Polygon

polygon.php

<?php

class Polygon {
    /**
     * @var array
     */
    protected $polygon = [];

    /**
     * Polygon itself, with basic vector-based structure
     * Array: [ [1,1], [2,1], [3,0], [2,-1] ]
     *
     * @var $polygon array
     */
    public function setPolygon($polygon) {
        if (count($polygon) < 3) {
            return false;
        }
        
        if (!isset($polygon[0]['x'])) {
            foreach ($polygon as &$point) {
                $point = ['x' => $point[0], 'y' => $point[1]];
            }
        }

        $this->polygon = $polygon;
    }

    /**
     * Check if $polygon contains $test value
     *
     * @var $test array(x=>decimal, y=>decimal)
     */
    public function calc($test) {
        $q_patt= [[0, 1], [3, 2]];

        $end = end($this->polygon);
        
        $pred_pt = end($this->polygon);
        $pred_pt['x'] -= $test['x'];
        $pred_pt['y'] -= $test['y'];

        $pred_q = $q_patt[$pred_pt['y'] < 0][$pred_pt['x'] < 0];
        $w = 0;
        
        for ($iter = reset($this->polygon); $iter !== false; $iter = next($this->polygon)) {
            $cur_pt = $iter;
            $cur_pt['x'] -= $test['x'];
            $cur_pt['y'] -= $test['y'];
            $q = $q_patt[$cur_pt['y'] < 0][$cur_pt['x'] < 0];

            switch ($q - $pred_q) {
                case -3:
                    ++$w;
                    break;
                case 3:
                    --$w;
                    break;
                case -2:
                    if ($pred_pt['x'] * $cur_pt['y'] >= $pred_pt['y'] * $cur_pt['x']) {
                        ++$w;
                    }
                    break;
                case 2:
                    if (!($pred_pt['x'] * $cur_pt['y'] >= $pred_pt['y'] * $cur_pt['x'])) {
                        --$w;
                    }
                    break;
            }

            $pred_pt = $cur_pt;
            $pred_q = $q;
        }

        return $w != 0;
    }
}