问题描述：在测试目标跟踪算法时，需要选择不同区域作为目标，进行目标跟踪，测试目标跟踪的效果。
解决思路：
1.OpenCV中提供了鼠标交互控制，利用setMouseCallback()给固定的窗口设置鼠标回调函数。
2.在鼠标回调函数中，选择感兴趣区域。
代码实现如下，将感兴趣区域封装在MouseSelect类中，提供选择点和矩形框两种模式。
1 #pragma once
2 #ifndef __MOUSESELECT_H__
3 #define __MOUSESELECT_H__
4
5 #include <opencv2/opencv.hpp>
6 #include <iostream>
7
8 #define MAX_OBJECTS 10
9 using namespace cv;
10 using namespace std;
11 typedef struct MouseSelectParams
12 {
13 vector<Point> pts; //Points of selected
14 char *win_name;
15 Mat *image;
16 unsigned int mode; //1 Point,2 Rect
17 int n; // selected object number
18 }MouseSelectParams;
19
20 void on_mouse(int event,int x,int y,int flags,void *param);
21 class MouseSelect
22 {
23 public:
24 MouseSelect();
25 ~MouseSelect();
26
27 void select_rect(Mat &frame);
28 void select_point(Mat &frame);
29
30 vector<Point> vPoints;
31 vector<Rect> vRects;
32 unsigned int obj_selected;
33 private:
34 int get_rects(Mat &frame);
35 int get_points(Mat &frame);
36
37 };
38 #endif
1 #include "MouseSelect.h"
2
3 MouseSelectParams *g_mousep;
4 MouseSelect::MouseSelect() {}
5
6 MouseSelect::~MouseSelect() {}
7
8 void MouseSelect::select_rect(Mat &frame)
9 {
10 obj_selected = 0;
11 while(0 == obj_selected)
12 {
13 obj_selected = get_rects(frame);
14 if (obj_selected == 0)
15 {
16 cout<<"You haven't selected any rectangles. "<<endl;
17 }
18 }
19 }
20
21 void MouseSelect::select_point(Mat &frame)
22 {
23 obj_selected = 0;
24 while(0 == obj_selected)
25 {
26 obj_selected = get_points(frame);
27 if (obj_selected == 0)
28 {
29 cout<<"You haven't selected any points."<<endl;
30 }
31 }
32 }
33
34 int MouseSelect::get_rects(Mat &frame)
35 {
36 char *win_name = "Init Frame";
37 MouseSelectParams params;
38 params.win_name = win_name;
39 params.image = &frame;
40 params.n = 0;
41 params.mode = 2;
42 namedWindow(win_name,WINDOW_AUTOSIZE);
43 imshow(win_name,frame);
44
45 g_mousep = ¶ms;
46 setMouseCallback(win_name,on_mouse,0);
47 waitKey(0);
48 destroyWindow(win_name);
49
50 int x1,x2,y1,y2,w,h;
51 Rect rt;
52 Point pt1,pt2;
53 cout<<"Point Num: "<<params.pts.size()<<" Object Num: "<<params.n<<" Object Type: Rect."<<endl;
54 for(int i = 0;i < params.pts.size();i += 2)
55 {
56 pt1 = params.pts[i];
57 pt2 = params.pts[i + 1];
58 x1 = min(pt1.x,pt2.x);
59 x2 = max(pt1.x,pt2.x);
60 y1 = min(pt1.y,pt2.y);
61 y2 = max(pt1.y,pt2.y);
62 w = x2 - x1;
63 h = y2 - y1;
64 w = (w % 2)? w:w+1;
65 h = (h % 2)? h:h+1;
66 rt.x = x1;
67 rt.y = y1;
68 rt.width = w;
69 rt.height = h;
70 vRects.push_back(rt);
71 }
72 return params.n;
73 }
74
75 int MouseSelect::get_points(Mat &frame)
76 {
77 char *win_name = "Init Frame";
78 MouseSelectParams params;
79 params.win_name = win_name;
80 params.image = &frame;
81 params.n = 0;
82 params.mode = 1;
83
