问题
I'km working in Qt, i need help to get the physical size of the screen (monitor),
In Qt one can get a QDesktopWidget
from QApplication
, I mean:
QDesktopWidget *mydesk = QApplication::desktop();
The QDesktopwidget
has some methods to get the resolution in pixels and some to get the the size in milimethers:
mydesk-> widthMM(); mydesk->heightMM();
However, this does not correspond to the physical size, when I measure my screen with a ruler, there is a considerable difference.
Also one can get the DPI measurement and calculate the size of the screen:
mydesk->physicalDpiX(); mydesk->physicalDpiY();
double Winches = (double)mydesk.width() / (double)mydesk.physicalDpiX();
double Hinches = (double)mydesk.Height() / (double)mydesk.physicalDpiY();
where mydesk.width()
and mydesk.height()
give the size in pixels(resolution)
However the measurement is also wrong and very close to mydesk.widthMM()
and mydesk.heightMM()
Also I have triyed mydesk.logicalDpiX()
and it has similar results.
回答1:
Here is my (quick and dirty) example. It seems to work for me and I hope it works for you. I'm assuming you can take care of main.cpp on your own. I did this on a MacBook Air 11.6" and substituted a picture of a dime for the USA icon included with OS X:
#ifndef WINDOW_H
#define WINDOW_H
#include <QtGui>
class Window : public QWidget
{
Q_OBJECT
public:
QWidget *canvas;
QSlider *slider;
QPixmap pixmap;
private:
qreal zoom;
qreal pixels;
qreal px_width;
qreal px_height;
qreal mm_width;
qreal mm_height;
public:
Window();
void paintEvent(QPaintEvent *);
public slots:
void setZoom(int);
};
Window::Window()
{
QHBoxLayout *layout = new QHBoxLayout;
canvas = new QWidget;
slider = new QSlider;
slider->setMinimum(0);
slider->setMaximum(100);
slider->setValue(50);
layout->addWidget(canvas);
layout->addWidget(slider);
this->setLayout(layout);
if(!pixmap.load(":/resources/USA.gif"))
{
qDebug() << "Fatal error: Unable to load image";
exit(1);
}
QObject::connect(slider, SIGNAL(valueChanged(int)), SLOT(setZoom(int)));
}
void Window::paintEvent(QPaintEvent *event)
{
QPainter paint;
paint.begin(this);
paint.scale(zoom, zoom);
paint.drawPixmap(0,0, pixmap);
paint.end();
}
void Window::setZoom(int new_zoom)
{
zoom = (qreal)(50+new_zoom) /50;
pixels = pixmap.width() * zoom;
QDesktopWidget desk;
px_width = desk.width() / pixels;
px_height = desk.height() / pixels;
mm_width = px_width * 17.9;
mm_height = px_height * 17.9;
qDebug() << "Zoom: " << zoom;
qDebug() << "desk.widthMM:" << desk.widthMM();
qDebug() << "px_width: " << px_width;
qDebug() << "px_height: " << px_height;
qDebug() << "mm_width: " << mm_width;
qDebug() << "mm_height: " << mm_height;
this->repaint();
}
#include "moc_window.cpp"
#endif // WINDOW_H
回答2:
The following method worked for me to get accurate physical size of my screen in mm.
QSizeF screenSize = QGuiApplication::primaryScreen()->physicalSize();
However, in Qt documentation I found the following sentence:
Depending on what information the underlying system provides the value might not be entirely accurate.
So it might not work for your system.
来源:https://stackoverflow.com/questions/8594969/get-physical-screen-size-in-qt