Capture Qt widget as an image file

I'm working with QGLWidget (Qt widget for OpenGL) and want to be able to capture the screen 开发者_如何学Pythondisplayed by the widget as JPEG files. How can I achieve this? Is there a function that return what is currently displayed on the widget as an image?

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Normally with OpenGL, you would read from the framebuffer using the glReadPixels() function. This will put the framebuffer contents into a buffer that you have allocated. You then need a function that will convert this to JPEG.

However, as you are using QGLWidget, you can use its grabFrameBuffer() method to obtain the frame buffer contents as a QImage object. This is probably the better way to go. You can grab the framebuffer contents, then use QImage::save() to save to a file.

If you move to Qt 5's QOpenGLWidget, you'll find it has a similar grabFrameBuffer() method.

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QImage img(mywidget.size());
QPainter painter(&img);
mywidget.render(&painter);
img.save("/some/file.jpg");

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Here is the simplest way to save widget as an image, working on Qt 5:

QString file = QFileDialog::getSaveFileName(this, "Save as...", "name", "PNG (*.png);; BMP (*.bmp);;TIFF (*.tiff *.tif);; JPEG (*.jpg *.jpeg)");
ui->myWidget->grab().save(file);

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Why not use the very simple incantation QPixmap::grabWindow( m_widget->winId() ).save( "/some/file.jpg" )

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QPixmap pixmap = QPixmap::grabWidget( &widget );
pixmap.save("widget.png");

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Improved version of @roop's answer.

QPixmap pixmap(mywidget.sizeHint());
QPainter painter(&pixmap);
mywidget.render(&painter);
pixmap.save("/some/file.png");

Changes:

• using pixmap instead of image
• using size hint instead of size
• saving to lossless PNG instead of JPEG

Note that for this to work, the widget does NOT need to be displayed on screen.