cv::waitKey doesn't respond to keypress (Bug #278)

Added by Kurt Konolige almost 15 years ago. Updated over 12 years ago.

Status:Done Start date:
Priority:Normal Due date:
Assignee:Gary Bradski % Done:

0%
Category:highgui-gui
Target version:-
Affected version: Operating System:
Difficulty: HW Platform:
Pull request:

Description

waitKey(1000) doesn't return after pressing a key (and <cr>).

Associated revisions

Revision e34aba60
Added by Andrey Kamaev about 12 years ago

Merge pull request #278 from taka-no-me:fix_build_jpeg9

Revision cf26748b
Added by Vadim Pisarevsky over 9 years ago

Merge pull request #278 from mshabunin:add_videoio_perf_data

History

#1
Updated by Gary Bradski almost 15 years ago

  • Status deleted (Open)

#2
Updated by Vadim Pisarevsky almost 15 years ago

The following sample works great on Ubuntu x64 9.10 with OpenCV built with GTK+ support.

===

#include "cv.h"
#include "highgui.h"
#include <stdio.h>

using namespace cv;

int main(int, char**) {
printf("press any key within 1 second\n");
namedWindow("test", 0);
int c = waitKey(1000);
printf("%d\n", c);
return 0;
}

===

I see 2 possible reasons of why you get this problem:

1. no window was created. waitKey() only works when there is at least one highgui window and the window is active.

2. key code of <Return> key is 10 ('\n'), while you might have checked for 13 instead.

If the problem is still there, please, reopen the ticket and, if possible, supply an example or more information.

  • Status set to Done
  • (deleted custom field) set to worksforme

#3
Updated by Vadim Pisarevsky almost 15 years ago

here is improved sample that proves that the real delay is shorter when a key is pressed:

===
#include "cv.h" // include standard OpenCV headers, same as before
#include "highgui.h"
#include <stdio.h>

using namespace cv; // all the new API is put into "cv" namespace. Export its content

int main(int, char**) {
printf("press any key within 1 second\n");
namedWindow("test", 0);
double t = (double)getTickCount();
int c = waitKey(1000);
t = (double)getTickCount() - t;
printf("delay = %g msec, key code = %d\n", t*1000./getTickFrequency(), c);
return 0;
} ===

#4
Updated by Anonymous almost 15 years ago

Please add info in the docs that the keypress has to take place when the highgui window is in focus.

#5
Updated by Vadim Pisarevsky almost 15 years ago

the note about the focus has been added in r3013

#6
Updated by Andrey Kamaev over 12 years ago

  • Category changed from highgui-images to highgui-gui

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