You'll need to store the line information somehow, and draw it all each frame, as without the background(...); call the particles will leave trails.

Thanks for the thinkering, removing the background leaves a bit too much of trails indeed

I was thinking saving X,Y in an array would help. The slowing down shouldn't be too much of a problem as the drawing shouldn't be much more then some lines which will get cleared at some point.

I'll have a look at arrays then

Can't seem to work out the array thing, been looking at the examples and I guess I have to work with a 2D array to store mouseX and mouseY values but that's rly as far as I get.

Help sincerely appreciated.

Thanks lenny, it helped alot. I'm able to save the mouseXY in the array and using these values to draw lines (basic drawing app). Still having some minor problems/questions though.

I'm only saving my mouseXY values when the mouse is pressed and calling those values to draw the lines. The problem is, when I release the mousepress and want to start a new line it automatically connects the point of release and the new click point with a line as the line-drawing code just takes the previous array index spot (i-1), being the point of release, and connects it with the new click point (i).
Same problem happens at the very beginning, as I start drawing it automatically takes the first value being 0,0 and connects it with the first click point x,y.

As a last thing, right now I've set my array to 1000 (to get a reasonable drawing time), what would be better is to get an array without a max size, which would be cleared every time a drawing get's cleared.

Thanks.

Code:

import processing.opengl.*; 
import processing.video.*; 

Capture camera;
int cameraWidth = 1024;
int cameraHeight = (cameraWidth/4)*3;

float x,y; 
float[] xpos=new float[1000]; 
float[] ypos=new float[1000]; 
void setup(){ 
  size(cameraWidth*2,cameraHeight); 
  smooth();
  for(int i=0;i<1000;i++){ 
    xpos[i]=x; 
    ypos[i]=y; 
  } 
  background(0,0,255); 
  stroke(255);
  strokeWeight(10);
  strokeJoin(ROUND);
  strokeCap(ROUND);

  camera = new Capture(this,cameraWidth,cameraHeight,30);
} 

void captureEvent(Capture camera)
{
  camera.read();
}

void draw(){ 
  background(0,0,255); 
  image(camera,0,0);
  //motion
  if (mousePressed == true){
    x=mouseX;
    y=mouseY;
  }

  for(int i=1;i<1000;i++){ 
    xpos[i-1]=xpos[i]; 
    ypos[i-1]=ypos[i]; 
  } 
  xpos[999]=x; 
  ypos[999]=y; 

  noFill();
  beginShape();
  for(int i=999;i>0;i--){ 
    vertex(xpos[i],ypos[i]);   
    vertex(xpos[i-1],ypos[i-1]);
  } 
  endShape();

  noFill();
  beginShape();
  for(int i=999;i>0;i--){ 
    vertex(xpos[i]+cameraWidth,ypos[i]);   
    vertex(xpos[i-1]+cameraWidth,ypos[i-1]);
  } 
  endShape();
}