<?php

// Martin Hozik
// 24.5.2008
// doublethink.cleverweb.cz
session_start();
// inicializace
require __DIR__ . '/imagelightnessat.func.php';
require __DIR__ . '/linear_perspective.class.php';
$perspective = new linear_perspective();

// konfigurace rozměrů a pozic
$matrix_dim = ['x' => 80, 'y' => 30];
$captcha_dim = ['x' => 300, 'y' => 90];
$distance = ['x' => 1, 'y' => 1, 'z' => 1];
$metric = ['x' => 10, 'y' => 20, 'z' => 5];
$offset = ['x' => 0, 'y' => -60];

// matrice
$matrix = imagecreatetruecolor($matrix_dim['x'], $matrix_dim['y']);
$black = imagecolorexact($matrix, 0, 0, 0);
$white = imagecolorexact($matrix, 255, 255, 255);
imagefill($matrix, 0, 0, $white);

// font calibri neni kvůli licenčním podmínkám připojen, použijte jakýkoliv svůj
imagefttext($matrix, 20, 0, 2, 25, $black, __DIR__ . '/3DCaptcha.ttf', $_SESSION['captcha']);

// výpočet bodů ve 3d
$point = [];
for ($x = 0; $x < $matrix_dim['x']; ++$x) {
    for ($y = 0; $y < $matrix_dim['y']; ++$y) {
        $lightness = imagelightnessat($matrix, $x, $y);
        $point[$x][$y] = $perspective->get_projection(['x' => $x * $metric['x'] + $distance['x'], 'y' => $lightness * $metric['y'] + $distance['y'], 'z' => ($matrix_dim['y'] - $y) * $metric['z'] + $distance['z']]);
    }
}
imagedestroy($matrix);

// obrázek captcha
$captcha = imagecreatetruecolor($captcha_dim['x'], $captcha_dim['y']);

// antialiasing čar - pro menší zátěž lze vypnout
//imageantialias($captcha, true);

$black = imagecolorexact($captcha, 255, 0, 0);
$white = imagecolorexact($captcha, 255, 255, 255);
imagefill($captcha, 0, 0, $white);

// vykreslení vrstevnic
for ($x = 1; $x < $matrix_dim['x']; ++$x) {
    for ($y = 1; $y < $matrix_dim['y']; ++$y) {
        imageline($captcha, -$point[$x - 1][$y - 1]['x'] + $offset['x'], -$point[$x - 1][$y - 1]['y'] + $offset['y'], -$point[$x][$y]['x'] + $offset['x'], -$point[$x][$y]['y'] + $offset['y'], $black);
    }
}

// výstup
header('Content-type: image/png');
imagepng($captcha);