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How can I paint an image from BufferStrategy to Png file?

I've created a Java program that generates snowflakes and I'd like to save the image created as a .png file once the program finishes drawing.
I've searched on Internet, but I've found only programs using BufferedImage, while I use a BufferStrategy, so I don't know exactly where to start.
The draw method in my program uses a BufferStrategy to create the Graphics component.
For example, to draw a simple line the method is:
bs = display.getCanvas().getBufferStrategy();
if (bs == null) {
display.getCanvas().createBufferStrategy(3);
return;
}
g = bs.getDrawGraphics();
g.clearRect(0, 0, width, height);
g.setColor(Color.BLACK);
g.drawLine(0, 0, 50, 50);
What I would like is to get an exact copy of what has been drawn on the screen by the program to be saved as a .png image.
Hope you can help me.

Why not take a screenshot and then past it onto MS paint or some other(and better) image editing software like Photoshop or fire alpaca? That should solve your problem.

The common denominator between BufferedStrategy and BufferedImage is Graphics, so you want to write a paint routine so that you can simply pass a reference of Graphics to it
public void render(Graphics g) {
g.clearRect(0, 0, width, height);
g.setColor(Color.BLACK);
g.drawLine(0, 0, 50, 50);
}
Then you can pass what ever context you want.
BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_RGB);
Graphics2D g2d = img.createGraphics();
render(g2d);
g2d.dispose();
Then you can use ImageIO.write to write the image to disk. See Writing/Saving an Image for more details

Graphics.drawImage() consumes a lot of memory drawing an int[] image

I have an ImageViewComponent that extends JComponent. This component is added to a JPanel that is added to a JFrame. From another class I regularly update the int[] image field of ImageViewComponent from another class.
The problem is that this process eats up a lot of memory. It even consumes so much memory (+/- 130 MB after a few seconds according to JProfiler, and eventually it surpasses 1GB) that the entire program undergoes a 'lag spike' during garbage collection (the lag in the program happens at the same time that the memory is cleared).
This is the code of ImageViewComponent:
public class ImageViewComponent extends JComponent {
private int image_width, image_height, updateInterval, updateCounter;
private int[] imageArray;
private BufferedImage currentDisplayedImage;
private Image scaledDisplayedImage;
/**
* #param width The width of this component
* #param height The height of this component
* #param ui The higher, the less frequent the image will be updated
*/
public ImageViewComponent(int width, int height, int ui) {
setPreferredSize(new Dimension(width, height));
this.updateInterval = ui;
this.updateCounter = 0;
this.currentDisplayedImage = null;
this.scaledDisplayedImage = null;
}
public void setImage(int[] image, int width, int height) {
this.imageArray = image;
this.image_width = width;
this.image_height = height;
}
#Override
public void paint(Graphics g) {
super.paint(g);
if (image_width == 0 || image_height == 0)
return;
else if (updateCounter != updateInterval && currentDisplayedImage != null) {
g.drawImage(scaledDisplayedImage, 0, 0, this);
updateCounter++;
return;
}
this.currentDisplayedImage = new BufferedImage(image_width, image_height, BufferedImage.TYPE_INT_RGB);
this.currentDisplayedImage.setRGB(0, 0, image_width, image_height, this.imageArray, 0, image_width);
this.scaledDisplayedImage = this.currentDisplayedImage.getScaledInstance(this.getPreferredSize().width,
this.getPreferredSize().height, BufferedImage.SCALE_DEFAULT);
g.drawImage(scaledDisplayedImage, 0, 0, this);
// reset update counter
updateCounter = 0;
}
}
JProfiler states that 70% of the program its active memory is allocated in this class, 50% is in Graphics.drawImage while 20% is in BufferedImage initialization.
I have tried fixing it by putting the line this.currentDisplayedImage = new BufferedImage(image_width, image_height, BufferedImage.TYPE_INT_RGB) in `setImage' and have it only set it once with a boolean flag but this makes the drawn image turn completely black for short amounts of time once in a while, nor does it fix the memory problem.
I also tried this suggestion, which didn't work either.
How can I fix this memory issue?

