如何“正确”使用Java检测显示的DPI？ [英] How to "correctly" detect DPI of display with Java?
问题描述
我有以下应用程序绘制规则：
I have the following app that draws a rule :
public class Rule extends JComponent
{
public static final long serialVersionUID=26362862L;
// public static final int INCH=Toolkit.getDefaultToolkit().getScreenResolution();
public static final int INCH=(int)(Toolkit.getDefaultToolkit().getScreenResolution()*1.15); // Auto adjust this 1.15 ?
public static final int HORIZONTAL=0;
public static final int VERTICAL=1;
public static final int SIZE=35;
public int orientation;
public boolean isMetric;
private int increment;
private int units;
// private Color rule_color=new Color(0,135,235);
private Color rule_color=new Color(120,170,230);
static JFrame frame=new JFrame("Rule");
static Dimension screenSize=Toolkit.getDefaultToolkit().getScreenSize(); // 1600 x 1200 , 1024 x 768
static JPanel rulerPanel=new JPanel(new BorderLayout());
public Rule(int o,boolean m)
{
orientation=o;
isMetric=m;
setIncrementAndUnits();
}
public void setIsMetric(boolean isMetric)
{
this.isMetric=isMetric;
setIncrementAndUnits();
repaint();
}
private void setIncrementAndUnits()
{
if (isMetric)
{
units=(int)((double)INCH/(double)2.54); // dots per centimeter
increment=units;
}
else
{
units=INCH;
increment=units/2;
}
}
public boolean isMetric() { return this.isMetric; }
public int getIncrement() { return increment; }
public void setPreferredHeight(int ph) { setPreferredSize(new Dimension(SIZE,ph)); }
public void setPreferredWidth(int pw) { setPreferredSize(new Dimension(pw,SIZE)); }
public void setColor(Color color) { rule_color=color; }
public void paintComponent(Graphics g)
{
Rectangle drawHere=g.getClipBounds();
// Fill clipping area with blue-gray.
g.setColor(rule_color);
g.fillRect(drawHere.x,drawHere.y,drawHere.width,drawHere.height);
// Do the ruler labels in a small font that's black.
g.setFont(new Font("SansSerif",Font.PLAIN,10));
g.setColor(Color.black);
// Some vars we need.
int end=0;
int start=0;
int tickLength=0;
String text=null;
// Use clipping bounds to calculate first tick and last tick location.
if (orientation==HORIZONTAL)
{
start=(drawHere.x/increment)*increment;
end=(((drawHere.x+drawHere.width)/increment)+1)*increment;
}
else
{
start=(drawHere.y/increment)*increment;
end=(((drawHere.y+drawHere.height)/increment)+1)*increment;
}
// Make a special case of 0 to display the number within the rule and draw a units label.
if (start==0)
{
text=Integer.toString(0)+(isMetric?" cm":" in");
tickLength=10;
if (orientation==HORIZONTAL)
{
g.drawLine(0,SIZE-1,0,SIZE-tickLength-1);
g.drawString(text,2,21);
}
else
{
g.drawLine(SIZE-1,0,SIZE-tickLength-1,0);
g.drawString(text,9,10);
}
text=null;
start=increment;
}
// ticks and labels
for (int i=start;i<end;i+=increment)
{
if (i%units==0)
{
tickLength=10;
text=Integer.toString(i/units);
}
else
{
tickLength=5;
text=null;
}
if (tickLength!=0)
{
if (orientation==HORIZONTAL)
{
g.drawLine(i,SIZE-1,i,SIZE-tickLength-1);
if (text!=null) g.drawString(text,i-3,21);
}
else
{
g.drawLine(SIZE-1,i,SIZE-tickLength-1,i);
if (text!=null) g.drawString(text,9,i+3);
}
}
}
}
// Create the GUI and show it. For thread safety, this method should be invoked from the event-dispatching thread.
