We Keep Coding

Java (re)painting mechanism [duplicate]

In java awt or swing when you want to change painting of some component you usually have to override the method paint(Graphics g) (in awt) or paintComponent(Graphics g) (in swing).
This is usually (maybe allways - I'm not sure) done when you are creating the component for example:
JPanel jPanel = new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
//... my implementation of paint, some transfromations, rotation, etc
}
};
Imagine that you have container of components which could for example consists of some JLabels, some JTextFields, some image. Which will be all put on one component.
By container I mean you have some list or map with ids or some similar structure in which are all components you will put on one JFrame.
The question is if I can change the painting method after creating with all of the components which are in this list in the moment when all of them are already created. For example I want do the rotation action (rotate), which is defined in Graphisc2D, with all of them.
So basicaly what I want is that I throught the list of componets I have and say:
"All of you (components) which are in the list will be rotated by some angle". Is that possible? If yes how?
Edit:
This is my not correctly working solution:
graphicalDisplayPanel = new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g2d = (Graphics2D) g;
g2d.rotate(Math.PI, anchorx, anchory);
}
#Override
public void paintChildren(Graphics g) {
super.paintChildren(g);
Graphics2D g2d2 = (Graphics2D) g;
g2d2.rotate(Math.PI, anchorx, anchory);
}
};
JFrame jFrame = JFrame();
// ... setting dimension, position, visible etc for JFrame, it works correctly nonrotated
jFrame.setContentPane(graphicalDisplayPanel);

I have not tested this, but it seems like it would work. A JComponent's paint() method calls:
paintComponent(co);
paintBorder(co);
paintChildren(co);
where co is a Graphics object. In theory you create an image, retrieve the graphics object and then pass that into paintChildren(). you will have to call paintComponent() and paintBorder() yourself, if you do this. Then, just rotate the image and draw it into your component. You may have to crop the image or resize your component accordingly for this to work. It might look something like this:
BufferedImage myImage;
#Override
public void paint(Graphics g){
myImage = new BufferedImage(getWidth(), getHeight(), BufferedImage.TRANSLUCENT);
//using a transparent BufferedImage might not be efficient in your case
Graphics myGraphics = myImage.getGraphics();
super.paintComponent(g);
super.paintBorder(g);
super.paintChildren(myGraphics);
//rotation code here
// ...
//draw children onto your component
g.drawImage(myImage, 0, 0,getWidth(), getHeight(), null);
}
I hope I didn't make any mistakes, please let me know if this works.

So basicaly what I want is that I throught the list of componets I have and say: "All of you (components) which are in the list will be rotated by some angle".
If you want to rotate panel and therefore all the components on the panel as a single using then you need to do the custom painting in the paintComponent() method.
If you want to rotate, for example, individual images that each have a different angle of rotation then you can again do this in the paintComponent(...) method and change the angle for each component.
Or, in this second case you can use the Rotated Icon class. In this case the Icon is just added to a JLabel. Then you can change the degrees of rotation and repaint the label, so there is no custom painting (except in the Icon itself).

Background image for a jPanel not working

I am new to making GUIs so I decided to try the the windows builder for eclipse, and while great I do have some doubts. I have been searching but I cannot seen to find a good way to add a background image to my "menu". For example I tried this:
public Menu() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(50, 50, 300, 250); //Dimensiones
contentPane = new JPanel() { //Imagen de Fondo
public void paintComponent(Graphics g) {
Image img = Toolkit.getDefaultToolkit().getImage(
Menu.class.getResource("/imgs/rotom.jpg"));
g.drawImage(img, 0, 0, this.getWidth(), this.getHeight(), this);
}
};
And adding the following classes:
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
But to no avail the window remains with its dull grey color, so far my code is just the standard one WindowsBuilder cooks for you plus 4 buttons but I doubt they're of importance here. Shouldn't the code I added override the paintComponent() method of the jPanel and draw the image in it?
The class for the menu is in a package within my project and the image is within a imgs package is within the same project as well.
Thanks a lot in advance.

