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>0)
scale +=step;
else if(value<0)
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：

1 #include <iostream>
2 #include <string>
3 #include <opencv2/opencv.hpp>
4
5 using namespace std;
6 using namespace cv;
7
8 float scale=1.0;
9
10 void zoomInAndOut(const float scale, const Mat srcImg, Mat &dstImg)
11 {
12     Mat M=Mat::eye(3,3,CV_32FC1);
13     int imgHeight=srcImg.rows;
14     int imgWidth=srcImg.cols;
15
16     uchar* pSrcData = (uchar*)srcImg.data;
17     uchar* pDstData = (uchar*)dstImg.data;
18
19     Point2f center(imgWidth / 2.0, imgHeight / 2.0);
20     //计算仿射矩阵
21     M.at<float>(0, 0) = scale;
22     M.at<float>(0, 2) = (1 - scale)*center.x;
23     M.at<float>(1, 1) = scale;
24     M.at<float>(1, 2) = (1 - scale)*center.y;
25
26     float a11 = M.at<float>(0, 0);
27     float a12 = M.at<float>(0, 1);
28     float a13 = M.at<float>(0, 2);
29     float a21 = M.at<float>(1, 0);
30     float a22 = M.at<float>(1, 1);
31     float a23 = M.at<float>(1, 2);
32     float a31 = M.at<float>(2, 0);
33     float a32 = M.at<float>(2, 1);
34     float a33 = M.at<float>(2, 2);
35
36     float bx = a11*a22 - a21*a12;
37     float by = a12*a21 - a11*a22;
38     if ( abs(bx) > 1e-3 && abs(by) > 1e-3)
39     {
40         bx = 1.0 / bx;
41         by = 1.0 / by;
42         float cx = a13*a22 - a23*a12;
43         float cy = a13*a21 - a23*a11;
44
45         for (int j =0; j < imgHeight; j++)
46         {
47             for (int i = 0; i < imgWidth; i++)
48             {
49                 float u = (a22*i - a12*j - cx) *bx;
50                 float v = (a21*i - a11*j - cy) *by;
51
52                 int u0 = floor(u);
53                 int v0 = floor(v);
54                 int u1 = floor(u0 + 1);
55                 int v1 = floor(v0 + 1);
56                 if (u0 >= 0 && v0 >= 0 && u1 < imgWidth && v1 < imgHeight)
57                 {
58                     float dx = u - u0;
59                     float dy = v - v0;
60                     float weight1 = (1 - dx)*(1 - dy);
61                     float weight2 = dx*(1 - dy);
62                     float weight3 = (1 - dx)*dy;
63                     float weight4 = dx*dy;
64
65                     for (int k=0; k<srcImg.channels(); k++)
66                     {
67                         pDstData[j*imgWidth * 3 + i * 3 + k] = weight1*pSrcData[v0*imgWidth * 3 + u0 * 3 + k] +
68                         weight2*pSrcData[v0*imgWidth * 3 + u1 * 3 + k] +
69                         weight3*pSrcData[v1*imgWidth * 3 + u0 * 3 + k] +
70                         weight4*pSrcData[v1*imgWidth * 3 + u1 * 3 + k];
71                     }
72                 }
73                 else
74                 {
75                    for (int k=0; k<srcImg.channels(); k++)
76                     {
77                         pDstData[j*imgWidth * 3 + i * 3 + k] = 0;
78                     }
79                 }
80             }
81         }
82     }
83 }
84
85 void onMouse(int event, int x, int y, int flags,  void* )
86 {
87     double value;
88     float step=0.02;
89     switch (event)
90     {
91     case CV_EVENT_MOUSEWHEEL:
92         value = getMouseWheelDelta(flags);
93         if (value>0)
94             scale +=step;
95         else if(value<0)
96             scale -=step;
97         break;
98     default:
99         break;
100     }
101 }
102
103 void main()
104 {
105     string imgPath="data/source_images/";
106     Mat srcImg = imread(imgPath+"moon.jpg");
107     pyrDown(srcImg, srcImg);
108     pyrDown(srcImg, srcImg);
109
110     Mat dstImg = srcImg.clone();
111     dstImg.setTo(0);
112
113     string windowName="showImg";
114     namedWindow(windowName);
115     imshow(windowName, srcImg);
116     waitKey(10);
117
118     setMouseCallback(windowName, onMouse, NULL);
119     float scaleMin=0.5;
120     float scaleMax=2;
121     while (true)
122     {
123         scale = (scale<scaleMin)? (scaleMin): scale;
124         scale = (scale>scaleMax)? (scaleMax): scale;
125         zoomInAndOut(scale, srcImg, dstImg);
126         imshow(windowName, dstImg);
127         waitKey(10);
128     }
129 }