Save parts of screen to image file

hlhl

Hello,

I'm having an odd problem when trying to save parts of the screen in my window (i.e. a screenshot) to an image file. It works on the first call, but the subsequent calls simply write the first screenshot over again.

I'm coding a QGuiApplication, with QWindow. Somewhere in the QWindow-inherited class (outside any Qt/OpenGl rendering), I call:

m_context->screen()->grabWindow(winId(),x,y,w,h).save(QString("test.bmp"));

m_context is a QOpenGLContext, with the OpenGLSurface surface type.

Any ideas to why this only works on the first call (and then seems to "freeze" somehow)?

SGaist

Hi,

Can you provide a more complete example that shows the problem ?

hlhl

Here's a minimalist code snippet, MainWindow inherits QWindow:

@MainWindow::MainWindow(QWindow *parent) :
QWindow(parent),
m_context(0),
m_device(0),
{
setWidth(WINDOWRESX);
setHeight(WINDOWRESY);
setSurfaceType(QWindow::OpenGLSurface);
}

bool MainWindow::event(QEvent *event)
{
switch (event->type()) {
case QEvent::UpdateRequest:
render();
return true;
default:
return QWindow::event(event);
}
}

void MainWindow::exposeEvent(QExposeEvent *event)
{
Q_UNUSED(event);
if (isExposed())
startRender();
}

void MainWindow::render()
{
if (!m_device)
m_device = new QOpenGLPaintDevice;

m_device->setSize(size());
QPainter painter(m_device);

glClearColor(.75f,.75f,.75f,1.0f); // background colour
glViewport(0,0,width(),height());
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

painter.beginNativePainting(); // start OpenGL painting

openGL drawing

painter.endNativePainting();
render(&painter);

}

void MainWindow::render(QPainter *painter)
{
draw with painter
}

void MainWindow::startRender()
{
if (!isExposed())
return;

bool needsInitialize = false;

if (!m_context) {
    m_context = new QOpenGLContext(this);
    m_context->setFormat(requestedFormat());
    m_context->create();
    needsInitialize = true;
    initialize();
}

m_context->makeCurrent(this);
if (needsInitialize) {
    initializeOpenGLFunctions();
}

render();

m_context->swapBuffers(this);

}

void MainWindow::keyPressEvent(QKeyEvent *ev)
{
if(ev->key()==Qt::Key_S) { // save file
int x = 50, y = 50, w = 500, h = 500;
m_context->screen()->grabWindow(winId(),x,y,w,h).save(QString(“test.bmp”));
}
}@

SGaist

Shouldn't you make the context current before doing a grabWindow ?

hlhl

Nope, that didn't solve the problem; that is, the image that is being saved is still the first saved image, even if I delete the "old" image before I press S again. The edited keyPressEvent:

@void MainWindow::keyPressEvent(QKeyEvent *ev)
{
if(ev->key()==Qt::Key_S) { // save file
int x = 50, y = 50, w = 500, h = 500;
m_context->makeCurrent(this);
m_context->screen()->grabWindow(winId(),x,y,w,h).save(QString(“test.bmp”));
}
}@

SGaist

Did you try grabWidget ?

IamSumit

Try This,,
QString format = "bmp";
QString fileName="D:/mTest";
QPixmap::grabWidget(this).save(fileName, format.toAscii());