MODULE update;

(* Bouncing ball demo: per-frame state updates on the tigr real-time
   window. *)

FROM tigr IMPORT TigrPtr, tigrWindow, tigrFree, tigrClosed, tigrClear,
                tigrUpdate, TPixelType, tigrFillCircle,
                TK_ESCAPE, tigrKeyDown;
FROM helper IMPORT tigrRGB;

VAR
    screen          : TigrPtr;
    posx, posy      : INTEGER;
    velx, vely      : INTEGER;
    radius          : INTEGER;
    w, h            : CARDINAL;
    black, ball     : TPixelType;

BEGIN
    screen := tigrWindow(320, 240, "update", 0);
    posx   := 160;
    posy   := 120;
    velx   := 3;
    vely   := 2;
    radius := 20;
    black  := tigrRGB(0, 0, 0);
    ball   := tigrRGB(230, 60, 60);

    WHILE (NOT (tigrClosed(screen) > 0)) AND (NOT (tigrKeyDown(screen, TK_ESCAPE) > 0)) DO
        w := screen^.w;
        h := screen^.h;

        posx := posx + velx;
        posy := posy + vely;

        IF (posx - radius) <= 0 THEN
            posx  := radius;
            velx  := -velx;
        END;
        IF (posy - radius) <= 0 THEN
            posy  := radius;
            vely  := -vely;
        END;
        IF (posx + radius) >= INTEGER(w) THEN
            posx  := INTEGER(w) - radius;
            velx  := -velx;
        END;
        IF (posy + radius) >= INTEGER(h) THEN
            posy  := INTEGER(h) - radius;
            vely  := -vely;
        END;

        tigrClear(screen, black);
        tigrFillCircle(screen, posx, posy, radius, ball);
        tigrUpdate(screen);
    END;
    tigrFree(screen);
END update.