5.22. Example - Annotating a Plot Using a Callback
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## 5.22. Example - Annotating a Plot Using a Callback

This is an advanced example that uses a drawing callback to add annotations to a plot. More information on this topic can be found in Section 6.5, “Using Callbacks to Annotate Plots”, where this example is described in detail.

Example 5.22. Annotated Plot

    <?php
    # PHPlot Example: Annotating a plot using callbacks
    # Note: This example is coded for PHPlot > 5.0.7
    require_once 'phplot.php';

    # Get the Sales data. In real life, this would most likely come from
    # a database or external file. For this example, we will use 'random'
    # data, but with a fixed seed for repeatable results.
    function get_data()
    {
        mt_srand(1);
        $data = array();
        # Build an array with 12 arrays of (month_name, value):
        for ($month = 1; $month <= 12; $month++)
            $data[] = array(strftime('%b', mktime(12, 0, 0, $month, 1)),
                            5 + mt_rand(5, 40));
        return $data;
    }

    # Find the best and worst sales data.
    # Gets the Y value (sales data) and X value. For PHPlot text-data data,
    # the X values are assigned as 0.5, 1.5, 2.5, etc.
    # The data array is in 'text-data' format: array of array(label, Y)...
    function get_best_worst($data,
        &$best_index, &$best_sales, &$worst_index, &$worst_sales)
    {
      $best_sales = NULL;
      $worst_sales = NULL;
      foreach ($data as $x => $point) {
          if (!isset($best_sales) || $point[1] > $best_sales) {
              $best_sales = $point[1];
              $best_index = $x + 0.5;
          }
          if (!isset($worst_sales) || $point[1] < $worst_sales) {
              $worst_sales = $point[1];
              $worst_index = $x + 0.5;
          }
      }
    }

    # Plot annotation callback.
    # The pass-through argument is the PHPlot object.
    function annotate_plot($img, $plot)
    {
        global $best_index, $best_sales, $worst_index, $worst_sales;

        # Allocate our own colors, rather than poking into the PHPlot object:
        $red = imagecolorresolve($img, 255, 0, 0);
        $green = imagecolorresolve($img, 0, 216, 0);

        # Get the pixel coordinates of the data points for the best and worst:
        list($best_x, $best_y) = $plot->GetDeviceXY($best_index, $best_sales);
        list($worst_x, $worst_y) = $plot->GetDeviceXY($worst_index, $worst_sales);

        # Draw ellipses centered on those two points:
        imageellipse($img, $best_x, $best_y, 50, 20, $green);
        imageellipse($img, $worst_x, $worst_y, 50, 20, $red);

        # Place some text above the points:
        $font = '3';
        $fh = imagefontheight($font);
        $fw = imagefontwidth($font);
        imagestring($img, $font, $best_x-$fw*4, $best_y-$fh-10,
                    'Good Job!', $green);

        # We can also use the PHPlot internal function for text.
        # It does the center/bottom alignment calculations for us.
        # Specify the font argument as NULL or '' to use the generic one.
        $plot->DrawText('', 0, $worst_x, $worst_y-10, $red,
                     'Bad News!', 'center', 'bottom');
    }

    # Begin main processing:

    # Fill the data array:
    $data = get_data();

    # Find the best and worst months:
    get_best_worst($data, $best_index, $best_sales, $worst_index, $worst_sales);

    # Create the PHPlot object, set title, plot type, data array type, and data:
    $plot = new PHPlot(800, 600);
    $plot->SetTitle('Monthly Widget Sales');
    $plot->SetPlotType('bars');
    $plot->SetDataType('text-data');
    $plot->SetDataValues($data);
    # Borders are needed for the manual:
    $plot->SetImageBorderType('plain');

    # Select X data labels (not tick labels):
    $plot->SetXTickPos('none');
    $plot->SetXTickLabelPos('none');
    $plot->SetXDataLabelPos('plotdown');

    # Format Y labels as "$nM" with no decimals, steps of 5:
    $plot->SetYLabelType('data', 0, '$', 'M');
    $plot->SetYTickIncrement(5.0);

    # Force the bottom of the plot to be at Y=0, and omit
    # the bottom "$0M" tick label because it looks odd:
    $plot->SetPlotAreaWorld(NULL, 0);
    $plot->SetSkipBottomTick(True);

    # Establish the drawing callback to do the annotation:
    $plot->SetCallback('draw_all', 'annotate_plot', $plot);

    # Draw the graph:
    $plot->DrawGraph();

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