《学习OpenCV》第四章课后题3-a

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题目说明：
创建一个程序读入并显示一幅图像。
a.允许用户在图像中选择一个矩形区域，然后通过按住鼠标按键画一个矩形。当鼠标键放开，高亮显示矩形框。注意，在内存中保留一个原始图像的副本，图像恢复为原始图像并重新开始绘矩形。

#include <highgui.h>#include <cv.h>/* 矩形框 */CvRect rect;bool draw = false;   // 标记是否在画IplImage* img;IplImage * temp;IplImage * original;void draw_rect(IplImage* img, CvRect rect){    cvRectangle( img,         cvPoint( rect.x, rect.y ),        cvPoint( rect.x + rect.width, rect.y + rect.height),        cvScalar( 0x00, 0x00, 0xff) );    printf("draw\n");}// 鼠标回调函数void my_mouse_callback( int event, int x, int y, int flags, void* param){    IplImage* image = (IplImage*) param;    switch( event )    {    case CV_EVENT_MOUSEMOVE:        {            if(draw)            {                rect.width = x - rect.x;                rect.height = y - rect.y;            }        }        break;    case CV_EVENT_LBUTTONDOWN:        {            draw = true;            rect = cvRect( x, y, 0, 0 );        }        break;    case CV_EVENT_LBUTTONUP:        {            draw = false;            if(rect.width < 0)            {                rect.x += rect.width;                rect.width *= -1;            }            if(rect.height < 0)            {                rect.y += rect.height;                rect.height *= -1;            }            // draw            draw_rect(image, rect);        }        break;        // 在右键按下时清除    case CV_EVENT_RBUTTONDOWN:        cvCopyImage(original, img);        printf("clear.\n");        break;    }}int main(){    img = cvLoadImage( "E:/shark.jpg", 1 );    rect = cvRect( -1, -1, 0, 0);    // 副本    temp = cvCloneImage( img );    original = cvCloneImage(img);    cvNamedWindow("draw rect");    cvSetMouseCallback("draw rect", my_mouse_callback, (void*)img);    while(1)    {        cvCopyImage(img, temp);        if(draw)        {            draw_rect( temp , rect );        }        cvShowImage( "draw rect", temp);        if(cvWaitKey(15) == 27)            break;    }    cvReleaseImage(&img);    cvReleaseImage(&temp);    cvReleaseImage(&original);    cvDestroyAllWindows();    return 0;}

引用：qdsclove的专栏
http://blog.csdn.net/stk_overflow/article/details/8760086

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