A Simple Smarty Modifier to Generate a Chart Through Google Chart API

After the longest title of my blog so far follows one of the shortest posts.

The function has two required parameters – the first one is provided automagically for you by smarty (it’s the value of the variable you’re applying the modifier to). This should be an array of objects containing the value you want to graph. The only required argument you have to provide to the modifier is the method to use for fetching the values for graphing.

Usage:
{$objects|googlechart:”getValue”}

This will dynamically load your plugin from the file modifier.googlechart.php in your Smarty plugins directory, or you can register the plugin manually by calling register_modifier on the template object after you’ve created it.

function smarty_modifier_googlechart($points, $method, $size = "600x200", $low = 0, $high = 0)
{
    $pointStr = '';
    $maxValue = 0;
    $minValue = INT_MAX;
    
    foreach($points as $point)
    {
        if ($point->$method() > $maxValue)
        {
            $maxValue = $point->$method();
        }

        if ($point->$method() < $minValue)
        {
            $minValue = $point->$method();
        }
    }

    if (!empty($high))
    {
        $maxValue = $high;
    }

    $scale = 100 / $maxValue;

    foreach($points as $point)
    {
        $pointStr .= (int) ($point->$method() * $scale) . ',';
    }

    $pointStr = substr($pointStr, 0, -1);

    // labels (5)
    $labels = array();

    $steps = 4;
    $interval = $maxValue / $steps;

    for($i = 0; $i < $steps; $i++)
    {
        $labels[] = (int) ($i * $interval);
    }

    $labels[] = (int) $maxValue;

    return 'http://chart.apis.google.com/chart?cht=lc&chd=t:' . $pointStr . '&chs=' . $size . '&chxt=y&chxl=0:|' . join('|', $labels);
}

The function does not support the short version of the Google Chart API Just Yet (tm) as it is an simple proof of concept hack made a few months ago.

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