Million ways to do this. Here is an example which shows the basics of the technique you describe...

1. PGraphics normalImage;
2. PImage glowImage;
3. 
   
4. void setup() {
5.   size(500,500);
6.   normalImage = createGraphics(width,height,JAVA2D);
7.   normalImage.beginDraw();
8.   normalImage.smooth();
9.   normalImage.stroke(255); 
10.   normalImage.strokeWeight(2); 
11.   normalImage.endDraw();
12. }
13. 
    
14. void draw() {
15.   background(0);
16.   glowImage = normalImage.get(0,0,normalImage.width,normalImage.height);
17.   glowImage.resize(0,width/4);
18.   glowImage.filter(BLUR,2);
19.   glowImage.resize(0,width);
20.   image(glowImage,0,0);
21.   image(normalImage,0,0);
22. }
23. 
    
24. void mouseDragged() {
25.   normalImage.beginDraw();
26.   normalImage.line(mouseX,mouseY,pmouseX,pmouseY);
27.   normalImage.endDraw();
28. }

ok thanks, perfect it does exactly what i want. but..

ok, it's quite done.

i've tried to download neon effect zip from googlcode and vitaminic lib.

i've tried to download neon effect zip from googlcode and vitaminic lib.