php heatmap

heatmap.php

<?php

$width = 300;
$height = 100;

$gradientColours = [
    'blue' => [
        'red'   => 0,
        'green' => 0,
        'blue'  => 255,
    ],
    'green' => [
        'red'   => 0,
        'green' => 255,
        'blue'  => 0,
    ],
    'yellow' => [
        'red'   => 255,
        'green' => 255,
        'blue'  => 0
    ],
    'red' => [
        'red'   => 255,
        'green' => 0,
        'blue'  => 0
    ],
    'white' => [
        'red'   => 255,
        'green' => 255,
        'blue'  => 255
    ]
];

$transitions = [
    [
        'start' => 0,
        'end' => 128,
        'startColour' => $gradientColours['blue'],
        'endColour' => $gradientColours['green']
    ],
    [
        'start' => 128,
        'end' => 192,
        'startColour' => $gradientColours['green'],
        'endColour' => $gradientColours['yellow']
    ],
    [
        'start' => 192,
        'end' => 240,
        'startColour' => $gradientColours['yellow'],
        'endColour' => $gradientColours['red']
    ],
    [
        'start' => 240,
        'end' => 256,
        'startColour' => $gradientColours['red'],
        'endColour' => $gradientColours['white']
    ]
];

foreach ($transitions as $transition) {
    $start     = $transition['start'];
    $end       = $transition['end'];
    $steps     = $end - $start;
    $colourOne = $transition['startColour'];
    $colourTwo = $transition['endColour'];

    for ($i = 0; $i < $steps; $i++) {
        $t = $i / $steps;
        $r = $colourTwo['red'] * $t + $colourOne['red'] * (1 - $t);
        $g = $colourTwo['green'] * $t + $colourOne['green'] * (1 - $t);
        $b = $colourTwo['blue'] * $t + $colourOne['blue'] * (1 - $t);
        $a = 127 - (($i + $start) / 255 * 127);

        $gradients[$i + $start] = [
            'red'   => $r,
            'green' => $g,
            'blue'  => $b,
            'alpha' => $a
        ];
    }
}

$heatmapAlpha = imagecreatetruecolor($width, $height);
$white = imagecolorallocate($heatmapAlpha, 255, 255, 255);
imagefilledrectangle($heatmapAlpha, 0, 0, $width - 1, $height - 1, $white);

// 8% opaque point
$black = imagecolorallocatealpha($heatmapAlpha, 0, 0, 0, 127 * 0.92);
$radius = 15;

// this will create black circles that have some transparency
// the idea is many of these transparent circles on top of each other
// will slowly create a more opaque spot (a more intense spot)
foreach ($points as $point) {
    for ($r = $radius; $r > 0; $r--) {
        imagefilledellipse($heatmapAlpha, $point['x'], $point['y'], $r, $r, $black);
    }
}

$heatmap = imagecreatetruecolor($width, $height);
imagesavealpha($heatmap, true);

for ($x = 0; $x < $width; $x++) {
    for ($y = 0; $y < $height; $y++) {
        // get intensity from heatmapAlpha
        $intensity = imagecolorsforindex($heatmapAlpha, imagecolorat($heatmapAlpha, $x, $y));

        // our mask colour, continue to next pixel
        if ($intensity['red'] == 255 && $intensity['green'] == 255 && $intensity['blue'] == 255) {
            continue;
        }

        // using the intensity get the colour
        $gradientColour = $gradients[255 - $intensity['red']];

        // create the colour
        $colour = imagecolorallocatealpha($heatmap, $gradientColour['red'], $gradientColour['green'], $gradientColour['blue'], $gradientColour['alpha']);

        // set the colour at that pixel
        imagesetpixel($heatmap, $x, $y, $colour);
    }
}

imagedestroy($heatmapAlpha);

imagepng($heatmap, '/save/heatmap/to/file.png');
imagedestroy($heatmap);