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panel with image background and mouse draw

How can I use a image as background in a JPanel if the paint () method is already used for other purposes? (I'm tried to draw over a image in a panel).
Here is my code to draw as a pencil, but I don´t know how to add the image as background ?
#Override
public void paint(Graphics g) {
if (x >= 0 && y >= 0) {
g.setColor(Color.BLACK);
g.fillRect(x, y, 4, 4);
}
}
Thanks Diego

Suggestions:
Don't draw in the JPanel's paint(...) method but rather use it's paintComponent(...) method. There are several reasons for this, one being that if you use the paint(...) method, then you are also responsible for drawing the JPanel's borders and child components and at risk of messing up the rendering of these guys. Also you lose Swing's automatic double buffering.
First call the parent class's super method before calling any other code in the method. This will allow the JPanel to refresh its background and do any graphics housekeeping that may need to be done.
Next draw your background image using g.drawImage(...),
Then do your pencil drawing.

Hovercraft Full Of Eels gave good advice on one direction to take. Here is another.
Display the image in a (ImageIcon in a) JLabel.
When it comes time to paint:
Call createGraphics() on the BufferedImage to gain a Graphics2D object.
paint the lines or other visual elements to the graphics instance.
dispose of the graphics instance.
Call repaint() on the label.
E.G. as seen in this answer.

Print label of line with regard to line using Java graphics

I am doing a project in which I need to print the label/description of the line (drawn using graphics) with respect to orientation of the line.
Does anyone know how to do it?

Look to the Graphics2D methods such as rotate(), scale() & translate() - as well as the more general translate(AffineTransform) method.
See Transforming Shapes, Text, and Images in the Java tutorial for more details and working examples, especially of using an AffineTransform (which can concatenate scale, rotate, transform & shear operations).
You do not mention how you obtain the Graphics object. The Graphics object passed to Swing components in paintComponent(Graphics) will generally be a Graphics2D instance, and can be cast to one. To get a Graphics2D instance from a BufferedImage, call createGraphics().

Make a class called "Labelled line" and make it something like this
class LabeledLine {
private int x1, y1, x2, y2;
private String label;
public void drawOn(Graphics g) {
// need more features? thickness, etc? add it
g.drawLine(x1,y1,x2,y2);
// compute size of text, position of text, angle of text
// draw that text
}
}
A quick google for drawing angled text gave me a couple results, so that should be easy to do.

creating a pen tool, repainting issue - JAVA

I am trying to create a pen tool using mouse listeners:
public void mouseDragged(MouseEvent e) {
imageL.setCoordinates(originalPos, e.getPoint());
imageL.repaint();
originalPos = e.getPoint();
}
The paint function in the JLabel (imageL) receives two sets of points that allow drawing a line based upon the mouse drag. The only issue is that every time the drag is performed, the new layer does not contain the line drawn from the previous mouse drag. The paint function of the JLabel is as follows:
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2d = (Graphics2D)g;
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setColor(drawingColour);
g2d.drawLine(originCors.x,originCors.y,endCors.x,endCors.y);
}
So essentially my question is: How do I "add" the new line to the current layer?
any help would be great,
Thanks in advance

You want to draw in a JComponent's (and JLabel extends from JComponent) paintComponent method, not the paint method unless you plan to handle all the painting of the component's borders and children. Next, you may wish to have your drawing component hold an ArrayList of Point and add Points to this array list in the mouseDragged method. Then the paintComponent method can iterate through the list and paint all the lines. If all you want to do is paint one line, then have the painting JLabel hold both points in a class field.

Michael,
For a start, in swing (a JLabel is a swing component, as apposed to the older AWT library) the recommended practice is to override the paintComponent method (not the "paint" method). See The Java Tutorials: Custom Painting for the hows & whys of it.
If you want to custom-paint a-list-of-lines then you're going to have to do just that... not just the "new" one. One way around this is to "update" an image with each new line, and then custom-paint that... this is slightly quicker as you only "paint" the each line once, at the cost of using more memory (to maintain the "backgroun image")... but this technique lends itself to "double buffering", which avoids "that flickering" you get when you draw directly to the screen. See The Java Tutorials: Working with Images for the details. It's actually pretty straight forward.
I suggest you google for "java double buffering example" (avoid Rose India, it's full of crap).
Cheers. Keith.

