實現用按下滑鼠左鍵拖動時，在滑鼠經過的路徑上打上馬賽克。

馬賽克的原理是將影象中選中區域的畫素用這個選中區域中的某一畫素覆蓋。

為了不讓滑鼠重複經過影象中同一個的時候，選取不一樣的畫素，該程式將在輸入圖片的時候，就實現了全圖的馬賽克效果。而當滑鼠劃過的時候，程式只是將實現馬賽克的圖片的指定位置複製到顯示的影象中。效果類似於QQ截圖中的馬賽克。

#include <opencv2\core\core.hpp>
#include <opencv2\highgui\highgui.hpp>
#include <opencv2\imgproc\imgproc.hpp>
#include <iostream>

using namespace cv;
using namespace std;

Mat inputImage;
Mat inputImage_mosaic;
Mat inputImage_clone;

//馬賽克的大小
int neightbourhood = 20;

//記錄滑鼠的狀態，0為滑鼠左鍵未按下或彈起，1為滑鼠左鍵按下
int mouseStatus = 0;

void onMouse(int events, int x, int y, int flag, void* ustg);

//建立馬賽克圖片
void createMosaicImage(Mat inputMat, Mat& outputMat, int size);

//設定馬賽克區域
void setMosaic(Mat& inputMat, Rect rect);

int main(void){
	inputImage = imread("test2.jpg");
	inputImage_clone = inputImage.clone();
	createMosaicImage(inputImage, inputImage_mosaic, neightbourhood);

	namedWindow("showImage", 0);
	setMouseCallback("showImage", onMouse);

	waitKey();
	return 0;
}

void createMosaicImage(Mat inputMat, Mat& outputMat, int size){
	RNG rng;
	int height = inputMat.rows;
	int width = inputMat.cols;
	Mat padding;
	Mat tempMat;

	//為了方便後面的計算，將輸入的影象大小擴充到寬高都是size的倍數
	copyMakeBorder(inputMat, padding, 0, size - inputMat.rows % size, 0, size - inputMat.cols % size, BORDER_REPLICATE);
	tempMat = padding.clone();
	
	for (int row = 0; row < padding.rows; row += size){
		for (int col = 0; col < padding.cols; col += size){
			int rand_x = rng.uniform(0, size);
			int rand_y = rng.uniform(0, size);
			Rect rect = Rect(col, row, size, size);
			Mat roi = tempMat(rect);
			Scalar color = Scalar(padding.at<Vec3b>(row + rand_y, col + rand_x)[0], \
				padding.at<Vec3b>(row + rand_y, col + rand_x)[1], \
				padding.at<Vec3b>(row + rand_y, col + rand_x)[2]);
			roi.setTo(color);
		}
	}
	outputMat = tempMat(Rect(0, 0, width, height)).clone();
}

void setMosaic(Mat& inputMat, Rect rect){
	Mat roi = inputMat(rect);
	Mat tempRoi = inputImage_mosaic(rect);
	tempRoi.copyTo(roi);
}

void onMouse(int events, int x, int y, int flag, void* ustg){

	//當滑鼠移除圖片區域的時候，不做操作
	if (x < 0 || x > inputImage.cols || y < 0 || y > inputImage.rows){
		return;
	}

	//馬賽克塊的位置資訊
	int x_left, x_right, y_top, y_bottom;
	x - neightbourhood <= 0 ? x_left = 0 : x_left = x - neightbourhood;
	x + neightbourhood > inputImage.cols ? x_right = inputImage.cols: x_right = x + neightbourhood;
	y - neightbourhood <= 0 ? y_top = 0 : y_top = y - neightbourhood;
	y + neightbourhood > inputImage.rows ? y_bottom = inputImage.rows: y_bottom = y + neightbourhood;

	if (events == CV_EVENT_LBUTTONDOWN){
		mouseStatus = 1;
		setMosaic(inputImage_clone, Rect(x_left, y_top, x_right - x_left, y_bottom - y_top));
	}
	else if (events == CV_EVENT_MOUSEMOVE){
		if (mouseStatus == 1){
			setMosaic(inputImage_clone, Rect(x_left, y_top, x_right - x_left, y_bottom - y_top));
		}
		else{
			//nothing
		}
	}
	else if (events == CV_EVENT_LBUTTONUP){
		mouseStatus = 0;
	}
	else {
		//cout << "nothing" << endl;
	}
	imshow("showImage", inputImage_clone);
}