public void setup()
{
     size(640,480);
}
int[] pix = new int[640*480];
int RR=0,GG=0,BB=0;
public void draw()
{  
    background(0,255,0);
    fill(255,0,0);
    noStroke();
    rect(0,height/2,width,height/2);

    fill(0,0,255);
    rect(width/2,0,width/2,height);
        
    fill(0);
    textSize(20);
    text(RR+" "+GG+" "+BB,100,100);

    loadPixels();
    if(pixels!=null)
    {
        for(int i=0;i<pix.length;i++)
           pix[i] = pixels[i];
    }    

}

public void mouseClicked()
{
   if(pix!=null && pix.length>0)
   {
     int p = pix[(int)mouseY*640+(int)mouseX];
     RR = (((p>>16)%256)& 0xFF);
     GG = (((p>>8)%256)& 0xFF);
     BB = ((p%256)& 0xFF);
   }  
}

Code 0-1: Pixeltest -- Es werden die Rot-Grün- und Blau-Anteile des angeklickten Pixels angezeigt.

// 1m == 100Pixel
int kantepix = 20; //Jedes Quadrat ist 20cm gross.
ArrayList<int[]> merker = new ArrayList<int[]>();
public void setup()
{
     frameRate(40);
     size(640,480);
     textAlign(CENTER);     
}

public void draw()
{
    background(255);
    stroke(0);
    int zaehler=0;
    for(int i=0;i<(int)height;i+=kantepix)
    {
         for(int k=0;k<(int)width;k+=kantepix)
         {
             noFill();
             rect(k,i,kantepix,kantepix);
             fill(0);
             text(""+zaehler,k+kantepix/2,i+kantepix/2);
             zaehler++;
         }
    }    
    fill(255,0,0);
    noStroke();
    for(int i=0;i<merker.size();i++)
    {
         int nummer = merker.get(i)[0];
         
         int xx = kantepix*(nummer%((int)width/kantepix));
         int yy = kantepix*(nummer/((int)width/kantepix));
         
         rect(xx,yy,kantepix,kantepix);
    }
}

public void mouseClicked()
{
     int nummer = ((int)mouseY/kantepix)*((int)width/kantepix) + (int)mouseX/kantepix;
     merker.add(new int[] {nummer});
     
}

public void keyPressed()
{
    if(key==' ')
    {
         String[] s = new String[merker.size()];
         for(int i=0;i<s.length;i++)
         {
              s[i] = ""+merker.get(i)[0];
         }
         saveStrings("hindernisse.txt",s);
    }
}

Code 0-2: Editor.