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  1. Qt
  2. QTBUG-73075

Timeout when get image data from clipboard

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    • Platform/s:
      All

      Description

      Copy a big image to clipboard, I can't get it in other application. The following code can reproduce this problem:

       

      // a.cpp
      #include <QGuiApplication>
      #include <QImage>
      #include <QClipboard>
      int main(int argc, char *argv[])
      
      { 
          QGuiApplication a(argc, argv);
          // If you load a more complex image, the size of the image pair can be reduced a lot. I tried using a jpg image with a size of 5613x3744, and I can get the same result.
          QImage image(20000, 20000, QImage::Format_ARGB32);
          image.fill(Qt::red);
          a.clipboard()->setImage(image);
          return a.exec();
       }
      

       

       

      // b.cpp
      #include <QGuiApplication> 
      #include <QImage> 
      #include <QClipboard>
      int main(int argc, char *argv[])
      {
          QGuiApplication a(argc, argv);
          QClipboard *b = a.clipboard();
          QObject::connect(b, &QClipboard::dataChanged, [b] { 
              QElapsedTimer et; 
              et.start();
              const QMimeData *data = b->mimeData();
              if (data->hasFormat("image/png")) { 
                   qint64 start = et.elapsed();
                   qDebug() << data->data("image/png").length();
                   qDebug() << et.elapsed() - start;
             }
      
         });
         return a.exec();
      }
      
      1. First start the application "b.cpp"
      2. Second start the applicatioin "a.cpp"

      I get the messages in "b.cpp":

      0
      5012
      

      Not only did not get the image data, and the application "b.cpp" was also blocked for 5 seconds.

      I found that the QXcbClipboard code has the "clipboard_timeout":
      https://github.com/qt/qtbase/blob/dev/src/plugins/platforms/xcb/qxcbclipboard.cpp#L222

      And
      https://github.com/qt/qtbase/blob/dev/src/plugins/platforms/xcb/qxcbclipboard.cpp#L901
      I guess "b.cpp" didn't get the image data because it waited for the clipboard event to time out. And see:  https://github.com/qt/qtbase/blob/dev/src/gui/kernel/qinternalmimedata.cpp#L222
      Because the image size is large, it takes a lot of time for "a.cpp" to encode QImage data into PNG format. Can provide encoding speed by reducing the compression ratio of PNG.

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        For Gerrit Dashboard: QTBUG-73075
        # Subject Branch Project Status CR V

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            Assignee:
            zccrs chen zhang
            Reporter:
            zccrs chen zhang
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              Dates

              Created:
              Updated:

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