In windows this is very simple:
auto pixmap = qApp->screens().at(0)->grabWindow(QDesktopWidget().winId());
But grabWindow isn't working on linux. I try something like:
QScreen *screen = QGuiApplication::primaryScreen();
auto pixmap = QPixmap::grabWindow(0);
but with no good result.
QScreen *screen = QGuiApplication::primaryScreen();
QPixmap pixmap = screen->grabWindow(0);
Should work if screen is valid. You can refer to shootScreen method at Qt Screenshot Example
Related
I simplified the code and it is like this:
Mat mat = imread("xxx.jpg"); //Successfully read the image, confirmed by cvShowImage.
if (mat.empty())
{
qDebug() << "Couldn't load image";
return;
}
Mat cpy = mat.clone();
cvtColor(mat,cpy,CV_BGR2RGB);
QImage image(cpy.data, cpy.cols, cpy.rows, cpy.step, QImage::Format_RGB888);
try {
pm = QPixmap::fromImage(image); //crash line
} catch(std::exception const &ex){
qDebug()<<ex.what();
}
however the program just crashed without any debug log.. I've tried many images and the result is same. I tried to find the "stack trace" and it seems give segfault on this..
Had similar crash in QPixmap.fromImage. Found workaround by resizing image to a size aligned to 4 bytes
aligned = cv2.resize(img, (img.shape[1]//4*4, img.shape[0]//4*4), fx=0, fy=0, interpolation=cv2.INTER_NEAREST)
rgb = cv2.cvtColor(aligned, cv2.COLOR_BGR2RGB)
qimage = QImage(rgb.data, rgb.shape[1], rgb.shape[0], QImage.Format_RGB888)
pixmap = QPixmap.fromImage(qimage)
okay.. just change the conversion code to
QImage image(cpy.data, cpy.cols, cpy.rows, cpy.step, QImage::Format_RGB888);
image = image.rgbSwapped();
solved it. Actually I don't know why this fixed it. Maybe because I should use COLOR_BGR2RGB rather than CV_BGR2RGB..
Some background info about my issue. My goal is to optimize drawing of images coming from webcam, the images come as QVideoFrame and are currently loaded in to QImage and drawn from there. This solution works fine, but drawing QImage is very slow on X11. Drawing one image takes about 20ms which doesn't sound like much but when you do this for every frame this cut's the framerate of the camerafeed to half.
I did some research and testing, drawing QPixMaps in X11 can be done about 10 times faster than drawing QImages.
This is how the drawing process is done currently
if(mVFcurrentFrame.map(QAbstractVideoBuffer::ReadOnly))
{
QImage image(mVFcurrentFrame.bits(), mVFcurrentFrame.width(), mVFcurrentFrame.height(), mVFcurrentFrame.bytesPerLine(), imageFormat);
painter->drawImage(0,0,image); //Takes about 20ms
mVFcurrentFrame.unmap();
}
What i have tried so far:
Converting the QImage to QPixMap, this works but the conversion is as slow as painting the Qimage
Loading the QVideoFrame straight to QPixMap with QPixMap::loadFromData(), can't make it work.
So my question is, can i convert QVideoFrame straight to QPixMap and draw it instead of using QImage and how would you do the QVideoFrame to QPixmap conversion without using QImage in between?
I have tried using QPixMap::loadFromData() method to load the video frame but so far i have been unable to make it work.
If this isn't possible could i thread the QImage to QPixMap conversion or optimize the drawing in some other way?
This is my problem too.
camera frames are shown very slowly in QLabel.
my code is here:
QCamera *camera = new QCamera(this);
camera->setCaptureMode(QCamera::CaptureViewfinder);
QVideoProbe *videoProbe = new QVideoProbe(this);
bool ret = videoProbe->setSource(camera);
if (ret) {
connect(videoProbe, SIGNAL(videoFrameProbed(const QVideoFrame &)),
this, SLOT(present(const QVideoFrame &)));
}
camera->start();
...
