dirtyScreen.setBounds(x1,x2,0,0);
int maxc = Math.max(getCol(pos), getCol(dirtyScreen.y));  int x1 = getPos(minr, minc);  int x2 = getPos(maxr, maxc);  dirtyScreen.setBounds(x1, x2, 0, 0);
	protected void setDirty(int pos) {	   int minr = Math.min(getRow(pos),getRow(dirtyScreen.x));	   int minc = Math.min(getCol(pos),getCol(dirtyScreen.x));	   int maxr = Math.max(getRow(pos),getRow(dirtyScreen.y));	   int maxc = Math.max(getCol(pos),getCol(dirtyScreen.y));	   int x1 = getPos(minr,minc);      int x2 = getPos(maxr,maxc);      dirtyScreen.setBounds(x1,x2,0,0);	}