Grafika\Gd\DrawingObject\CubicBezier::plotLine PHP Method

    protected function plotLine($gd, $x0, $y0, $x1, $y1)
    {
        /* draw a black (0) anti-aliased line on white (255) background */
        $dx = abs($x1 - $x0);
        $sx = $x0 < $x1 ? 1 : -1;
        $dy = -abs($y1 - $y0);
        $sy = $y0 < $y1 ? 1 : -1;
        $err = $dx + $dy;
        $e2 = $x2 = 0;
        /* $error value e_xy */
        $ed = $dx - $dy == 0 ? 1 : sqrt((double) $dx * $dx + (double) $dy * $dy);
        for (;;) {
            /* pixel loop */
            $this->setPixel($gd, $x0, $y0, abs($err - $dx - $dy) / $ed);
            $e2 = $err;
            $x2 = $x0;
            if (2 * $e2 + $dx >= 0) {
                /* x step */
                if ($x0 == $x1) {
                    break;
                }
                if ($e2 - $dy < $ed) {
                    $this->setPixel($gd, $x0, $y0 + $sy, ($e2 - $dy) / $ed);
                }
                $err += $dy;
                $x0 += $sx;
            }
            if (2 * $e2 + $dy <= 0) {
                /* y step */
                if ($y0 == $y1) {
                    break;
                }
                if ($dx - $e2 < $ed) {
                    $this->setPixel($gd, $x2 + $sx, $y0, ($dx - $e2) / $ed);
                }
                $err += $dx;
                $y0 += $sy;
            }
        }
    }