All the text area that I found cant be append.

What have you found?

The easiest solution is to store the text (program output) in a String or String array and append the latest data to this. Everytime you append data display the new String/String array in your text area component replacing the existing text.

So far I have been using the ControlP5 library and check the G4P library too. I have tried that method by keep appending the string before. But this way, the text area won't handle the "\n", it will throw an error. So the text will keep continuing in one line. I would like it to be on the next line. Is this possible?

I don't know about ControlP5 but G4P should do what you want.

In G4P when you create the textfield add 'true' as the final parameter e.g.

GTextField txf;

and in setup

txf = new GTextField(this, "Initial text", 20, 30, 300, 200, true);

This will create a multiline textfield (300x200 pixels in size located at [20,30]) and you can get the text as a single string with embedded \n using

t = txf.viewText();

Then append some text and redisplay with

t += "\nNew text line 1 \nNew text line 2";
txf.setText(t);

where t is a String

Yes I tried using the TextField, it works, but since it is a textField, it allow the user to edit it, and it doesn't scroll when the line is more than the area. I don't see the option for this, any idea on this?

For full clarity, here's how you could do it in controlP5 0.7.3 with a Textarea.

Code Example

1. import controlP5.*;
2. ControlP5 cp5;
3.  
4. Textarea myTextarea;
5.  
6. void setup() {
7.   size(700,400);
8.   cp5 = new ControlP5(this);
9.  
10.   // create a textarea, scroll to the end and turn the scrollbar off
11.   myTextarea = cp5.addTextarea("txt").setPosition(100,100).setSize(300,100).setLineHeight(14)
12.     .setColorBackground(color(255,100)).setColorForeground(color(255,100))
13.     .scroll(1).hideScrollbar();
14. }
15.  
16. void draw() {
17.   background(0);
18.   if (frameCount % 10 == 0) {
19.     String s = myTextarea.getText();
20.     s += "Adding some text @ frame: " + frameCount + " (still working! ;-) \n";
21.     myTextarea.setText(s);
22.   }
23. }

It works! Thank you so much!