static void createAndShowGUI()
{
rulerPanel.setPreferredSize(new Dimension(570,78));
Rule cmView=new Rule(Rule.HORIZONTAL,true);
int H=35;
cmView.setPreferredHeight(H);
cmView.setColor(new Color(128,200,235));
JScrollPane cmScrollPane=new JScrollPane();
cmScrollPane.setViewportBorder(BorderFactory.createLineBorder(Color.black));
cmScrollPane.setColumnHeaderView(cmView);
rulerPanel.add("North",cmScrollPane);
Rule inchView=new Rule(Rule.HORIZONTAL,true);
inchView.setPreferredHeight(H);
inchView.setColor(new Color(168,200,235)); //238,238,238
inchView.setIsMetric(false);
JScrollPane inchScrollPane=new JScrollPane();
inchScrollPane.setViewportBorder(BorderFactory.createLineBorder(Color.black));
inchScrollPane.setColumnHeaderView(inchView);
rulerPanel.add("South",inchScrollPane);
frame.getContentPane().add(rulerPanel);
frame.addWindowListener(new WindowAdapter()
{
public void windowActivated(WindowEvent e) { }
public void windowClosed(WindowEvent e) { }
public void windowClosing(WindowEvent e) { System.exit(0); }
public void windowDeactivated(WindowEvent e) { }
public void windowDeiconified(WindowEvent e) { rulerPanel.repaint(); }
public void windowGainedFocus(WindowEvent e) { rulerPanel.repaint(); }
public void windowIconified(WindowEvent e) { }
public void windowLostFocus(WindowEvent e) { }
public void windowOpening(WindowEvent e) { rulerPanel.repaint(); }
public void windowOpened(WindowEvent e) { }
public void windowResized(WindowEvent e) { rulerPanel.repaint(); }
public void windowStateChanged(WindowEvent e) { rulerPanel.repaint(); }
});
frame.pack();
frame.setBounds((screenSize.width-rulerPanel.getWidth())/2,(screenSize.height-rulerPanel.getHeight())/2-19,rulerPanel.getWidth()+20,rulerPanel.getHeight()+38);
frame.setVisible(true);
}
public static void main(String[] args)
{
// Schedule a job for the event-dispatching thread : creating and showing this application's GUI.
SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } });
}
}
我的旧17和20工作正常显示，现在我注意到我的新27LCD，它是不准确的，所以我必须改变第4行更准确，不是Toolkit.getDefaultToolkit（）。getScreenResolution（）应该得到准确的DPI，为什么这是不正确的，因为我的应用程序可以在具有不同显示尺寸和DPI的其他机器上工作，如何自动调整我手动输入的1.15？
It worked fine on my old 17" and 20" displays, now I've noticed on my new 27" LCD, it's inaccurate, so I have to change the 4th line to be more accurate, isn't Toolkit.getDefaultToolkit().getScreenResolution() supposed to get the accurate DPI, why it's not correct, for my app to work on other machines with different display sizes and DPIs, how to automatically adjust the 1.15 I have manually put in ?
PS：不仅我的Java应用程序的DPI不准确，但是当我查看Windows 7上的其他几个应用程序（例如paint.exe或paint.net）时，它们的英寸和厘米也是正确的。您可以在您的计算机上试用它们。
PS : Not only my Java app's DPI is inaccurate, but also when I looked at several other apps on Windows 7 such as paint.exe or paint.net, their inch and cm are also in correct. You can try them on your machine.
推荐答案
驱动程序问题。
真正的DPI只有驱动程序才知道它通向操作系统，它将其报告给Java和其他应用程序。由于不仅Java具有错误的规模，它必须是驱动程序。
The real DPI is known only to driver, which reports it to the OS, which reports it to Java and other applications. Since not only Java has the wrong scale, it must be the driver.
这是古老的问题。许多图形应用程序都有一个全局设置屏幕DPI，用户可以根据实际监视器进行调整。
This is ages old problem. Many graphical applications have a global setting "screen DPI" where users can adjust for their actual monitor.
此外，由于你是用Java编写的，请记住一些操作系统无法告诉Java真正的DPI（因为他们不了解自己）。因此，对DPI配置设置的需求更加明确。
Besides, since you're writing in Java, keep in mind that some OSes have no means of telling Java the real DPI (because they don't know themselves). The need for DPI configuration setting is thus even more clear.
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