...
bool MainWindow::present(const QVideoFrame &frame)
{
QVideoFrame cloneFrame(frame);
if(cloneFrame.map(QAbstractVideoBuffer::ReadOnly))
{
QImage img(
cloneFrame.size(), QImage::Format_ARGB32);
qt_convert_NV21_to_ARGB32(cloneFrame.bits(),
(quint32 *)img.bits(),
cloneFrame.width(),
cloneFrame.height());
label->setPixmap(QPixmap::fromImage(img));
cloneFrame.unmap();
}
return true;
}
I have a QGraphicsScene of big dimension for displaying a database content.
Part of the database is made of pictures that I place in the QGraphicsScene thanks to the method setPos() of a QGraphicsPixmapItem and this works fine with thousands of pictures.
In front of these pictures, I place QCheckboxes that are finally accessible through QGraphicsProxyWidgets. But QGraphicsProxyWidget::setPos(qreal x, qreal y) results in casting provided coordinates in signed short in the QGraphicsScene.
However, doing a QGraphicsProxyWidget::pos() returns correctly the original coordinates, even above 2^16.
Here is the code:
QCheckBox* checkbox = new QCheckBox("", this);
QWidget* dummyWidget = new QWidget; //used for having a transparent background
dummyWidget->setStyleSheet("background-color:transparent;"
"outline-color:transparent;"
"font-size: 8pt;");
QHBoxLayout* dummyLayout = new QHBoxLayout(dummyWidget);
dummyLayout->addWidget(checkbox);
QGraphicsProxyWidget* proxyWidget = scene.addWidget(dummyWidget);
proxyWidget->setPos(0, 120*i);
When 120*i is between 32769 and 65536, QChekBoxes don't show. For above values, QCheckBoxes are shown like if y = value - 65536.
I have tried many things without success, like
- proxyWidget->moveBy
- dummyWidget->move
- dummyWidget->setFixedSize(0, 240*i); checkbox->move(0, 120*i);
Any solution?
PS: The toolchain/cross-toolchain I depend from embeds QT4.8.1. for the desktop side.
I have no way to change that so upgrading to QT5.x is not an option.
You can use next trick:
void setNewPos(QGraphicsItem *item, QPointF pos)
{
item->resetTransform();
QTransform trans = item->transform();
item->setTransform(trans.translate(pos.x(), pos.y()));
}
Now, you can call this func:
QPushButton *btn = new QPushButton("Hello, people!");
QGraphicsProxyWidget *wdgItem = scene->addWidget(btn);
setNewPos(wdgItem, view->mapToScene(0,0)); // There's scenePos can have any coords
Trying to resize an image:
size_t targetWidth = funnyImage.get_width();
size_t targetHeight = funnyImage.get_height();
QString inputWidth = 400;
QString inputHeight = 900;
QImage *jpgImage = new QImage(targetWidth, targetHeight, QImage::Format_RGB32);
QImage small = jpgImage->scaled(inputWidth, inputHeight,Qt::KeepAspectRatio);
I get this error:
cpp:125: error: no matching function for call to 'QImage::scaled(QString&, QString&, Qt::AspectRatioMode)'
SOLUTION:
QImage small = jpgImage->scaled(inputWidth.toUInt(), inputHeight.toUint,Qt::KeepAspectRatio);
Posting it here, because the wonderful reflection made me think.
Solution:
QImage small = jpgImage->scaled( inputWidth.toUInt(), inputHeight.toUInt(), Qt::KeepAspectRatio);
Found this question when needing to scaling my window using Qt5.
QImage small = jpgImage->scaled(size());
works so much better than the proposed solution, as size() takes only in account the usable area. On the contrary, using height() and width() seems to not take into account the pixels used in the border/menu area.
Small version of my question
In a QGraphicsItem::paint() function I have a QGLFrameBufferObject. How do I get it on the paintdevice of the painter that is passed as an argument? (provided that the QGraphicsItem is in a scene that is being rendered by a QGraphicsView that has a QGLWidget as viewport => painter is using opengl engine)
QGraphicsItem::paint(QPainter* painter, ...)
{
QGLFramebufferObject fbo;
QPainter p(fbo);
... // Some painting code on the fbo
p.end();
// What now? How to get the fbo content drawn on the painter?
}
I have looked at the framebufferobject and pbuffer examples provided with Qt. There the fbo/pbuffer is drawn in a QGLWidget using custom opengl code. Is it possible to do the same thing within a paint() method of a QGraphicsItem and take the position of the QGraphisItem in the scene/view into account?
