OpenCV鼠标滑轮事件

鼠标的滑轮事件实现图像的缩放很方便，具体在回调函数中如下写：

其中scale可以在外部定义为全局变量，通过响应CV_EVENT_MOUSEWHEEL滑轮事件获取Scale的具体值。

获取Scale值需要关注两个问题，滑轮滑动的方向和滑动量的大小。滑动方向通过getMouseWheelDelta（flags）获取，当返回值＞0时，表示向前滑动；当返回值＜0时，表示向后滑动。滑动量根据滑动方向自行设置相应的滑动步长即可。

void onMouse(int event, int x, int y, int flags,  void* )

{

    double value;

    float step=0.02;

    switch (event)

    {

    case CV_EVENT_MOUSEWHEEL:

        value = getMouseWheelDelta(flags);

        if (value>)

            scale +=step;

        else if(value<)

            scale -=step;

        break;

    default:

        break;

    }

}

下面是简单编写的滑动滑轮实现图像的缩放操作代码：

 #include <iostream>

 #include <string>

 #include <opencv2/opencv.hpp>

 using namespace std;

 using namespace cv;

 float scale=1.0;

 void zoomInAndOut(const float scale, const Mat srcImg, Mat &dstImg)

 {

     Mat M=Mat::eye(,,CV_32FC1);

     int imgHeight=srcImg.rows;

     int imgWidth=srcImg.cols;

     uchar* pSrcData = (uchar*)srcImg.data;

     uchar* pDstData = (uchar*)dstImg.data;

     Point2f center(imgWidth / 2.0, imgHeight / 2.0);

     //计算仿射矩阵

     M.at<float>(, ) = scale;

     M.at<float>(, ) = ( - scale)*center.x;

     M.at<float>(, ) = scale;

     M.at<float>(, ) = ( - scale)*center.y;

     float a11 = M.at<float>(, );

     float a12 = M.at<float>(, );

     float a13 = M.at<float>(, );

     float a21 = M.at<float>(, );

     float a22 = M.at<float>(, );

     float a23 = M.at<float>(, );

     float a31 = M.at<float>(, );

     float a32 = M.at<float>(, );

     float a33 = M.at<float>(, );

     float bx = a11*a22 - a21*a12;

     float by = a12*a21 - a11*a22;

     if ( abs(bx) > 1e- && abs(by) > 1e-)

     {

         bx = 1.0 / bx;

         by = 1.0 / by;

         float cx = a13*a22 - a23*a12;

         float cy = a13*a21 - a23*a11;

         for (int j =; j < imgHeight; j++)

         {

             for (int i = ; i < imgWidth; i++)

             {

                 float u = (a22*i - a12*j - cx) *bx;

                 float v = (a21*i - a11*j - cy) *by;

                 int u0 = floor(u);

                 int v0 = floor(v);

                 int u1 = floor(u0 + );

                 int v1 = floor(v0 + );

                 if (u0 >=  && v0 >=  && u1 < imgWidth && v1 < imgHeight)

                 {

                     float dx = u - u0;

                     float dy = v - v0;

                     float weight1 = ( - dx)*( - dy);

                     float weight2 = dx*( - dy);

                     float weight3 = ( - dx)*dy;

                     float weight4 = dx*dy;

                     for (int k=; k<srcImg.channels(); k++)

                     {

                         pDstData[j*imgWidth *  + i *  + k] = weight1*pSrcData[v0*imgWidth *  + u0 *  + k] +

                         weight2*pSrcData[v0*imgWidth *  + u1 *  + k] +

                         weight3*pSrcData[v1*imgWidth *  + u0 *  + k] +

                         weight4*pSrcData[v1*imgWidth *  + u1 *  + k];

                     }

                 }

                 else

                 {

                    for (int k=; k<srcImg.channels(); k++)

                     {

                         pDstData[j*imgWidth *  + i *  + k] = ;

                     }

                 }

             }

         }

     }

 }

 void onMouse(int event, int x, int y, int flags,  void* )

 {

     double value;

     float step=0.02;

     switch (event)

     {

     case CV_EVENT_MOUSEWHEEL:

         value = getMouseWheelDelta(flags);

         if (value>)

             scale +=step;

         else if(value<)

             scale -=step;

         break;

     default:

         break;

     }

 }

 void main()

 {

     string imgPath="data/source_images/";

     Mat srcImg = imread(imgPath+"moon.jpg");

     pyrDown(srcImg, srcImg);

     pyrDown(srcImg, srcImg);

     Mat dstImg = srcImg.clone();

     dstImg.setTo();

     string windowName="showImg";

     namedWindow(windowName);

     imshow(windowName, srcImg);

     waitKey();

     setMouseCallback(windowName, onMouse, NULL);

     float scaleMin=0.5;

     float scaleMax=;

     while (true)

     {

         scale = (scale<scaleMin)? (scaleMin): scale;

         scale = (scale>scaleMax)? (scaleMax): scale;

         zoomInAndOut(scale, srcImg, dstImg);

         imshow(windowName, dstImg);

         waitKey();

     }

 }