dll.h

#ifndef _DLL_H_
#define _DLL_H_

#if BUILDING_DLL
#define DLLIMPORT __declspec(dllexport)
#else
#define DLLIMPORT __declspec(dllimport)
#endif
#include <bits/stdc++.h>
#include <io.h>
#include <windows.h>
#include <direct.h>
#include <opencv2/opencv.hpp>

using namespace cv;
using namespace std;

void overlayImages(const Mat &background, const Mat &foreground, Mat &output, int x, int y){
    if (background.cols < x + foreground.cols || background.rows < y + foreground.rows){
        output = foreground.clone();
        cv::Rect roi(x, y, background.cols, background.rows);
        roi &= cv::Rect(0, 0, foreground.cols, foreground.rows);
        cv::Mat roi_output = output(roi);
        cv::Mat roi_background = background(cv::Rect(0, 0, roi.width, roi.height));
        for (int i = 0; i < roi.height; ++i){
            for (int j = 0; j < roi.width; ++j){
                cv::Vec4b pixel_background = roi_background.at<cv::Vec4b>(i, j);
                cv::Vec4b &pixel_output = roi_output.at<cv::Vec4b>(i, j);
                double alpha_background = pixel_background[3] / 255.0;
                double alpha_foreground = 1.0 - alpha_background;
                for (int k = 0; k < 3; ++k){
                    pixel_output[k] = static_cast<uchar>(alpha_background * pixel_background[k] + alpha_foreground * pixel_output[k]);
                }
                pixel_output[3] = static_cast<uchar>((alpha_background * 255) + (alpha_foreground * pixel_output[3]));
            }
        }
        Mat temp=output;
        for (int y = 0; y < foreground.rows; ++y) {
            for (int x = 0; x < foreground.cols; ++x) {
                cv::Vec4b pixel1 = foreground.at<cv::Vec4b>(y, x);
                cv::Vec4b pixel2 = temp.at<cv::Vec4b>(y, x);
                if (pixel1[3] > 0) {
                    output.at<cv::Vec4b>(y, x) = pixel1;
                } else {
                    output.at<cv::Vec4b>(y, x) = pixel2;
                }
            }
        }
    }
    else{
        output = background.clone();
        cv::Rect roi(x, y, foreground.cols, foreground.rows);
        roi &= cv::Rect(0, 0, background.cols, background.rows);
        cv::Mat roi_output = output(roi);
        cv::Mat roi_foreground = foreground(cv::Rect(0, 0, roi.width, roi.height));
        for (int i = 0; i < roi.height; ++i){
            for (int j = 0; j < roi.width; ++j){
                cv::Vec4b pixel_foreground = roi_foreground.at<cv::Vec4b>(i, j);
                cv::Vec4b &pixel_output = roi_output.at<cv::Vec4b>(i, j);
                double alpha_foreground = pixel_foreground[3] / 255.0;
                double alpha_background = 1.0 - alpha_foreground;
                for (int k = 0; k < 3; ++k){
                    pixel_output[k] = static_cast<uchar>(alpha_foreground * pixel_foreground[k] + alpha_background * pixel_output[k]);
                }
                pixel_output[3] = static_cast<uchar>((alpha_foreground * 255) + (alpha_background * pixel_output[3]));
            }
        }
    }
}

extern "C" __declspec(dllexport) void imgset(string path1, string path2, string outpath, int x, int y);
#endif