I am using opencv 4.60, and I am attempting the simplest of things, drawing on a black image.

This code, however, does not work:

cv::Mat img(600, 800, CV_8UC3, cv::Scalar::all(0));
cv::drawMarker(img, cv::Point(300,400), cv::Scalar(255, 255, 255), cv::MARKER_TILTED_CROSS, 20, 8);
cv::imshow("test", img);
cv::waitKey(1);

I just see a black image.
The same result with any drawing function, circle, line etc. all show me nothing.

I have compiled cv to the world lib, and have all relevant includes linked. Program compiles and runs perfectly, but does not draw.

What might be going on here?