If the source of the foreign content is an HTML or SVG element, attempting to retrieve the contents of the canvas isn't allowed. A tainted canvas is one which is no longer considered secure, and any attempts to retrieve image data back from the canvas will cause an exception to be thrown. Allowing cross-origin use of images and canvasīecause the pixels in a canvas's bitmap can come from a variety of sources, including images or videos retrieved from other hosts, it's inevitable that security problems may arise.Īs soon as you draw into a canvas any data that was loaded from another origin without CORS approval, the canvas becomes tainted.HTML table advanced features and accessibility.From object to iframe - other embedding technologies.
Assessment: Structuring a page of content. Another advantage is that you don't need to load every image individually, which can improve load performance. For instance, if you want to make a chart you could have a PNG image containing all the necessary text in a single file and depending on your data could change the scale of your chart fairly easily. You could have all elements in a single image file and use this method to composite a complete drawing. Slicing can be a useful tool when you want to make compositions. The last four parameters define the rectangle into which to draw the image on the destination canvas. The first four parameters define the location and size of the slice on the source image. To really understand what this does, it may help to look at this image: Given an image, this function takes the area of the source image specified by the rectangle whose top-left corner is ( sx, sy) and whose width and height are sWidth and sHeight and draws it into the canvas, placing it on the canvas at ( dx, dy) and scaling it to the size specified by dWidth and dHeight. drawImage(image, sx, sy, sWidth, sHeight, dx, dy, dWidth, dHeight) It lets us cut out a section of the source image, then scale and draw it on our canvas. The third and last variant of the drawImage() method has eight parameters in addition to the image source.
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