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 show charts on your website.

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Get the latest version of RGraph (version 6.17) from the download page. 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 scale function

The scale function increases or decreases the size of the pixels on the canvas - scaling them up or scaling them down. If you use negative values the drawings you make may be off-canvas. So scaling the horizontal direction by 2 increases the x-axis pixel size making everything bigger, by 1 and it remains the same, by 0.5 makes things smaller and negative values cause the x-axis pixel system to begin being reversed - so they're actually off to the left of the canvas (which you can't then see).

Arguments to the function

An example

You can use the function like this:

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

        // This doubles the size of the canvas in both the X and Y directions
        context.scale(2, 2);
        context.moveTo(0, 0);
        context.lineTo(200, 200);