A mouse listener calls repaint() and I can see that it does actually go past the drawing part because I see globalcounter incremented in the output of System.out.println(). On the screen, however, I don't see any change until I minimize the window and maximize again, resize it, or move it out of the visible screen area and back in. Obviously I'd like it to update without my intervention.
class GUI extends javax.swing.JFrame {
int globalcounter=0;
class MyCanvas extends Canvas {
#Override
public void paint(Graphics g) {
globalcounter++;
g.drawString(globalcounter,100,100);
System.out.println(globalcounter);
}
}
}
(Originally I was loading an image from a file that got constantly updated (webcam) and painting it on the canvas. When I dragged it partly out of the visible screen area and back in, the part that has been 'outside' was refreshed, the rest not.)
revalidate() instead of repaint() didn't change anything.
I know this post is a duplicate to Java repaint not working correctly but when I posted it there it was deleted.
Why are you adding an AWT component, Canvas, to a Swing component, JFrame? You should stick with Swing components only. And also do you know the size of your MyCanvas, and how have you added it to the JFrame as you don't show this code.
Consider
using a JPanel instead of a Canvas object,
drawing in its paintComponent method,
showing us an sscce if you're still stuck.
And also, if all you're doing is drawing text, use a JLabel rather than drawing in paint/paintComponent, and change its text with its setText(...) method.
Related
JPanel.setBackground method does nothing (although opaque attribute is true) if super.paintComponent father method isn't being called.
I have read a lot of similar questions here about this issue, and in each one of them I've only found solutions without explanation that helped me to understand why setBackground method when written before adding the JPanel to JFrame changes the JPanel background color, while when the setBackground is written inside paintComponent nothing is changed (only when calling father's paintComponent method as already mentioned).
Is it somehow related to Graphics object?
I have tried to change JPanel's opaque attribute to true and using setBackground(COLOR.BLACK) in paintComponent() method I had overriden in a class that extends JPanel
paintComponent(Graphics g)
{
this.setOpaque(true);
this.setBackground(COLOR.BLACK);
}
I expect that the JPanel background color will be black
Instead, background color is the default one
Well, first of all if you're using paintComponent(Graphics g) method, the first line you need to have inside is: super.paintComponent(g) otherwise you're breaking the paint-chain.
This will allow the parent component to draw the default component, before any customizations you do to it. If you don't do it, well, is like having a drawing in a piece of paper, imagine a circle, then cutting that circle and then trying to paint the outside.
Here's a more in-depth answer to How does super.paintComponent(g) works
However I wouldn't write
this.setOpaque(true);
this.setBackground(COLOR.BLACK);
inside the paintComponent(...) method, as it gets called several times and you can't control when it will ever get called. I would put those lines in a constructor, unless you want to change it later in your program while it's being painted depending on the state of your program or a gradient maybe.
For this part:
why setBackground method when written before adding the JPanel to JFrame changes the JPanel background color
Honestly, I don't understand what you mean.
Why do you say that if i won't call super.paintComponent(),it will break the chain? It's still drawing all the shapes and lines i want using graphics object.
From the docs:
The JPanel has a UI delegate which performs the background painting for itself. You call it by using super.paintComponent(g) and we pass the Graphics component to prevent irrevocable changes such as Graphics.translate
Your JPanel knows how to paint its children, but requires some help to paint itself, and this help comes from its parent.
When I mentioned "break the paint chain" I didn't mean nothing would paint, but that you would get strange behaviors such as the one of the JPanel's background disappearing or not being set.
In addition,something weird happens if the argument i'm sending to setBackground method is a random color(using Random object). JPanel changing color very quickly although i'm not doing anything(not minimizing,not resizing,etc).Can you consider why?
As I said before, the paintComponent gets called several times and you don't have control over when it will be called, even moving your mouse or something else will trigger the panel to repaint.
I am doing a project with double buffering. When I paint, it simply paints on top of the old layers, but I need to erase them. Repaint() didn't work, but I'm guessing something equally as simple is the answer.
Any ideas?
Added code, and now it disappears, but it erases the background color.
public void paint(Graphics g)
{
super.paint(buffer);
for(Projectile p: projectiles)
drawRectImage(buffer, p.image, p.getRectangle());
}
Suggestions:
If this is a Swing GUI, then don't override the paint method, but instead override the paintComponent method. This won't help your current problem, but will help prevent future problems including problems with painting of borders and child components.
If Swing (again you don't say), then make sure that your painting component extends JPanel, not JComponent, since JPanel is opaque and fills its background rectangle in its super method.
If it's not Swing, then you should strongly consider changing from AWT to Swing.
If you're still stuck, then yep, you'll want to create and post a minimal example program. Please check out the link.
So this question has two parts, which I think may be related, and it's mostly abstract. Briefly, here's what I'm doing:
I have a JFrame with a JPanel and some child JPanels each with 3 JButtons on it. I also created a JComponent called glassPanel for the JFrame (i.e. myJFrame.setGlassPane(glassPanel)), that allows me to paint over the JPanels and buttons.
(1) Essentially triggered by clicking all 3 buttons on a JPanel, glassPanel is set to Visible (which appears to then call paintComponent()). This is relates to the first question.
(2) In paintComponent() I draw and paint rectangles and images, using a double buffer, onto glassPanel. This is relates to the second question.
