Ive been making a Digital Etch a Sketch and wanted a pulsating colour background which goes though the spectrum. I have achieved the background effect but now the lines from the etch a sketch dont stay on the page. Any idea on a fix?

1. //importing
   import processing.serial.*;
   import cc.arduino.*;
   
   Arduino arduino;
   
   
   int coordX;   
   int coordY;
   int smoothcoordX;   
   int smoothcoordY;
   int prevX;  
   int prevY;
   int xPin= 0;
   int yPin= 1;
   int firstrun;
   float h = 1;
   
   
   
   void setup() {
       
   
     //println(h);
     arduino = new Arduino(this, Arduino.list()[3], 57600);
     colorMode(HSB); 
   
     size(1280,720);
     
   
    
     smoothcoordX= arduino.analogRead(xPin);
     smoothcoordY= arduino.analogRead(yPin);
   
   }
   
   void draw(){
   
   if (h >= 255)
   {
     h = 1;
   };
   h = h + 0.05;
     background(h,255,255); 
   
   
     prevX=smoothcoordX;
     prevY=smoothcoordY;
     coordX= arduino.analogRead(xPin);
     coordY= arduino.analogRead(yPin);
     smoothcoordX = prevX + coordX;
     smoothcoordY = prevY + coordY;
     smoothcoordX = smoothcoordX / 2;
     smoothcoordY = smoothcoordY / 2;
     drawLine();
   
    }
    
   
   void drawLine() {
   
     strokeWeight(3);
     stroke(20,0,30);
   
     line(map(prevX, 0, 1023, 10, 1270),
          map(prevY, 0, 1023, 10 , 710),
          map(smoothcoordX,  0, 1023, 10, 1270),
          map(smoothcoordY,  0, 1023, 10, 710));
   
   }