Draw filled Text on cv::Mat? (OpenCV C++)

Question

I'm attempting to draw some filled text onto an image stored in a cv::Mat object using OpenCV's C++ library.

---

Most of the existing tutorials out there make use of the putText function.

The following minimal example:

#include <opencv2/opencv.hpp>
#include <opencv2/core/mat.hpp>
#include <opencv2/core/core.hpp>

int main()
{
    cv::Mat img = cv::Mat::zeros(300, 300, CV_8UC3);

    cv::putText(img, "TEST", cv::Point(50, 150), cv::FONT_HERSHEY_DUPLEX, 3, CV_RGB(255, 255, 255));

    cv::imshow("test", img);
    cv::waitKey(1);
    std::system("pause");

    return 0;
}

Produces the following output:

However, I would like the text to be filled, instead of only having the borders visible.

---

According to the putText documentation, the lineType argument should be used to make the text filled.

Attempting to pass the cv::FILLED enum as the lineType argument to the putText call as such:

cv::putText(img, "TEST", cv::Point(50, 150), cv::FONT_HERSHEY_DUPLEX, 3, CV_RGB(255, 255, 255), 1, cv::FILLED);

results in no apparent changes to the output image:

I'm aware that I can simply make the thickness argument to the putText call higher to simulate a text fill, however I'm looking for a way to actually fill the text here, ideally without any text borders at all.

---

What is the proper way to draw filled text onto a cv::Mat image using OpenCV's C++ library?

Thanks for reading my post, any guidance is appreciated.