Here's my relevant GlassPanel class code (this is not an SSCCE because it is an abstract question for now):
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Line2D;
import javax.swing.JComponent;
public class GlassPanel extends JComponent {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
setDoubleBuffered(true);
Graphics2D g2 = (Graphics2D) g;
g2.drawRect(x,y,width,height);
g2.fillRect(x,y,width,height);
g2.drawImage(img, x, y, this);
}
}
By placing a System.out.print statement inside the paintComponent() method, I could tell it was being called continuously and also asynchronously. For how I think the call is made, see (1). Also, let's say I'm absolutely certain there is no call to repaint() anywhere in the code (I've checked many, many times). This is the basis of the first question.
The first time I click 3 buttons, all goes smoothly. The rectangle and images are both drawn immediately. However, when I click the next 3 buttons (at this point, glassPanel has already been setVisible(true) and the first rectangle and image are still on the screen, painted over the first 3 buttons), the second rectangle and image only load partially. When I click away from the JFrame and onto the Eclipse window that I've run the program from, the number of calls to paintComponent() rapidly increases by the same amount each time AND the partially loaded image(s) and rectangle(s) immediately and completely show up in the background JFrame. When I click back to the JFrame, the number of calls goes up again by an exact amount). This is the basis of the second question.
UPDATE: Here's something I read:
Also, when the GUI is covered by another window and then becomes
uncovered, the painting system invokes the paintComponent method with
the painting area equal to the newly uncovered area.
My questions are:
(1) why might paintComponent() be called so much without a repaint()? Or, a similar question, what might be calling paintComponent()?
UPDATE: After doing a little math, I strongly believe that it's being called by every component (all buttons and panels) continuously. But still, no call to repaint()...
(2) Why are the images loaded partially until i take focus from the JFrame window?
Note that I have tried many things: (a) creating my own doubleBuffer and using no double buffer (I know it's mostly for animation), (b) overriding and not overriding paintComponent(), (c) drawing and not drawing the image (the rectangle still takes time to load), (d) making absolutely sure there was no repaint(), (e) using and not using SwingUtilities.invokeLater(new Runnable() {
public void run() { //stuff});, (f) done an if statement to only setVisible(true) once.
I can try and past the SSCCE if I must, but I do think these are more abstract. Thanks!
Well, I think I've answered both questions. For the first, why paintComponent() was being called continuously, was that it was not actually being called continuously. It was being called by all the components when it first shows the GUI. When the Eclipse window covers it and then uncovers it, it gets called more times.
For the second, it has to do with the clipBounds of the Graphics2D object/thing. I found out how the clipBounds were changing for each paint call, so when I set the clip at the start of the paintComponent() method, the images show up immediately. (BTW, It looks GREAT!).
With a twist: after an image is displayed, each click of a button does something to the image. I haven't figured out what exactly, though. It almost looks like its repainting the same image over the old images.
So I have to figure out how to keep the old images but draw new ones when appropriate and only draw/add the new ones onto the glassPanel.
UPDATE: Calling repaint() immediately after each button is clicked helps a little. But it still causes the image to flicker somewhat, as if adding another layer, as the button is pressed, and then it returns to normal when the user lets go.
In my code I override the paintComponent method and draw a rectangle inside JPanel.
The JPanel is then added to JFrame and I use a method that updates the position of the rectangle via a Thread.
The rectangle does actually move .. but only when I minimize the window and maximize it back again. So in other words.. it doesn't do it as I'm looking at it.. the rectangle will just sit there.. but after I minimize and bring the window back up, the rectangle will have moved.
What can I do to fix this?
I am guessing you forgot to call the Repaint of the JPanel whose paintComponent you are overriding everytime you update the object. The reason you are only seeing the change on minimize/maximize is because that is when swing calls the repaint of the component.
I am creating a program in which the user can draw lines and erase them. I am able to create my window and create a functioning JMenuBar. When the drawing capability is not enabled, everything is fine. But when the drawing capability is enabled, a second JMenuBar is painted below the original. This menu bar is not functional, and sometimes when it is drawn, ALL of the graphics on the screen are repainted lower as well. Re-sizing the window in any way remedies these problem.
I would post pictures but, you know, I'm a new user and can't.
I have been able to narrow the problem down to a point in my paint() method. Need to know: When the mouse is dragged, the repaint() method is called. It uses my paint() method which calls the paintObject(Graphics g) method in my Line class. The JMenuBar error is appearing at the END of the paint method in the top class.
public void paint(Graphics g)//paint() in the top class
{
for(int i = 0; i < objs.size(); i++)//Loop that finds all Tool(Line) objects that
((Tools)objs.get(i)).paintObject(g);//have been drawn, and redraws them.
//This part of the code completes successfully with no error.
}//ERROR OCCURS HERE!!!!!!
I have no idea why this is happening. As a side note, there is also a JTextField on the screen that doesn't appear until it is highlighted. Thanks for at least reading this far!
Edit: I'll go on a limb, I'll bet you in fact are drawing directly on the top level window (JFrame or JApplet or JDialog...) and have added the mouse listener to this window as well -- hence the drawing of components translated down a bit.
The solution is to look at the tutorials first before attempting something fairly complex like this. They'll tell you how to draw correctly including the suggestions I've given in my comments, such as drawing in a JComponent or JPanel's paintComponent method and calling the super.paintComponent(g) method as the first method call of your paintComponent override.