绘制缓冲图像 [英] Drawing on a buffered image

问题描述

我正在尝试绘制缓冲图像。我能够在框架上获得图片，但它似乎并没有在图像上绘制。如果我使用

I am trying to draw on a buffered image. I am able to get the picture on the frame but it doesnt seem to draw on the image. If I use

BufferedImage bufferedImage = new BufferedImage（1280,800，BufferedImage.TYPE_INT_RGB）;

然后它似乎绘制了字符串，但我想理想地绘制图像，因为我需要在图像上为项目绘制一些坐标。任何指导都将受到高度赞赏。请原谅不良缩进

then it seems to draw the string but I would like to ideally draw on the image as I need to plot some coordinates on the image for a project. Any guidance would be highly appreciated. Excuse the bad indentation

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class drawTest extends JPanel {

public void paint(Graphics g) {
   Image img = createImageWithText();
   g.drawImage(img, 20,20,this);
}

private Image createImageWithText(){
   BufferedImage bufferedImage = new BufferedImage(1280, 800,BufferedImage.TYPE_INT_RGB);
 //   BufferedImage bufferedImage = new BufferedImage()
  Graphics g = bufferedImage.getGraphics();

  try {
    bufferedImage = ImageIO.read(getClass().getResource("Unknown.jpg"));

  } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
  }
  g.drawString("Point is here", 20,20);


  return bufferedImage;
}

  public static void main(String[] args) {
    JFrame frame = new JFrame();
    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    double width = screenSize.getWidth();
    double height = screenSize.getHeight();
    frame.getContentPane().add(new drawTest());

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 // frame.setSize(200, 200);

    frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
    System.out.println(height + " " + width); 
    frame.setVisible(true);
 }
}

推荐答案

你正在创建两个 BufferedImage对象 - 一个是从中获取Graphics上下文并在其上绘制文本，另一个是通过ImageIO获取图片，不绘制文字。你返回后者，所以有意义的是图片没有新文本。

You're creating two BufferedImage objects -- one that you get the Graphics context from and draw text on, and the other that holds the picture obtained via ImageIO, that you don't draw text on. You return the latter, so it makes sense that the picture holds no new text.

    // BufferedImage Object ONE
    BufferedImage bufferedImage = new BufferedImage(1280, 800, BufferedImage.TYPE_INT_RGB); 
    Graphics g = bufferedImage.getGraphics();  // Graphics for the first object only

    try {
        // BufferedImage object TWO
        bufferedImage = ImageIO.read(getClass().getResource("Unknown.jpg"));

    } catch (IOException e) {
        e.printStackTrace();
    }

    // draw with the graphics context for the first object
    g.drawString("Point is here", 20, 20);

    return bufferedImage; // but return the second

解决方案：不要这样做，创建一个 BufferedImage，通过ImageIO说，获取其Graphics上下文，绘制它，处理图形完成后，返回它。

Solution: don't do this, create one BufferedImage only, say via ImageIO, get its Graphics context, draw with it, dispose the Graphics when done, and return it.

例如，

// have method accept the image path and 
// have it throw an exception if the path is bad
private Image createImageWithText2(String resourcePath) throws IOException {

    // create one and only one BufferedImage object. 
    // If this fails, the exception will bubble up the call chain
    BufferedImage bufferedImage = ImageIO.read(getClass().getResource(resourcePath));

    // get the Graphics context for this single BufferedImage object 
    Graphics g = bufferedImage.getGraphics();  

    g.drawString("Point is here", 20, 20);

    g.dispose();  // get rid of the Graphics context to save resources

    return bufferedImage;
}

您的代码存在其他问题：

Other problems with your code is here:

public void paint(Graphics g) {
   Image img = createImageWithText();
   g.drawImage(img, 20,20,this);
}

问题包括：

• 你正在覆盖错误的绘画方法。你应该覆盖paintComponent，而不是paint，实际上你的问题提到了paintComponent，所以我不确定你为什么要这样做。


• 你要覆盖绘画方法而不是调用超级方法，破坏了绘画链。


• 你在绘画方法中不必要地反复进行文件I / O，这种方法对GUI的感知响应性影响最大，所以你不想做的事情。读取一次中的图像将其存储到变量中，使用paintComponent中的变量，永远不要在绘制方法中执行文件I / O.


• 你会想要的学习和使用 Java命名约定。变量名都应以较低的字母开头，而类名以大写字母开头。学习这一点并遵循这一点将使我们能够更好地理解您的代码，并使您能够更好地理解他人的代码。

• You're overriding the wrong painting method. You should override paintComponent, not paint, and in fact your question mentions paintComponent, so I'm not sure why you're doing this.
• You're overriding a painting method but not calling the super's method, breaking the painting chain.
• You're doing file I/O unnecessarily repeatedly within a painting method, a method that has the greatest effect on the perceived responsiveness of your GUI, and so something you don't want to do. Read the image in once store it to a variable, use the variable within paintComponent, and never do file I/O within a painting method.
• You will want to learn and use Java naming conventions. Variable names should all begin with a lower letter while class names with an upper case letter. Learning this and following this will allow us to better understand your code, and would allow you to better understand the code of others.

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