Объясните что за что отвечает в этом коде, а то ничего не понятно :( Uses graphABC,ABCObjects;
var
i,xhead,yhead,z,appleX,appleY:integer;
head:CircleABC;

snake:array[1..4] of CircleABC;
apple:circleABC;
score:TextABC;

procedure keyDown(key:integer);
begin
if(key = vk_Right) then z := 1;
if(key = vk_Left) then z := 2;
if(key = vk_Up) then z := 3;
if(key = vk_Down) then z := 4;
end;

begin

for i:=0 to 6 do
begin
line(0,i*80,windowWidth,i*80);
end;

for i:=0 to 8 do
begin
line(i*80,0,i*80,windowHeight);
end;

xhead := 3*80 - 40;
yhead := 2*80 - 40;

appleX := 6*80 - 40;
appleY := 3*80 - 40;

apple := CircleABC.Create(appleX,appleY,40,clRed);

head := CircleABC.Create(xhead,yhead,40,clBlue);

for i:=1 to 4 do
begin
snake[i] := CircleABC.Create(xhead,yhead+80*i,40,clBlue);
end;

score := TextABC.Create(5,0,80,'0',clGreen);

while(true) do
begin

onKeyDown := keyDown;

if(z <> 0) then
begin
for i:=4 downto 2 do
begin
snake[i].MoveTo(snake[i-1].Position.X,snake[i-1].Position.Y);
end;

snake[1].MoveTo(xhead-40,yhead-40);
end;

if(z = 1) then xhead := xhead + 80
else if (z = 2) then xhead := xhead - 80
else if (z = 3) then yhead := yhead - 80
else if (z = 4) then yhead := yhead + 80;

if(xhead > windowWidth) then xhead := 40;
if(xhead < 0) then xhead := windowWidth - 40;
if(yhead > windowHeight) then yhead := 40;
if(yhead < 0) then yhead := windowHeight - 40;

if((xHead = appleX) and (yHead = appleY)) then
begin

appleX := random(1,8)*80 - 40;
appleY := random(1,6)*80 - 40;
apple.MoveTo(appleX-40,appleY - 40);
score.Text := ((score.Text).ToInteger + 1).ToString();

end;

head.MoveTo(xhead-40,yhead - 40);
sleep(200);
end;

end.