OpenCV Overlay Text on Stream

opencv-overlay-text-on-stream.cpp

// Standard C++ Libraries
#include <iostream>
#include <sstream>
#include <string>
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>


using std::cout;
using std::endl;
using namespace cv;

#define BOXSIZE 50

string text = "Lorem Ipsum Dolor Sit Amet";

cv::Point getPt1(Mat& frame) {
    return cv::Point(frame.cols,frame.rows-BOXSIZE);
}

cv::Point getPt2(Mat& frame) {
    return cv::Point(0,frame.rows);
}


void drawRectangle (Mat& frame) {
    static cv::Point pt1(getPt1(frame));
    static cv::Point pt2(getPt2(frame));
    static cv::Scalar white(0,0,0);


    Mat overlay;
    frame.copyTo(overlay);

    cv::rectangle(
        overlay,
        pt1,
        pt2,
        white,
        CV_FILLED
    );
    double opacity = 0.6;
    addWeighted(overlay, opacity, frame, 1 - opacity, 0, frame);

}

void drawText(Mat& frame) {
    int baseline=0;
    const int fontFace = CV_FONT_HERSHEY_SIMPLEX;
    const double fontScale = 1;
    const int thickness = 1;

    static Size textSize = getTextSize(text, fontFace,
                                fontScale, thickness, &baseline);

    static Point textOrg((getPt1(frame).x - getPt2(frame).x)/2-textSize.width/2, (getPt1(frame).y + getPt2(frame).y)/2+textSize.height/2);

    putText(frame, text, textOrg, fontFace, fontScale,
            Scalar::all(255), thickness, 8);
}

int main(int argc, char *argv[])
{
    Mat frame;
    namedWindow("video", 1);

    VideoCapture cap(argv[1]);
    cap >> frame;

    while ( cap.isOpened() )
    {
        cap >> frame;
        if(frame.empty()) break;

        drawRectangle(frame);

        drawText(frame);

        imshow("video", frame);
        if(waitKey(30) >= 0) break;

    }

    return 0;
}