There are several issues with the code. Some refer to performance, others to style or best practices, and others (at least potentially) refer to memory consumption.
Performance: The getScaledInstance method is distressingly slow. See https://stackoverflow.com/a/32278737/3182664 and others for better alternatives
Style: It's imageWidth, not image_width
Best practices: For a JComponent, you usually, you override paintComponent and not paint
Memory consumption: That's the main point...:
As MadProgrammer already pointed out: Do things as rarely as possible. The role and purpose of this updateCounter is not entirely clear. I think that the responsibility for updating the image less frequently should be in the class that uses your component - particularly, in the class that calls updateImage (which should simply be done less often). Maintaining this in the paint method is not very reliable.
In your current code, it seems like the currentDisplayedImage is (despite its name) neither displayed nor used in any other way. It may, however, be a good idea to keep it: It will be needed to be filled with the int[] data, and as a source for the scaled image that might have to be created.
One possible implementation of your class might look as follows:
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.geom.AffineTransform;
import java.awt.image.AffineTransformOp;
import java.awt.image.BufferedImage;
import javax.swing.JComponent;
public class ImageViewComponent extends JComponent {
private int updateInterval, updateCounter;
private BufferedImage fullImage;
private BufferedImage displayedImage;
/**
* #param width The width of this component
* #param height The height of this component
* #param ui The higher, the less frequent the image will be updated
*/
public ImageViewComponent(int width, int height, int ui) {
setPreferredSize(new Dimension(width, height));
this.updateInterval = ui;
this.updateCounter = 0;
this.fullImage = null;
this.displayedImage =
new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
}
public void setImage(int[] image, int width, int height) {
// Note: The updateInvervall/updateCounter stuff COULD
// probably also be done here...
if (fullImage == null ||
fullImage.getWidth() != width ||
fullImage.getHeight() != height)
{
fullImage = new BufferedImage(
width, height, BufferedImage.TYPE_INT_RGB);
}
fullImage.setRGB(0, 0, width, height, image, 0, width);
scaleImage(fullImage, displayedImage);
repaint();
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(displayedImage, 0, 0, this);
}
private static BufferedImage scaleImage(
BufferedImage input, BufferedImage output)
{
double scaleX = (double) output.getWidth() / input.getWidth();
double scaleY = (double) output.getHeight() / input.getHeight();
AffineTransform affineTransform =
AffineTransform.getScaleInstance(scaleX, scaleY);
AffineTransformOp affineTransformOp =
new AffineTransformOp(affineTransform, null);
return affineTransformOp.filter(input, output);
}
}
but note that this does not do this "updateInterval" handling, for the reason mentioned above.
And a side note: Maybe you don't even have to scale the image. If your intention is to have the image always being displayed at the size of the component, then you can simply do
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
// Draw the FULL image, which, regardless of its size (!)
// is here painted to just fill this component:
g.drawImage(fullImage, 0, 0, getWidth(), getHeight(), null);
}
Usually, drawing a scaled image like this is pretty fast. But depending on many factors, separating the step of scaling and painting the image, like you did, may also be a reasonable option.

Copy the contents of a JPanel onto a BufferedImage

On the first time through, I insert BufferedImages from a list onto my JPanel from my extended class:
#Override
protected void paintComponent(Graphics g){
super.paintComponent(g);
if (controlWhichImage == 1){
for (BufferedImage eachImage : docList){
g.drawImage(eachImage, 0,inty,imageWidth,imageHeight,null);
intx += eachImage.getWidth();
inty += eachImage.getHeight() * zoomAdd;
}
if (intx >= this.getWidth() || inty >= this.getHeight()){
inty = 0;
}
The next time I want to copy the contents of the JPanel to a BufferedImage:
public void recordImage(){
controlWhichImage = 2;
this.createdImage = new BufferedImage(this.getWidth(), this.getHeight(), BufferedImage.TYPE_INT_ARGB);
Image halfWay = this.createImage(this.getWidth(), this.getHeight());
//now cast it from Image to bufferedImage
this.createdImage = (BufferedImage) halfWay;
}
And then, take the modified BufferedImage and draw it back onto the JPanel:
if (controlWhichImage == 2){
g.drawImage(this.createdImage,0,inty,this.getWidth(),this.getHeight(),null);
}
This second time I get a blank panel.
I hope this is clear, any help gratefully received.
Sorry for my poor explanation. I will try to make myself clearer.
On each iteration the user is able to draw on the image in the Jpanel.
What I want to do is copy the user altered jpanel into a buffered image which will then be in the Jpanel to be edited again by the user.
This continues until the user selects print.
So apart from the code that I have put here are the controls for drawing by the user, at the moment I am struggling with putting the initial updated image from the original Jpanel into a bufferedImage and then back to the JPanel.
Hope this makes it somewhat clearer

