OpenCV鼠标画图例程，鼠标绘制矩形

鼠标画矩形：

// An example program in which the
// user can draw boxes on the screen.
//
/* License:
   Oct. 3, 2008
   Right to use this code in any way you want without warrenty, support or any guarentee of it working.

   BOOK: It would be nice if you cited it:
   Learning OpenCV: Computer Vision with the OpenCV Library
     by Gary Bradski and Adrian Kaehler
     Published by O'Reilly Media, October 3, 2008

   AVAILABLE AT:
     http://www.amazon.com/Learning-OpenCV-Computer-Vision-Library/dp/0596516134
     Or: http://oreilly.com/catalog/9780596516130/
     ISBN-10: 0596516134 or: ISBN-13: 978-0596516130    

   OTHER OPENCV SITES:
   * The source code is on sourceforge at:
     http://sourceforge.net/projects/opencvlibrary/
   * The OpenCV wiki page (As of Oct 1, 2008 this is down for changing over servers, but should come back):
     http://opencvlibrary.sourceforge.net/
   * An active user group is at:
     http://tech.groups.yahoo.com/group/OpenCV/
   * The minutes of weekly OpenCV development meetings are at:
     http://pr.willowgarage.com/wiki/OpenCV
*/
#include <cv.h>
#include <highgui.h>
#pragma comment(lib,"opencv_core2410d.lib")
#pragma comment(lib,"opencv_highgui2410d.lib")

// Define our callback which we will install for
// mouse events.
//
void my_mouse_callback( int event, int x, int y, int flags, void* param );

CvRect box;
bool drawing_box = false;

// A litte subroutine to draw a box onto an image
//
void draw_box( IplImage* img, CvRect rect )
{
  cvRectangle
	(
    img,
    cvPoint(box.x,box.y),
    cvPoint(box.x+box.width,box.y+box.height),
    cvScalar(0xff,0x00,0x00)    /* red */
	);
}

int main( int argc, char* argv[] )
{

  box = cvRect(-1,-1,0,0);

  IplImage* image = cvCreateImage(
    cvSize(200,200),
    IPL_DEPTH_8U,
    3
  );
  cvZero( image );
  IplImage* temp = cvCloneImage( image );

  cvNamedWindow( "Box Example" );

  // Here is the crucial moment that we actually install
  // the callback.  Note that we set the value ‘param’ to
  // be the image we are working with so that the callback
  // will have the image to edit.
  //
  cvSetMouseCallback(
    "Box Example",
    my_mouse_callback,
    (void*) image
  );

  // The main program loop.  Here we copy the working image
  // to the ‘temp’ image, and if the user is drawing, then
  // put the currently contemplated box onto that temp image.
  // display the temp image, and wait 15ms for a keystroke,
  // then repeat…
  //
  while( 1 ) {

    cvCopyImage( image, temp );
    if( drawing_box ) draw_box( temp, box );
    cvShowImage( "Box Example", temp );

    if( cvWaitKey( 15 )==27 ) break;
  }

  // Be tidy
  //
  cvReleaseImage( &image );
  cvReleaseImage( &temp );
  cvDestroyWindow( "Box Example" );
}

// This is our mouse callback.  If the user
// presses the left button, we start a box.
// when the user releases that button, then we
// add the box to the current image.  When the
// mouse is dragged (with the button down) we
// resize the box.
//
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( drawing_box ) {
        box.width  = x-box.x;
        box.height = y-box.y;
      }
    }
    break;
    case CV_EVENT_LBUTTONDOWN: {
      drawing_box = true;
      box = cvRect( x, y, 0, 0 );
    }
    break;
    case CV_EVENT_LBUTTONUP: {
      drawing_box = false;
      if( box.width<0  ) {
        box.x+=box.width;
        box.width *=-1;
      }
      if( box.height<0 ) {
        box.y+=box.height;
        box.height*=-1;
      }
      draw_box( image, box );
    }
    break;
  }
}