Qt在使用一些功能时需要用到DPI

Qt5.6已经可以自适应DPI与手动设置DPI

# 1. 使用MSVC
	// Get desktop dc
	HDC desktopDc = GetDC(NULL);
	// Get native resolution
	float horizontalDPI = GetDeviceCaps(desktopDc, LOGPIXELSX);
	float verticalDPI = GetDeviceCaps(desktopDc, LOGPIXELSY);
	
	int dpi = (horizontalDPI + verticalDPI) / 2; 
	int fontsize = 4 * dpi / 72; //8pt 144dpi is 4px 
	fontsize = fontsize > 8 ? fontsize : 8;
	QFont MenuFont("SimHei", fontsize);
	QApplication::setFont(MenuFont); 

# 2. 使用 MinGW
#include <QPaintDevice>  
//逻辑DPI
	int horizontalDPI = logicalDpiX(); 
	int verticalDPI  = logicalDpiY();  
//物理DPI （和逻辑DPI不一定相同）
	int horizontalDPI = physicalDpiX(); 
	int verticalDPI  = physicalDpiY(); 

# 3. 分辨率
#include <QDesktopWidget>
    int currentScreenWidth = QApplication::desktop()->width();
    int currentScreenHeight = QApplication::desktop()->height(); 
//或者 
    QDesktopWidget* desktopWidget = QApplication::desktop();
    //获取可用桌面大小
    QRect deskRect = desktopWidget->availableGeometry();
    //获取设备屏幕大小
    QRect screenRect = desktopWidget->screenGeometry()； 
    screenX = screenRect.width();
    screenY = screenRect.height();