DECLARE SUB setpal ()
DECLARE SUB showpic1 ()
DECLARE SUB filter ()
DEFINT I-N
                                   'low-pass filter
                                   'used to blur vertically
                                   'then horizontally
SCREEN 12
VIEW (160, 80)-(480, 400), , 12
WINDOW (0, 0)-(64, 64)
CONST grey0 = 65536 + 256 + 1

DIM SHARED pic1(63, 63) AS INTEGER, pic2(63, 63) AS INTEGER
CONST k1 = 1024
CONST c1 = k1 / 16

DIM SHARED filt(-1 TO 1, -1 TO 1)
FOR i = -1 TO 1
   FOR j = -1 TO 1
      READ filt(i, j)
   NEXT
NEXT

DATA    1, -2,  1
DATA   -2,  4, -2
DATA    1, -2,  1

setpal
RANDOMIZE TIMER

FOR i = 0 TO 63              'Diamond on shaded background
   FOR j = 0 TO 63
      k = j - ((ABS(i - 32) + ABS(j - 32)) < 16) * 16
      pic1(i, j) = k
   NEXT
NEXT

showpic1


filter

SUB filter
FOR i = 1 TO 62
   FOR j = 1 TO 62
      m = 0
      FOR k = -1 TO 1
         FOR l = -1 TO 1
            m = m + pic1(i + k, j + l) * filt(k, l)
         NEXT
      NEXT
      pic2(i, j) = m / 8 + 8
      LINE (i, j)-STEP(1, 1), pic2(i, j), BF
   NEXT
NEXT

END SUB

SUB setpal
FOR i = 1 TO 15
   PALETTE i, 4 * i * grey0
NEXT
END SUB

SUB showpic1
FOR i = 0 TO 63
   FOR j = 0 TO 63
      LINE (i, j)-STEP(1, 1), pic1(i, j) \ 4, BF
   NEXT
NEXT
END SUB