height), canvas); | |
}; | |
</script> | |
</body> | |
</html> |
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