I use noloop() in my setup(). But I called  draw() methode after I make changes.

Does that mean you call draw from the JSlider value change handler? If not then that would explain why nothing is being drawn.

Strangly when I change the size of the JPanel, it redraw itself.

Not so strange since resizing the JPanel will result in the panel and all sub-components (including the PApplet) to redraw themselves. This suggests that if you call repaint on the panel e.g.

1. panelName.repaint();

then it will probably cause the PApplet to redraw itself, so you might try that.

thanks, quarks,

Most books concentrate on the Java language syntax rather than how it works under the hood but this article might help.

The PApplet is a sub class of the Java AWT class Applet so much the article is relevant but AFAIK PApplet disables the repaint() method so that you cannot use this to update the graphics. Since you have used noLoop() then you have to use Processing's redraw() method (which you did).

HTH

quarks, thanks for the link, a very good explanation to what happened under hood in java.

One further question is what is the relationship between redraw() and repaint()? Will redraw() call repaint internally so that paint() is called which will call draw(), or something else?

In Java AWT you place the drawing code inside the paint method and then call the repaint method. The repaint method does not actual call the paint method directly but posts a PaintEvent object on the event queue. The main thread is responsible for processing the event queue and when it removes the PaintEvent object it calls the paint method for us.

Now in Processing the PApplet (sketch) class inherits from the Java AWT Applet so there is still a paint and repaint method. The repaint method is unchanged so it still posts PaintEvent but Processing's PApplet overrides the default paint method. SO repaint still posts a PaintEvent but when it is processed it executes the paint method in PApplet.

Now the paint method gets a little complicated because of the different renderers (JAVA2D, P2D, P3D & OPENGL) but effectively the logic is the same. PApplet has two boolean variables looping and redraw. These are controlled with the methods

loop()    sets looping = true
noLoop()  sets looping = false
redraw()  sets redraw = true

Now the paint method does a lot of things but it will ONLY execute the draw() method if EITHER looping OR redraw is true. At some point the redraw variable is set back to false so that the draw method is only executed once, provided looping is false of course.

Here is the source code (minus comments) for the redraw method from the PApplet class.

1.   synchronized public void redraw() {
2.     if (!looping) {
3.       redraw = true;
4.     }
5.   }

HTH

Thanks quarks,
So redraw() only change the flag. 
If I want a repaint(), I must call repaint() AND redraw()?
I ask this only because I called redraw(), sometimes It works but if I call redraw() too fast It seems that the Applet refused to  redraw() itself after that, whatever I do.

If I want a repaint(), I must call repaint() AND redraw()?

Yes but you need to call redraw() first so the flag is set. The call to repaint will then post the PaintEvent which will then be picked up when the event queue is processed thus making sure the draw() method gets executed.

Hi quarks,

thanks again for your replay, It did that, it does not work.
Before call redraw() the applet must do some calculation to update the state of the data used to draw. It seems that before that calculation finished draw() will not be called. And if before it finished I again called the calculation function the call to redraw() is kind of omitted...forever!

And it seems that call redraw() alone will normally cause draw() be called.

And it seems that call redraw() alone will normally cause draw() be called.

I am positive my description of Java AWT painting is correct but I think I made a mistake when I described Proccesings inner workings .

AFAIK the PApplet paint method is called frequently and that method calls the sketch's draw() method but ONLY if looping or redraw is true. This would mean that you only have to call the redraw() method to update the display.

Before call redraw() the applet must do some calculation to update the state of the data used to draw.

I understand that.

It seems that before that calculation finished draw() will not be called.

Makes sense only to display the data after its been calculated - so I understand that.

And if before it finished I again called the calculation function the call to redraw() is kind of omitted...forever!

Not sure if I understand this.


Are you saying that the update algorithm is this

• Caluclate latest state of data
• Call redraw()

Is it possible to exit the 'calculate' code before it is finished?
Is the calculation part executed in a separate thread?

If either is true then you have to modify the program to ensure that the GUI has a chance to update the display before a new set of calculations are performed. There are a number of techniques to do this but would need more info about the type of data, the type of calculations and how the update is triggered.

thanks, quarks,
my function does something like this. When this function is called too frequent from the ChangeListener() of the Jslider, the draw() method is not called and if change the size of the parent frame so that a system call to repaint is tragerd, the graph broken show gray panel.

This is strange in that if I do it slowly it works.
 
 public void setSource(DataSource dataSource) {

        this.data = dataSource;

        this. do some calculation

        // repaint the layers
        this.redraw();
        this.repaint();

        // give report
    }

When you drag on a JSlider it creates ChangeEvent objects and puts them on the event queue. This queue also has the PaintEvent objects as well. Only one event can be processed at a time, I suspect that the PaintEvents are not being interpersed with the ChangeEvents but I am not sure why.

One possibility is that the calculations are taking a significant amount of time so the application becomes sluggish processing events.

if change the size of the parent frame ...

there is no easy solution for this because PApplet extends Applet and since applets were designed to be shown in web pages they can not be resized - I suggest that you prevent the JFrame from being resized - using setResizable(false) but only after you have made the frame visible.