Question

So I’ve tried to write some pixels using MemoryImageSource and display it in a frame. Here’s the code:

public class ImageDraw extends JPanel {

Image img;

public void ImageDraw(){        
    //super();      
    int w=600;
    int h=400;

    int pixels[] = new int[w*h];    
    int i=0;    
    for(i=0;i<w*h;i++){
        //pixels[i++]=0;
        pixels[i]=255;      
    }   
    img = createImage(new MemoryImageSource(w,h,pixels,0,w));
}

 public void paint(Graphics g){     
    g.drawImage(img,  0, 0, this);
 }
}

and the main code

public class FuncTest {

  public static void main(String[] args) {

    JFrame frame = new JFrame("Display");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(600, 400);

    ImageDraw pan = new ImageDraw();
    frame.getContentPane().add(pan);
    frame.setVisible(true);
  }
}

It just displays an empty frame. Why? My aim is to learn how to draw pixel by pixel, so this is only a test image I was drawing to see whether it works.

Thanks.

Answer 1

There are two issues with your code. First

public void ImageDraw() {  ... }

is a method and not the constructor. The method is not called in your code at all. Change this line to

public ImageDraw() {  ... }

without the void to make it the default constructor.

Second you need to set the alpha-value of your pixel data:

pixels[i] = 255 + 0xFF000000;

And two more points:

• Please do not override paint(...) but paintComponent(...) instead.
• Do not set the size of the JFrame but override the component’s method getPreferredSize() and use frame.pack().