9Graphic and Multimedia Tools
The processing of data also requires graphic tools for visualization:
- – to draw directly into the web page, from data array (vector format);
- – to display pictures, from image or video sources (pixel format).
This chapter presents the HTML5 tools that JavaScript can use either for direct drawing (SVG or canvas) or multimedia display (images and videos). Displaying external sources requires sending an asynchronous request, whose return is handled, as seen in Chapter 8, by callbacks.
9.1. To draw in the web page
First, we need a surface onto which to place the drawing. There are three approaches, corresponding to the three following elements:
- – <iframe>: this opens a new window, placed in a rectangle of the target window, although it is actually a different window from a different HTTP request and with an independent
windowobject, and is hence a differentwindow.document, an independent JavaScript engine with its own global space, etc. This is the oldest way to proceed, before the AJAX technology. We ignore it in this book. - – <svg>: SVG is a markup language, like HTML, and can be run with a specific layout engine. We can display an <svg> page, just as we display an <html> page. Moreover, SVG shares several features with HTML: (a) a document model similar to the DOM, and which can be “embedded” as a branch of the DOM so that the HTML layout engine is capable handling it; (b) style rules in a CSS format, which can be included in the same style ...
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