How to draw circle with even number diameter (for example, 100)

2

In ellipse() function you can define the bounding box of the ellipse (a RotatedRect), which can have any size (even real numbers).

For example a circle with diameter=100:

ellipse(image, RotatedRect(Point2f(100,100), Point2f(100,200), Point2f(200,200)), Scalar(0,0,255);