84 namedWindow(win_name,1);
85 imshow(win_name,frame);
86
87 g_mousep = ¶ms;
88 setMouseCallback(win_name,on_mouse,0);
89 waitKey(0);
90
91 destroyWindow(win_name);
92
93 cout<<"Point Num: "<<params.pts.size()<<" Object Num: "<<params.n<<" Object Type: Point."<<endl;
94 for (int i = 0;i < params.n;i++)
95 {
96 vPoints.push_back(params.pts[i]);
97 }
98 return params.n;
99 }
100
101 void on_mouse(int event,int x,int y,int flags,void *param)
102 {
103 int n;
104 static bool pressed = false;
105 static Point cur_pt;
106 static Point prev_pt;
107 /* on left button press, remember first corner of rectangle around object */
108 if (event == CV_EVENT_LBUTTONDOWN)
109 {
110 n = g_mousep->n;
111 if (n == MAX_OBJECTS)
112 {
113 return;
114 }
115 prev_pt.x = x;
116 prev_pt.y = y;
117 //cout<<prev_pt.x <<","<<prev_pt.y<<" "<<cur_pt.x<<","<<cur_pt.y<<endl;
118 pressed = true;
119 }
120 /* on left button up, finalise the rectangle and draw it in black */
121 else if(event == CV_EVENT_LBUTTONUP && pressed)
122 {
123 /* 1 == mode for selecting points */
124 if (1 == g_mousep->mode)
125 {
126 n = g_mousep->n;
127 if (n == MAX_OBJECTS)
128 {
129 return;
130 }
131 cur_pt.x = x;
132 cur_pt.y = y;
133 g_mousep->pts.push_back(cur_pt);
134 int radius = 3;
135 circle(*g_mousep->image,cur_pt,radius,CV_RGB(255,0,0));
136 imshow(g_mousep->win_name,*g_mousep->image);
137 pressed = false;
138 g_mousep->n++;
139 }
140 /* 2 == mode for selecting rectangles */
141 else if (2 == g_mousep->mode)
142 {
143 n = g_mousep->n;
144 if (n == MAX_OBJECTS)
145 {
146 return;
147 }
148 cur_pt.x = x;
149 cur_pt.y = y;
150 g_mousep->pts.push_back(prev_pt);
151 g_mousep->pts.push_back(cur_pt);
152 // cout<<prev_pt.x <<","<<prev_pt.y<<" "<<cur_pt.x<<","<<cur_pt.y<<endl;
153 rectangle(*g_mousep->image,prev_pt,cur_pt,CV_RGB(0,0,255));
154 imshow(g_mousep->win_name,*g_mousep->image);
155 pressed = false;
156 g_mousep->n++;
157 }
158 else if (3 == g_mousep->mode)
159 {
160 n = g_mousep->n;
161
162 }
163 }
164 else if (event == CV_EVENT_MOUSEMOVE && pressed && CV_EVENT_FLAG_LBUTTON)
165 {
166 if (2 == g_mousep->mode)
167 {
168 n = g_mousep->n;
169 if (n == MAX_OBJECTS)
170 {
171 return;
172 }
173 cur_pt.x = x;
174 cur_pt.y = y;
175 Mat tmp = (*g_mousep->image).clone();
176 //cout<<prev_pt.x <<","<<prev_pt.y<<" "<<cur_pt.x<<","<<cur_pt.y<<endl;
177 rectangle(tmp,prev_pt,cur_pt,CV_RGB(0,255,0));
178 imshow(g_mousep->win_name,tmp);
179 }
180 }
181 }
代码分析：
on_mouse()回调函数，对应于一个显示窗口。
在回调函数处理鼠标事件，要理解一个鼠标点击过程，会产生多个事件。
例如：鼠标左击，对应着CV_EVENT_LBUTTONDOWN和CV_EVENT_LBUTTONUP。
在选择矩形框区域时，CV_EVENT_LBUTTONDOWN记录一个对角点；CV_EVENT_MOUSEMOVE记录选对矩形框的中间过程，并显示出来，便于用户调整选择的区域；CV_EVENT_LBUTTONUP记录另一个对角点，CV_EVENT_LBUTTONUP响应后，完成一个矩形框的选择。
在选择点时，只需记录CV_EVENT_LBUTTONUP事件响应的坐标。