To draw to a BufferedImage, you would do something similar to what you already do in your paintComponent method, but with your BufferedImage. Perhaps a method like:
// imgW and imgH are the width and height of the desired ultimate image
public BufferedImage combineImages(List<BufferedImage> docList, int imgW, int imgH) {
// first create the main image that you want to draw to
BufferedImage mainImg = new BufferedImage(imgW, imgH, BufferedImage.TYPE_INT_ARGB);
// get its Graphics context
Graphics g = mainImage.getGraphics();
int intx = 0;
int inty = 0;
// draw your List of images onto this main image however you want to do this
for (BufferedImage eachImage : docList){
g.drawImage(eachImage, 0,inty,imageWidth,imageHeight,null);
intx += eachImage.getWidth();
inty += eachImage.getHeight() * zoomAdd;
}
}
// anything else that you need to do
g.dispose(); // dispose of this graphics context to save resources
return mainImg;
}
You could then store the image returned into a varaible and then draw it in your JPanel if desired, or write it to disk.
If this doesn't answer your question, then again you'll want to tell more and show us your MCVE.

I have painted a panel but when the program starts panel shows with delay. what should I do?

I have painted a panel but when the program starts panel shows with delay. what should I do?
Toolkit kit = Toolkit.getDefaultToolkit();
Image img = kit.getImage(ResourceLoader.class.getResource("wood3.jpg"));
#Override
public void paintComponent(Graphics g) {
super.paintComponents(g);
int width = getWidth();
int height = getHeight();
Graphics2D graphics = (Graphics2D) g;
graphics.setStroke(new BasicStroke(1));
graphics.drawImage(img, 0, 0, width, height, null, null);
this.updateUI();
repaint();
}

You are calling repaint() inside paintComponent(Graphics g) function: you understand that it is going to be a recursive painting-stack(request) call. Try printing a string inside your code and set your eyes on the console.
Use a Thread to read the image and let the swing run in EDT using SwingUtilities.invokeLater(Runnable). That way you won't have to await your application for the image to load.
As MadProgrammer has suggested, use Graphics.drawImage(x, y, width, height, ImageObserver) function. Try to set this as the Observer instead of null. #AndrewThompson had an example to show the usecase of ImageObserver. i have forgot the link however :P

Java2D negative position can not be displayed, move origin to bottom left

I am trying to draw lines on coordinates system in Graphics2D. However, I find out that the part on line in negative area can not be shown. Is there anyway I can make the lines in negative area be seen?
Also, is there anyway I can convert direct of y-axis from downward to upward?
Graphics2D g2 = (Graphics2D) g;
g2.scale(1, -1);
g2.translate(0, -HEIGHT);
Can't work. Object disappears.
Thanks!

Ah, you are using the HEIGHT attribute. You should be using getHeight().
The code below produces this screenshot (g2.drawLine(0, 0, 100, 100)):
Code:
public static void main(String[] args) throws Exception {
JFrame frame = new JFrame("Test");
frame.add(new JComponent() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g.create();
{
g2.translate(0, getHeight() - 1);
g2.scale(1, -1);
g2.drawLine(0, 0, 100, 100);
}
g2.dispose();
}
});
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(400, 300);
frame.setVisible(true);
}

As far as I understand Java2D you can't use negative coordinates. You always operate in the so-called "User Space" in Java2D. The translates coordinates of your position in "Device Space" might be negative, but this is invisible to you in Java. See also Java2D Tutorial - Coordinates and Graphics2D API.
You might be able to achieve what you want by subclassing Graphics2D and doing the those translation yourself.