How to check intersection between 2 rotated rectangles?

Question

Can someone explain how to check if one rotated rectangle intersect other rectangle?

Answer 1

Maybe it will help someone. The same algorithm in PHP:

function isPolygonsIntersecting($a, $b) {
    $polygons = array($a, $b);

    for ($i = 0; $i < count($polygons); $i++) {
        $polygon = $polygons[$i];

        for ($i1 = 0; $i1 < count($polygon); $i1++) {
            $i2 = ($i1 + 1) % count($polygon);
            $p1 = $polygon[$i1];
            $p2 = $polygon[$i2];

            $normal = array(
                "x" => $p2["y"] - $p1["y"], 
                "y" => $p1["x"] - $p2["x"]
            );

            $minA = NULL; $maxA = NULL;
            for ($j = 0; $j < count($a); $j++) {
                $projected = $normal["x"] * $a[$j]["x"] + $normal["y"] * $a[$j]["y"];
                if (!isset($minA) || $projected < $minA) {
                    $minA = $projected;
                }
                if (!isset($maxA) || $projected > $maxA) {
                    $maxA = $projected;
                }
            }

            $minB = NULL; $maxB = NULL;
            for ($j = 0; $j < count($b); $j++) {
                $projected = $normal["x"] * $b[$j]["x"] + $normal["y"] * $b[$j]["y"];
                if (!isset($minB) || $projected < $minB) {
                    $minB = $projected;
                }
                if (!isset($maxB) || $projected > $maxB) {
                    $maxB = $projected;
                }
            }

            if ($maxA < $minB || $maxB < $minA) {
                return false;
            }
        }
    }

    return true;
}