A simple method, if you're not interested in resizing the background image or applying any effects is to use a JLabel...
BufferedImage bg = ImageIO.read(Menu.class.getResource("/imgs/rotom.jpg"));
JLabel label = new JLabel(new ImageIcon(bg));
setContentPane(label);
setLayout(...);
There are limitations to this approach (beyond scaling), in that the preferred size of the label will always be that of the image and never take into account it's content. This is both good and bad.
The other approach, which you seem to be using, is to use a specialised component
public class BackgroundPane extends JPanel {
private BufferedImage img;
public BackgroundPane(BufferedImage img) {
this.img = img;
}
#Override
public Dimension getPreferredSize() {
return img == null ? super.getPreferredSize() : new Dimension(img.getWidth(), img.getHeight());
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(img, 0, 0, this);
}
}
You should avoid trying to perform any task in the paintComponent method which may take time to complete as paintComponent may be called often and usually in quick succession....
Getting the image to scale when the component is resized is an entire question into of it self, for some ideas, you could take a look at...
Java: maintaining aspect ratio of JPanel background image
Java: JPanel background not scaling
Quality of Image after resize very low -- Java
Reading/Loading images
Oh, and, you should avoid extending directly from top level containers, like JFrame, they reduce the reusability for your components and lock you into a single container

JButton Transparency on an BufferedImage

I have a Problem:
I'm rendering a BufferedImage in a JFrame. Then i add a JButton to the same frame.
when i try to make the button transparent, the button becomes transparent, but disregarding its actual position, its always transparent like it is stuck in the top left corner of the frame.
I testet some different methods to make the button transparent, always with the same result.
any ideas?
thanks
public class TestPanel extends JPanel {
public TestPanel(){
JButton foo = new JButton("test");
foo.setBackground(new Color(0, 0, 0, 0));
foo.setBounds(20, 100, 300, 50);
this.add(foo);
}
public void paint(Graphics g){
Graphics2D g2 = (Graphics2D) g;
g2.drawImage(ImageFactory.getImg(), 0, 0, null); //get a BufferedImage
g2.dispose();
}
}

I see several problems, even if I'm not sure on which of them cause your problem.I try to list them in order:
Your TestPanel doesn't specify a LayoutManager (I hope you are specifying it somewhere else in your code).
You are extending a JPanel without call super paintComponent method (don't use paint). You should do this before anything else in your paintComponent method:
public void paintComponent(Graphics g){
super.paintComponent(g);
}
remove the dispose method call. You must not destroy your graphic object.
EDIT:
this is a problem:
foo.setBounds(20, 100, 300, 50);
you are trying to explicitly set the bounds of your JButton. You shouldn't do that. If you are using a LayoutManager it probably ignore this directive. If you are using a null layout this could be a problem too.

Several problems
it's wrong to override paint, instead override paintComponent
the button has a fully transparent background but returns true for opaque, thus fooling the paint mechanism
it's wrong to dispose the Graphics passed in as parameter
working code (Edit: accidentally removed the transparent color-setting line, fixed)
public TestPanel(){
JButton foo = new JButton("test");
foo.setBackground(new Color(0, 0, 0, 0));
foo.setOpaque(false);
foo.setBorder(BorderFactory.createLineBorder(Color.RED));
this.add(foo);
}
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.drawImage(ImageFactory.getImg(), 0, 0, null); //get a BufferedImage
// g2.dispose();
}
As others already noted: LayoutManagers are a must in Swing/AWT - not using them makes the ui code brittle and hard to maintain.

setBound() will work only if you have set your layout to null. Your code does not say anything like that.
Now, the default layout manager of JPanel is FlowLayout. By default, this layout manager will arrange your components from left to right then top to bottom.
Now, to make your code work as expected. Add this line inside your constructor: setLayout(null).
But remember, setting the layout to null is a very poor practice.
Also, the points Heisenbug has mentioned are very worthy. Try to follow them.

