RGraph is a JavaScript charts library based on HTML5 SVG and canvas. RGraph is mature (over 15 years old) and has a wealth of features making it an ideal choice to use for showing charts on your website.

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Get the latest version of RGraph (version 6.18, 1st June 2024) from the download page. You can read the changelog here. There's also older versions available, minified files and links to cdnjs.com hosted libraries.

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RGraph can be used for free under the GPL or if that doesn't suit your situation there's an inexpensive (£129) commercial license available.

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The clearRect function

The clearRect function can be used to return a section of the canvas to transparency again - removing any drawing that might be there. It can be used to clear the canvas (assuming the dimensions are correct) without affecting the transformation matrix (ie any translate/scale/rotate/transform that you have done).

RGraph uses two functions to differentiate between using this function to clear the canvas and the way involving setting the width to itself - a clear function and a reset function. The reset function uses the width = width method of clearing the canvas (which also removes any anti-aliasing translation that has been done).

Arguments to the function

An example

    window.onload = function ()
        var canvas  = document.getElementById("cvs");
        var context = canvas.getContext('2d');
        var width   = canvas.width;
        var height  = canvas.height;

        // Clears the whole canvas
        context.clearRect(0, 0, width, height);