How to draw a rounded rectangle (rectangle with rounded corners) with OpenCV?

Question

How can I draw a rectangle with rounded corners in OpenCV? I know that the functions ellipse() and line() can be simply put together to draw it. I just wonder if someone has done it before and has put it in a proper function so I can use it? Ideally the corner radius is to calibrate in a parameter.

I searched a lot for that, but it seems no one had that problem before. If no one has such I function I will probably post my own solution here in a few days.

Answer 1

I realized, this is much easier that I thought. Here is my function. I hope it is helpful for someone.

/**
 * Draws a rectangle with rounded corners, the parameters are the same as in the OpenCV function @see rectangle();
 * @param cornerRadius A positive int value defining the radius of the round corners.
 * @author K
 */
void rounded_rectangle( Mat& src, Point topLeft, Point bottomRight, const Scalar lineColor, const int thickness, const int lineType , const int cornerRadius)
{
    /* corners:
     * p1 - p2
     * |     |
     * p4 - p3
     */
    Point p1 = topLeft;
    Point p2 = Point (bottomRight.x, topLeft.y);
    Point p3 = bottomRight;
    Point p4 = Point (topLeft.x, bottomRight.y);

    // draw straight lines
    line(src, Point (p1.x+cornerRadius,p1.y), Point (p2.x-cornerRadius,p2.y), lineColor, thickness, lineType);
    line(src, Point (p2.x,p2.y+cornerRadius), Point (p3.x,p3.y-cornerRadius), lineColor, thickness, lineType);
    line(src, Point (p4.x+cornerRadius,p4.y), Point (p3.x-cornerRadius,p3.y), lineColor, thickness, lineType);
    line(src, Point (p1.x,p1.y+cornerRadius), Point (p4.x,p4.y-cornerRadius), lineColor, thickness, lineType);

    // draw arcs
    ellipse( src, p1+Point(cornerRadius, cornerRadius), Size( cornerRadius, cornerRadius ), 180.0, 0, 90, lineColor, thickness, lineType );
    ellipse( src, p2+Point(-cornerRadius, cornerRadius), Size( cornerRadius, cornerRadius ), 270.0, 0, 90, lineColor, thickness, lineType );
    ellipse( src, p3+Point(-cornerRadius, -cornerRadius), Size( cornerRadius, cornerRadius ), 0.0, 0, 90, lineColor, thickness, lineType );
    ellipse( src, p4+Point(cornerRadius, -cornerRadius), Size( cornerRadius, cornerRadius ), 90.0, 0, 90, lineColor, thickness, lineType );
}