How to set a transparent background of JPanel?

Can JPanels background be set to transparent?
My frame is has two JPanels:
Image Panel and
Feature Panel.
Feature Panel is overlapping Image Panel.
The Image Panel is working as a background and it loads image from a remote URL.
On Feature Panel I want to draw shapes. Now Image Panel cannot be seen due to Feature Panel's background color.
I need to make Feature Panel background transparent while still drawing its shapes and I want Image Panel to be visible (since it is doing tiling and cache function of images).
I'm using two JPanel's, because I need to seperate the image and shape drawing .
Is there a way the overlapping Jpanel have a transparent background?

Calling setOpaque(false) on the upper JPanel should work.
From your comment, it sounds like Swing painting may be broken somewhere -
First - you probably wanted to override paintComponent() rather than paint() in whatever component you have paint() overridden in.
Second - when you do override paintComponent(), you'll first want to call super.paintComponent() first to do all the default Swing painting stuff (of which honoring setOpaque() is one).
Example -
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class TwoPanels {
public static void main(String[] args) {
JPanel p = new JPanel();
// setting layout to null so we can make panels overlap
p.setLayout(null);
CirclePanel topPanel = new CirclePanel();
// drawing should be in blue
topPanel.setForeground(Color.blue);
// background should be black, except it's not opaque, so
// background will not be drawn
topPanel.setBackground(Color.black);
// set opaque to false - background not drawn
topPanel.setOpaque(false);
topPanel.setBounds(50, 50, 100, 100);
// add topPanel - components paint in order added,
// so add topPanel first
p.add(topPanel);
CirclePanel bottomPanel = new CirclePanel();
// drawing in green
bottomPanel.setForeground(Color.green);
// background in cyan
bottomPanel.setBackground(Color.cyan);
// and it will show this time, because opaque is true
bottomPanel.setOpaque(true);
bottomPanel.setBounds(30, 30, 100, 100);
// add bottomPanel last...
p.add(bottomPanel);
// frame handling code...
JFrame f = new JFrame("Two Panels");
f.setContentPane(p);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setSize(300, 300);
f.setLocationRelativeTo(null);
f.setVisible(true);
}
// Panel with a circle drawn on it.
private static class CirclePanel extends JPanel {
// This is Swing, so override paint*Component* - not paint
protected void paintComponent(Graphics g) {
// call super.paintComponent to get default Swing
// painting behavior (opaque honored, etc.)
super.paintComponent(g);
int x = 10;
int y = 10;
int width = getWidth() - 20;
int height = getHeight() - 20;
g.drawArc(x, y, width, height, 0, 360);
}
}
}

Alternatively, consider The Glass Pane, discussed in the article How to Use Root Panes. You could draw your "Feature" content in the glass pane's paintComponent() method.
Addendum: Working with the GlassPaneDemo, I added an image:
//Set up the content pane, where the "main GUI" lives.
frame.add(changeButton, BorderLayout.SOUTH);
frame.add(new JLabel(new ImageIcon("img.jpg")), BorderLayout.CENTER);
and altered the glass pane's paintComponent() method:
protected void paintComponent(Graphics g) {
if (point != null) {
Graphics2D g2d = (Graphics2D) g;
g2d.setRenderingHint(
RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setComposite(AlphaComposite.getInstance(
AlphaComposite.SRC_OVER, 0.3f));
g2d.setColor(Color.yellow);
g2d.fillOval(point.x, point.y, 120, 60);
}
}
As noted here, Swing components must honor the opaque property; in this variation, the ImageIcon completely fills the BorderLayout.CENTER of the frame's default layout.

In my particular case it was easier to do this:
panel.setOpaque(true);
panel.setBackground(new Color(0,0,0,0,)): // any color with alpha 0 (in this case the color is black

(Feature Panel).setOpaque(false);
Hope this helps.

