Model/Product/Image.php
private function fastlyRotate($angle)
    {
        $angle = (int) $angle;

        $orient = null;
        if ($angle == 90) {
            $orient = 'r';
        }

        if ($angle == -90 || $angle == 270) {
            $orient = 'l';
        }

        if ($angle == 180) {
            $orient = 3;
        }

        if ($orient !== null) {
            $this->fastlyParameters['orient'] = $orient;
        }

        return $this;
    }
private function fastlyRotate($angle)
    {
        $angle = (int) $angle;

        $orient = null;
        if ($angle == 90) {
            $orient = 'r';
        }

        if ($angle == -90 || $angle == 270) {
            $orient = 'l';
        }

        if ($angle == 180) {
            $orient = 3;
        }

        if ($orient !== null) {
            $this->fastlyParameters['orient'] = $orient;
        }

        return $this;
    }
Fastly implementation of rotation

@param int $angle
@return \Magento\Catalog\Model\Product\Image