Big version of my question
Situation sketch
I have a QGraphicsScene. In it is an item that has a QGraphicsEffect (own implementation by overriding draw() from QGraphicsEffect). The scene is rendered by a QGraphicsView that has a QGLWidget as viewport.
In the QGraphicsEffect::draw(QPainter*) I have to generate some pixmap which I then want to draw using the painter provided (the painter has the QGLWidget as paintdevice). Constructing the pixmap is a combination of some draw calls and I want these to be done in hardware.
Simplified example: (I don't call sourcepixmap in my draw() method as it is not needed to demonstrate my problem)
class OwnGraphicsEffect: public QGraphicsEffect
{
virtual void draw(QPainter* painter);
}
void OwnGraphicsEffect::draw(QPainter* painter)
{
QRect rect(0,0,100,100);
QGLPixelBuffer pbuffer(rect.size(), QGLFormat(QGL::Rgba));
QPainter p(pbuffer);
p.fillRect(rect, Qt::transparent);
p.end();
painter->drawImage(QPoint(0,0), pbuffer->toImage(),rect);
}
Actual problem
My concerns are with the last line of my code: pbuffer->toImage(). I don't want to use this. I don't want to have a QImage conversion because of performance reasons. Is there a way to get a pixmap from my glpixelbuffer and then use painter->drawpixmap()?
I know I also can copy the pbuffer to a texture by using :
GLuint dynamicTexture = pbuffer.generateDynamicTexture();
pbuffer.updateDynamicTexture(dynamicTexture);
but I have no idea on how to get this texture onto the "painter".
Extending leemes' answer, here is a solution which can also handle multisample framebuffer objects.
First, if you want to draw on a QGLWidget, you can simply use the OpenGL commands
leemes suggested in his answer. Note that there is a ready-to-use drawTexture()
command available, which simplifies this code to the following:
void Widget::drawFBO(QPainter &painter, QGLFramebufferObject &fbo, QRect target)
{
painter.beginNativePainting();
drawTexture(target, fbo.texture());
painter.endNativePainting();
}
To draw multisample FBOs, you can convert them into non-multisample ones
using QGLFramebufferObject::blitFramebuffer (Note that not every hardware
/ driver combination supports this feature!):
if(fbo.format().samples() > 1)
{
QGLFramebufferObject texture(fbo.size()); // the non-multisampled fbo
QGLFramebufferObject::blitFramebuffer(
&texture, QRect(0, 0, fbo.width(), fbo.height()),
&fbo, QRect(0, 0, fbo.width(), fbo.height()));
drawTexture(targetRect, texture.texture());
}
else
drawTexture(targetRect, fbo.texture());
However, as far as I know, you can't draw using OpenGL commands on a non-OpenGL context.
For this, you first need to convert the framebuffer to a (software) image, like
a QImage using fbo.toImage() and draw this using your QPainter instead of the
fbo directly.
I think I figured it out. I use the QPainter::beginNativePainting() to mix OpenGL commands in a paintEvent:
void Widget::drawFBO(QPainter &painter, QGLFramebufferObject &fbo, QRect target)
{
painter.beginNativePainting();
glEnable(GL_TEXTURE_2D);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
glBindTexture(GL_TEXTURE_2D, fbo.texture());
glBegin(GL_QUADS);
glTexCoord2d(0.0,1.0); glVertex2d(target.left(), target.top());
glTexCoord2d(1.0,1.0); glVertex2d(target.right() + 1, target.top());
glTexCoord2d(1.0,0.0); glVertex2d(target.right() + 1, target.bottom() + 1);
glTexCoord2d(0.0,0.0); glVertex2d(target.left(), target.bottom() + 1);
glEnd();
painter.endNativePainting();
}
I hope this will also work in the paintEvent of a QGraphicsItem (where the QGraphicsView uses a QGLWidget as the viewport), since I only tested it in QGLWidget::paintEvent directly.
There is, however, still the following problem: I don't know how to paint a multisample framebuffer. The documentation of QGLFramebufferObject::texture() says:
If a multisample framebuffer object is used then the value returned from this function will be invalid.