To set transparent you can set opaque of panel to false like
JPanel panel = new JPanel();
panel.setOpaque(false);
But to make it transculent use alpha property of color attribute like
JPanel panel = new JPanel();
panel.setBackground(new Color(0,0,0,125));
where last parameter of Color is for alpha and alpha value ranges between 0 and 255 where 0 is full transparent and 255 is fully opaque

public void paintComponent (Graphics g)
{
((Graphics2D) g).setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER,0.0f)); // draw transparent background
super.paintComponent(g);
((Graphics2D) g).setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER,1.0f)); // turn on opacity
g.setColor(Color.RED);
g.fillRect(20, 20, 500, 300);
}
I have tried to do it this way, but it is very flickery

As Thrasgod correctly showed in his answer, the best way is to use the paintComponent, but also if the case is to have a semi transparent JPanel (or any other component, really) and have something not transparent inside. You have to also override the paintChildren method and set the alfa value to 1.
In my case I extended the JPanel like that:
public class TransparentJPanel extends JPanel {
private float panelAlfa;
private float childrenAlfa;
public TransparentJPanel(float panelAlfa, float childrenAlfa) {
this.panelAlfa = panelAlfa;
this.childrenAlfa = childrenAlfa;
}
#Override
public void paintComponent(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
g2d.setColor(getBackground());
g2d.setRenderingHint(
RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setComposite(AlphaComposite.getInstance(
AlphaComposite.SRC_OVER, panelAlfa));
super.paintComponent(g2d);
}
#Override
protected void paintChildren(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
g2d.setColor(getBackground());
g2d.setRenderingHint(
RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setComposite(AlphaComposite.getInstance(
AlphaComposite.SRC_ATOP, childrenAlfa));
super.paintChildren(g);
}
//getter and setter
}
And in my project I only need to instantiate Jpanel jp = new TransparentJPanel(0.3f, 1.0f);, if I want only the Jpanel transparent.
You could, also, mess with the JPanel shape using g2d.fillRoundRect and g2d.drawRoundRect, but it's not in the scope of this question.

Background Image in JTextPane

How do I set a background image to a JTextPane - some sort of a watermark.
I tried this option - creating a child class of JTextPane and use the paint method to draw the image.
But then the text is displayed "below" the image than above.
Is there any "standard" or "well known" way to do this?
(BTW, I tried (something silly?) making the content type "text/html", and setting the image as the background image of a <div> but it did not help.)

Here's a working example:
import javax.swing.*;
import java.awt.*;
public class ScratchSpace {
public static void main(String[] args) {
JFrame frame = new JFrame("");
final MyTextPane textPane = new MyTextPane();
frame.add(textPane);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
private static class MyTextPane extends JTextPane {
public MyTextPane() {
super();
setText("Hello World");
setOpaque(false);
// this is needed if using Nimbus L&F - see http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6687960
setBackground(new Color(0,0,0,0));
}
#Override
protected void paintComponent(Graphics g) {
// set background green - but can draw image here too
g.setColor(Color.GREEN);
g.fillRect(0, 0, getWidth(), getHeight());
// uncomment the following to draw an image
// Image img = ...;
// g.drawImage(img, 0, 0, this);
super.paintComponent(g);
}
}
}
The important things to note:
your component must not be opaque...
so setOpaque(false);
override paintComponent(Graphics g), not paint.
paint your background, with an image
or drawing BEFORE calling
super.paintComponent(g);
If you want to master this stuff, I recommend reading "Filthy Rich Clients", a book all about how to bend Swing to your will.

Try changing the paint code to this.
public void paint(Graphics g)
{
g.setXORMode(Color.white);
g.drawImage(image,0, 0, this);
super.paint(g);
}
This would make your image to be painted before the text is rendered by the actual component's paint method.

Hmm., put a background image to the JFrame/JPanel containg the JTextPane,.. and keep the JTextPane transparent to some level.