\ animation - boxes bouncing off picture
const numboxes=10;

var xbox{numboxes},ybox{numboxes},
    xincr{numboxes},yincr{numboxes},
    i,picnum;

procedure movebox(i); \ Move box i, bouncing off wall if needed
  begin
    xbox{i}:=xbox{i}+xincr{i};
    if xbox{i}<10 then
      if xincr{i}<0 then
        xincr{i}:= -xincr{i};
    if xbox{i}>490 then
      if xincr{i}>0 then
        xincr{i}:= -xincr{i};
    ybox{i}:=ybox{i}+yincr{i};
    if ybox{i}<10 then
      if yincr{i}<0 then
        yincr{i}:= -yincr{i};
    if ybox{i}>290 then
      if yincr{i}>0 then
        yincr{i}:= -yincr{i};
  end;

begin
  call cvclear;
  picnum:=1;
  call wait(2000); \ wait 2 secs for user
  i:=0;
  while i<numboxes do
    begin
      while cvx<0 do \ want canvas position
        call wait(10);
      xbox{i}:=cvx;
      ybox{i}:=cvy;
      call cvbox(xbox{i}-10,ybox{i}-10,20,20);
      xincr{i}:=5;
      yincr{i}:=5;
      call wait(1000);
      i:=i+1
    end;
  while 1=1 do
    begin
      while cvx<0 do \ Continue while cursor off canvas
        begin
          call cvclear;
          i:=0;
          while i<numboxes do
            begin \ Move all the boxes, bouncing if needed
              call cvbox(xbox{i}-10,ybox{i}-10,20,20);
              call movebox(i);
              i:=i+1
            end;
          call wait(10)
        end;
      while cvx> -1 do \ Continue while cursor over canvas
        begin
          call cvclear;
          call cvdraw(picnum,cvx-40,cvy-50,80,100);
          i:=0;
          while i<numboxes do 
            begin \ Move all the boxes, bouncing if needed
              call cvbox(xbox{i}-10,ybox{i}-10,20,20);
              call movebox(i);
              \ Detect collision with picture and bounce
              if xbox{i}>cvx-45 then
                if xbox{i}<cvx+45 then
                  if ybox{i}>cvy-55 then
                    if ybox{i}<cvy+55 then
                      begin
                        xincr{i}:= -xincr{i};
                        yincr{i}:= -yincr{i}
                      end;
              i:=i+1
            end;
          call wait(10)
        end;
      call cvclear;
      picnum:=picnum+1; \ change picture
      if picnum=4 then
        picnum:=1
    end
end.