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

    protected function plot($gd, $x0, $y0, $x1, $y1, $x2, $y2, $x3, $y3)
    {
        /* plot any cubic Bezier curve */
        $n = 0;
        $i = 0;
        $xc = $x0 + $x1 - $x2 - $x3;
        $xa = $xc - 4 * ($x1 - $x2);
        $xb = $x0 - $x1 - $x2 + $x3;
        $xd = $xb + 4 * ($x1 + $x2);
        $yc = $y0 + $y1 - $y2 - $y3;
        $ya = $yc - 4 * ($y1 - $y2);
        $yb = $y0 - $y1 - $y2 + $y3;
        $yd = $yb + 4 * ($y1 + $y2);
        $fx0 = $x0;
        $fx1 = 0;
        $fx2 = 0;
        $fx3 = 0;
        $fy0 = $y0;
        $fy1 = 0;
        $fy2 = 0;
        $fy3 = 0;
        $t1 = $xb * $xb - $xa * $xc;
        $t2 = 0;
        $t = array();
        /* sub-divide curve at gradient sign changes */
        if ($xa == 0) {
            /* horizontal */
            if (abs($xc) < 2 * abs($xb)) {
                $t[$n++] = $xc / (2.0 * $xb);
            }
            /* one change */
        } else {
            if ($t1 > 0.0) {
                /* two changes */
                $t2 = sqrt($t1);
                $t1 = ($xb - $t2) / $xa;
                if (abs($t1) < 1.0) {
                    $t[$n++] = $t1;
                }
                $t1 = ($xb + $t2) / $xa;
                if (abs($t1) < 1.0) {
                    $t[$n++] = $t1;
                }
            }
        }
        $t1 = $yb * $yb - $ya * $yc;
        if ($ya == 0) {
            /* vertical */
            if (abs($yc) < 2 * abs($yb)) {
                $t[$n++] = $yc / (2.0 * $yb);
            }
            /* one change */
        } else {
            if ($t1 > 0.0) {
                /* two changes */
                $t2 = sqrt($t1);
                $t1 = ($yb - $t2) / $ya;
                if (abs($t1) < 1.0) {
                    $t[$n++] = $t1;
                }
                $t1 = ($yb + $t2) / $ya;
                if (abs($t1) < 1.0) {
                    $t[$n++] = $t1;
                }
            }
        }
        for ($i = 1; $i < $n; $i++) {
            if (($t1 = $t[$i - 1]) > $t[$i]) {
                $t[$i - 1] = $t[$i];
                $t[$i] = $t1;
                $i = 0;
            }
        }
        $t1 = -1.0;
        $t[$n] = 1.0;
        /* begin / end point */
        for ($i = 0; $i <= $n; $i++) {
            /* plot each segment separately */
            $t2 = $t[$i];
            /* sub-divide at $t[$i-1], $t[$i] */
            $fx1 = ($t1 * ($t1 * $xb - 2 * $xc) - $t2 * ($t1 * ($t1 * $xa - 2 * $xb) + $xc) + $xd) / 8 - $fx0;
            $fy1 = ($t1 * ($t1 * $yb - 2 * $yc) - $t2 * ($t1 * ($t1 * $ya - 2 * $yb) + $yc) + $yd) / 8 - $fy0;
            $fx2 = ($t2 * ($t2 * $xb - 2 * $xc) - $t1 * ($t2 * ($t2 * $xa - 2 * $xb) + $xc) + $xd) / 8 - $fx0;
            $fy2 = ($t2 * ($t2 * $yb - 2 * $yc) - $t1 * ($t2 * ($t2 * $ya - 2 * $yb) + $yc) + $yd) / 8 - $fy0;
            $fx0 -= $fx3 = ($t2 * ($t2 * (3 * $xb - $t2 * $xa) - 3 * $xc) + $xd) / 8;
            $fy0 -= $fy3 = ($t2 * ($t2 * (3 * $yb - $t2 * $ya) - 3 * $yc) + $yd) / 8;
            $x3 = floor($fx3 + 0.5);
            $y3 = floor($fy3 + 0.5);
            /* scale bounds to int */
            if ($fx0 != 0.0) {
                $fx1 *= $fx0 = ($x0 - $x3) / $fx0;
                $fx2 *= $fx0;
            }
            if ($fy0 != 0.0) {
                $fy1 *= $fy0 = ($y0 - $y3) / $fy0;
                $fy2 *= $fy0;
            }
            if ($x0 != $x3 || $y0 != $y3) {
                $this->plotCubicSegment($gd, $x0, $y0, $x0 + $fx1, $y0 + $fy1, $x0 + $fx2, $y0 + $fy2, $x3, $y3);
            }
            $x0 = $x3;
            $y0 = $y3;
            $fx0 = $fx3;
            $fy0 = $fy3;
            $t1 = $t2;
        }
    }