How to resize an AWT Polygon in Java

Are there any in-built methods in the Java API which would allow me to resize a polygon?
Would it be quite a simple task to write my own method, or are there any others already made?

No, nothing built in, altho, when you draw the polygon, you can draw the polygon with a transformation matrix applied which could scale the polygon for you. (or rotate, skew, etc, etc).
see
Graphics2D.setTransform(transform);
Lets assume you are drawing the polygon in a JPanel, and you have overridden the paintComponent method of JPanel. Cast the Graphics object to a Graphics2D object, and use transforms to scale it as appropriate:
public void paintComponent(Graphic g) {
Graphics2D g2d = (Graphics2D) g;
AffineTransform saveTransform = g2d.getTransform();
try {
AffineTransform scaleMatrix = new AffineTransform();
scaleMatrix.scale(1.5, 1.5);
//or whatever you want
g2d.setTransform(scaleMatrix);
g2d.drawPolygon(myPolygon);
} finally {
g2d.setTransform(saveTransform);
}
}
Chances are you can set up the transformation matrix elsewhere (once) instead of each time in the paintComponent method, but i did here to show how to do it.
Also note, that this will move the polygon, you would probably want apply this to the transform:
add a translate to move the polygon to the origin
add a scale
add a translate to move the polygon back to the original position
in this way, the object doesn't move it just scales.

Yes, AffineTransform.createTransformedShape(Shape) will create a transformed copy of any Shape (which may be a Polygon or Path2D.)

Cannot get image to move where I want it to (and update continuously)?

I'm Basically programming a simple game engine but I'm having problems with my sprites/images not appearing when they should... or at all!
I'll try and keep this as simple as possible. I have a Sprite, GameEngine and Display class. In the gameloop, I have a method that sets the new position of my Sprite (so it just sets the x and y variables). Next I call a transform method which does the following:
public void transform() {
affineTransform.setToIdentity();
affineTransform.translate(x, y);
}
Following that, I then call a draw method in the Sprite:
public void draw() {
graphics2D.drawImage(image, affineTransform, jFrame);
}
Finally, in my thread I then call repaint() on the JFrame (the Display class). My paint method for that class is as follows:
public void paint(Graphics g) {
g.drawImage(backbuffer, insets.left, insets.top, this);
}
But nothing is appearing, apart from a black screen!
I'm also getting confused between Graphics g, and Graphics2D and when to use either. (The overridden paint method uses Graphics g). For the record, I do have a Graphics2D variable in the class that is created by calling backbuffer.createGraphics();
Another thing that is confusing me is this AffineTransform... I've read the documentation but I'm still utterly confused on how and when to use it - and what exactly it seems to do. Is there any explanation in relatively simple terms?
Surely this should be working... am I missing something out here?

To answer part of your question:
From the Graphics2D JavaDoc
This Graphics2D class extends the Graphics class to provide more sophisticated control over geometry, coordinate transformations, color management, and text layout. This is the fundamental class for rendering 2-dimensional shapes, text and images on the Java(tm) platform.
Essentially, with Graphics2D you can do much more than you can with Graphics. And with a Sun JVM 1.5+, it should be safe to cast the Graphics object you get in paint() to Graphics2D
I just noticed this: For the record, I do have a Graphics2D variable in the class that is created by calling backbuffer.createGraphics();
You should make sure you're not drawing on a Graphics[2D] canvas (I'll use this term to refer to the drawable area that the Graphics[2D] object provides) that you later throw away. If you're drawing your image on a separate canvas, you should ensure that you then draw that image onto your actual display canvas.
I don't really have a good explanation of AffineTransform but maybe these will help?
http://www.javalobby.org/java/forums/t19387.html
https://secure.wikimedia.org/wikipedia/en/wiki/Affine_transformation
From Wikipedia - In general, an affine transformation is composed of linear transformations (rotation, scaling or shear) and a translation (or "shift"). Several linear transformations can be combined into a single one. Basically, you use this class to perform operations such as rotation, translation, zoom etc.