OPTION ANGLE DEGREES
INPUT PROMPT "何度の方向から観察しますか？ ( 0 〜 90 )  ":U
SET WINDOW -55,55,-55,55
FOR i=0 TO 360*5 STEP 2
   SET DRAW mode hidden       ! ちらつき防止
   CLEAR
   FOR j=O TO 360 STEP 10
      LET Q=SIN(i+j)
      IF Q^2<SIN(U)^2 THEN
         LET Q=SIN(U)
      END IF
      IF U<2 THEN
         IF SIN(i+j)>0 THEN
            DRAW disk WITH SCALE(Q,1)*SHIFT(50*COS(i+j),0)
         END IF
      ELSE
         DRAW disk WITH SCALE(Q,1)*SHIFT(50*COS(i+j),-50*U*SIN(i+j)/90)
      END IF
   NEXT j
   WAIT DELAY 0.01
   SET DRAW mode explicit   ! ちらつき防止
NEXT i
END