<?php // content="text/plain; charset=utf-8"
require_once ('jpgraph/jpgraph.php');
require_once ('jpgraph/jpgraph_line.php');

// Callback to negate the argument
function _cb_negate($aVal) {
    return round(-$aVal);
}

// A fake depth curve
$ydata = array(0,1,4,5,8,9,10,14,16,16,16,18,20,20,20,22,22.5,22,19,19,15,15,15,15,10,10,10,6,5,5,5,4,4,2,1,0);

$n = count($ydata);
$y2data = array();
for( $i=0; $i< $n; ++$i ) {
    $y2data[] = $ydata[$i]+10;
}

// Negate all data
$n = count($ydata);
for($i=0; $i<$n; ++$i) {
    $ydata[$i] = round(-$ydata[$i]);
    $y2data[$i] = round(-$y2data[$i]);
}

// Basic graph setup
$graph = new Graph(400,300);
$graph->clearTheme();
$graph->SetScale("linlin");
$graph->SetY2Scale("lin");
$graph->SetMargin(50,50,60,40);
$graph->SetMarginColor('darkblue');
$graph->SetColor('darkblue');

// Setup titles
$graph->title->Set("Inverting both Y-axis");
$graph->title->SetFont(FF_FONT1,FS_BOLD);
$graph->title->SetColor("white");

$graph->subtitle->Set("(Negated Y & Y2 axis)");
$graph->subtitle->SetFont(FF_FONT1,FS_NORMAL);
$graph->subtitle->SetColor("white");

// Setup axis
$graph->yaxis->SetLabelFormatCallback("_cb_negate");
$graph->xaxis->SetColor("lightblue","white");
$graph->yaxis->SetColor("lightblue","white");
$graph->ygrid->SetColor("blue");

// Setup Y2 axis
$graph->y2axis->SetLabelFormatCallback("_cb_negate");
$graph->y2axis->SetColor("darkred","white");
$graph->y2scale->SetAutoMax(0); // To make sure it starts with 0

// Setup plot 1
$lp1 = new LinePlot($ydata);
$lp1->SetColor("yellow");
$lp1->SetWeight(2);
$graph->Add($lp1);

// Setup plot 2
$lp2 = new LinePlot($y2data);
$lp2->SetColor("darkred");
$lp2->SetWeight(2);
$graph->AddY2($lp2);

$graph->Stroke();
?>