IMPLEMENTATION MODULE SDLUtils ;

FROM SYSTEM IMPORT ADDRESS, ADR;
FROM SDL2 IMPORT SDL_GetError;
FROM SDLEvents IMPORT SDL_PollEvent,
   EventQuit, EventKeyDown, EventKeyUp, EventBufferBytes;
FROM libc IMPORT strlen, strncpy;

PROCEDURE CStrToM2 (src: ADDRESS; VAR dst: ARRAY OF CHAR);
VAR n: CARDINAL;
BEGIN
   IF HIGH(dst) < 0 THEN RETURN END;
   IF src = NIL THEN dst[0] := 0C; RETURN END;
   (* strlen returns CSIZE_T; VAL converts without range check. *)
   n := VAL(CARDINAL, strlen(src));
   IF n > HIGH(dst) THEN n := HIGH(dst) END;
   strncpy(ADR(dst), src, n);
   IF n <= HIGH(dst) THEN dst[n] := 0C END
END CStrToM2;

PROCEDURE GetErrorString (VAR buf: ARRAY OF CHAR);
BEGIN
   CStrToM2(SDL_GetError(), buf)
END GetErrorString;

(* Little-endian 32-bit word at byte offset off. Hosts only. *)
PROCEDURE LE32 (VAR buf: ARRAY OF CHAR; off: CARDINAL) : CARDINAL;
BEGIN
   RETURN VAL(CARDINAL, ORD(buf[off]))
        + VAL(CARDINAL, ORD(buf[off+1])) * 256
        + VAL(CARDINAL, ORD(buf[off+2])) * 65536
        + VAL(CARDINAL, ORD(buf[off+3])) * 16777216
END LE32;

PROCEDURE PollM2Event (VAR ev: M2Event) : BOOLEAN;
VAR
   buf: ARRAY [0..EventBufferBytes-1] OF CHAR;
   t: CARDINAL;
BEGIN
   IF SDL_PollEvent(ADR(buf)) = 0 THEN RETURN FALSE END;
   t := LE32(buf, 0);
   ev.sym := 0;
   ev.pressed := FALSE;
   IF t = EventKeyDown THEN
      ev.kind := evKey;
      ev.pressed := TRUE;
      (* Sint32 keysym.sym; game keycodes are all positive. *)
      ev.sym := VAL(INTEGER, LE32(buf, 20))
   ELSIF t = EventKeyUp THEN
      ev.kind := evKey;
      ev.pressed := FALSE;
      ev.sym := VAL(INTEGER, LE32(buf, 20))
   ELSIF t = EventQuit THEN
      ev.kind := evQuit
   ELSE
      ev.kind := evOther
   END;
   RETURN TRUE
END PollM2Event;

PROCEDURE DrainEvents (VAR quit: BOOLEAN);
VAR ev: M2Event;
BEGIN
   WHILE PollM2Event(ev) DO
      IF ev.kind = evQuit THEN quit := TRUE END
   END
END DrainEvents;

END SDLUtils.