Painting on Top of Image

Question

I'm trying to design an applet which simulates a radar screen. Although I'm a novice, I have managed to create the radar itself OK.
However, I would like the radar screen to "sit" on a "console", and I'm trying to use an image file as this background console. Although the image loads and displays AOK, I can't seem to draw the radar on top of it.
I have tried using both the Image and Graphics objects, for example:
public class radar extends Applet implements Runnable {
private Image img;
private Graphics buffer;
// First get the 'console' image... this works AOK....
buffer=getImage(getDocumentBase(),"ar200.png");
// Now I need to paint the radar screen on top of the
// image, but it applet won't work when I add...
buffer=img.getGraphics();
// I've used getGraphics separately - without preloading
// an image - to create the animated radar screen, which
// works AOK, for example:
public void paint(Graphics g) {
// Set the radar screen grid circles
buffer.setColor(Color.gray);
buffer.drawOval(0, 0, aW, aH);
buffer.drawOval(aW/2/4*1, aH/2/4*1, aW/4*3, aH/4*3);
buffer.drawOval(aW/2/4*2, aH/2/4*2, aW/4*2, aH/4*2);
buffer.drawOval(aW/2/4*3, aH/2/4*3, aW/4*1, aH/4*1);
.... etc
g.drawImage (img,0,0,this);
.... etc
So, I can display an imported "console" image file, OR draw and display an animated radar screen - but not both! I think it might be an issue with combining "on-screen" and "off-screen" painting, but I'm not at all sure.
If anyone could suggest the method to accomplish this, or point me to an online resource that I can study, I'd really appreciate it.
MTIA, Max

Answer 1

// Now I need to paint the radar screen on top of
of the
// image, but it applet won't work when I add...
buffer=img.getGraphics();
I am surprised that this line above compiled. I don't think you can load an image and get its graphics directly. You can get graphics of an image only if it is created by the component. What you need is to create an image (off-screen), draw everything (background image and radar) on it and copy it to on-screen.
On top of my head, here is a code for your applet to do this stuff:
Image off, back;
Graphics offG;
public void init()
// create your offscreeen image
off = createImage(getSize().width, getSize().height);
offG = off.getGraphics();<br>
// load your background image
back = getImage(getDocumentBase(),"ar200.png");
public void paint(Graphics g)
// draw everything to your off screen first
offG.drawImage(back, 0, 0, this);
// draw your radar on top of it.
offG.setColor(Color.gray);
//...other radar stuff
// copy your off screen to on screen now
g.drawImage(off, 0,0, this);
}ibosan