MODULE Pong;

(****************************************************************)   
(*                      *)
(* Original author:  probably Michael Walsh     *)
(*    (The copy I got came without comments)    *)
(* Debugging by:  Peter Moylan            *)
(* Last edited:   7 December 1993            *)
(* Status:                    *)
(*    - not yet clear what this program is supposed   *)
(*      to do.  It makes pretty pictures on the *)
(*      screen, but purpose is unclear.      *)
(*    - apparently not responding to keyboard.  *)
(*                      *)
(****************************************************************)   

FROM Storage IMPORT
   ALLOCATE,DEALLOCATE;

FROM SoundEffects IMPORT
    (* proc *) Beep;

FROM Graphics IMPORT
    (* type *) ColourType,
    (* proc *) Fill,SetMode,PlotMark,PlotLine,GetScreenShape;

FROM Keyboard IMPORT
    (* proc *) InKey, KeyPressed;

CONST
   Up = 'k';
   Down = 'm';
   NewBall = ' ';
   Quit = 'q';
   None = 'a';
   PaddleSpeed = 1;
   SpeedOfBall = 1;
   
TYPE


   BallPtr=POINTER TO Ball;

   Ball=RECORD
      Xcoord:CARDINAL;
      Ycoord:CARDINAL;
      Xdir:INTEGER;
      Ydir:INTEGER;
      Colour:ColourType;
      NextBall:BallPtr;
   END; (*Ball Record*)
VAR
   Balls,LastBall:BallPtr;
   KeyIn:CHAR;
   Xmax,Ymax,PaddlePos,PaddleMoveCount:CARDINAL;
   LastColour,LastCol,ColourMax:ColourType;
   DirLast:INTEGER;
   EndOfGame,FirstBall:BOOLEAN;


PROCEDURE MovePaddle(Direction:CHAR; VAR Position:CARDINAL);
VAR
   Dir:INTEGER;
BEGIN
   IF Direction = Up
   THEN
      Dir := 5;
   ELSE
      Dir := -5;
   END(*IF*);
   IF NOT (((Position <= 5) AND (Direction = Down))
      OR ((Position + 55 >= Ymax) AND (Direction = Up)))
   THEN
      Fill(10,Position,10,Position + 50,0);
      IF Dir > 0 THEN
             Position := Position + ORD(Dir);
      ELSE
            Position := Position - ORD(Dir);
      END(*iF*);
      Fill(10,Position,10,Position + 50,3);
   END(*IF*);
   
END MovePaddle;

PROCEDURE EraseBall(Ball:BallPtr);
BEGIN
   Fill(Ball^.Xcoord,Ball^.Ycoord,(Ball^.Xcoord + 10),(Ball^.Ycoord + 10),0);
END EraseBall;

PROCEDURE DrawBall(Ball:BallPtr);
   
BEGIN
   Fill(Ball^.Xcoord,Ball^.Ycoord,(Ball^.Xcoord + 10),(Ball^.Ycoord + 10),(Ball^.Colour));
END DrawBall;

PROCEDURE CreateNewBall(VAR BallList,LastBallOnList:BallPtr;
      VAR First:BOOLEAN;
      VAR LastDir:INTEGER;
      VAR LastCol:ColourType);   
BEGIN
   
            IF First THEN
                                 NEW ( LastBall );
                    BallList := LastBallOnList;
               First := FALSE;
                                ELSE
               NEW ( LastBallOnList^.NextBall );
               LastBallOnList := LastBallOnList^.NextBall;
            END; (* if *)
            
            WITH LastBallOnList^ DO
               NextBall := NIL;
					Xcoord := Xmax DIV 2;
					Ycoord := Ymax DIV 2;
					Xdir := ((LastDir MOD 2) *2) -1;
					Ydir := ((LastDir DIV 2) * 2) -1;
					Colour := LastCol;
					LastCol:= (((LastCol + 3) MOD 7) + 1);
				END (*WITH*);
				DirLast :=(DirLast +1) MOD 4;
END CreateNewBall;

PROCEDURE MoveBalls(StartOfList:BallPtr;PaddlePosition,BallSpeed:CARDINAL);
	VAR
		CurrentBall:BallPtr;
				

	BEGIN
	CurrentBall := StartOfList;

	WHILE	CurrentBall <> NIL
	DO
		
		WITH CurrentBall^ DO
			IF (Xcoord >= 2*Xmax - 10 - BallSpeed) OR (Xcoord  <= BallSpeed)
			THEN
				Xdir := -(Xdir);
				Colour := ((Colour +1) MOD 7) + 1;
			END (*IF*);

			IF 	(Ycoord >= (Ymax -10 - BallSpeed)) OR (Ycoord <= BallSpeed)
			THEN 	
				Ydir := -(Ydir);
				Colour := ((Colour + 1) MOD 7) + 1;
			END(*IF*);
		
			IF ((Ycoord+10 > PaddlePosition)
				AND (Ycoord < PaddlePosition + 50)
				AND (Xcoord <= 10 + BallSpeed)
				AND (Xdir = -1))
			THEN
				Xdir := -(Xdir);
			END(*IF*);
		END(*WITH*);
		
		EraseBall(CurrentBall);

		WITH CurrentBall^ DO
		IF Xdir > 0 THEN
		   Xcoord := Xcoord + BallSpeed;
		ELSE
		   Xcoord := Xcoord  - BallSpeed;
		END(*IF*);
		IF Ydir > 0 THEN
		   Ycoord := Ycoord + BallSpeed;
		ELSE
		   Ycoord := Ycoord - BallSpeed;
		END(*IF*);
		END(*WITH*);
		
		DrawBall(CurrentBall);
		CurrentBall := CurrentBall^.NextBall;
	END (*DO*);	
 			
	END MoveBalls;

(****************************************************************)	

PROCEDURE RunTheGame;

    BEGIN
	PlotLine(0,0,0,Ymax,3);
	PlotLine(0,Ymax,Xmax,Ymax,3);
	PlotLine(Xmax,Ymax,Xmax,0,3);
	PlotLine(Xmax,0,0,0,3);
	FirstBall := TRUE;
	Balls := NIL;
	DirLast := 0;
	LastColour := 5;
	PaddlePos := 1;
	KeyIn := None;
	REPEAT	
	    (*PaddleMoveCount := 0;
	    REPEAT
		CASE KeyIn OF
		    Up 	: MovePaddle(Up,PaddlePos);|
		    Down	: MovePaddle(Down,PaddlePos);|
		    Quit  	: EndOfGame := TRUE;|
		    NewBall : CreateNewBall(Balls,LastBall,FirstBall,DirLast,LastColour);|
		    None : |
		ELSE
		    CreateNewBall(Balls,LastBall,FirstBall,DirLast,LastColour);
		END(*CASE*);
		IF KeyPressed() THEN
		    Beep;  KeyIn := InKey();
		ELSE
		    KeyIn := None;
		END(*IF*);
		PaddleMoveCount := PaddleMoveCount + 1;
	    UNTIL (EndOfGame) OR (PaddleMoveCount = PaddleSpeed);*)
	    CreateNewBall(Balls,LastBall,FirstBall,DirLast,LastColour);
	    MoveBalls(Balls,PaddlePos,SpeedOfBall);
		
	UNTIL EndOfGame;
    END RunTheGame;

(****************************************************************)	

BEGIN
    SetMode(16, TRUE);
    GetScreenShape(Xmax,Ymax,ColourMax);
    RunTheGame;
END Pong.