GFA Mandelbrot

REM -----------------------------------------------
REM   Mandel and buddhabrot program
REM   Written by: Johan Roos Tibbelin
REM               (sjfroos)
REM   Date: 2020-08-13     Last changed:2020-08-16
REM -----------------------------------------------
REM
REM
REM mandelbrot render precalc.
INLINE brot%,32000
REM Number of iterations per pixel is saved here
DIM pixels%(320,200)
REM pixel part of set or not
DIM brot!(320,200)
SETCOLOR 0,0,0,0
SETCOLOR 15,7,7,7
REM mandelmenu(x1,y1,x2,y2)
REM foo=INP(2)
REM END
mandelbrot(-2.5,-1.2,2.5,1.2)
REM BMOVE XBIOS(2),brot%,32000
REPEAT
UNTIL MOUSEK=2
SETCOLOR 0,7,7,7
SETCOLOR 15,0,0,0
END
PROCEDURE mandelbrot(x1,y1,x2,y2)
  FOR py=0 TO 199
    FOR px=0 TO 319
      IF x1=0  AND x2=0 AND y1=0 AND y2=0 THEN
        x0=3.5/320*px-2.5
        y0=2.4/200*py-1.2
      ELSE
        x0=(x2-x1)/320*px+x1
        y0=(y2-y1)/200*py+y1
      ENDIF
      x=0
      y=0
      iteration=0
      max_iteration=40
      WHILE (x*x+y*y<=2*2 AND iteration<max_iteration)
        xtemp=x*x-y*y+x0
        y=2*x*y+y0
        x=xtemp
        iteration=iteration+1
      WEND
      IF iteration=max_iteration THEN
        color=0
        brot!(px,py)=TRUE
      ELSE
        color=iteration MOD 15
        color=color+1
        brot!(px,py)=FALSE
      ENDIF
      COLOR color
      PLOT px,py
      pixels%(px,py)=iteration
      IF MOUSEK=2 THEN
        END
      ENDIF
    NEXT px
  NEXT py
RETURN
PROCEDURE mandelmenu(VAR x1,y1,x2,y2)
  BMOVE brot%,XBIOS(2),32000
  SETCOLOR 0,0,0,0
  SETCOLOR 15,7,7,7
  foo=EVNT_BUTTON(1,1,1,mx%,my%,bu%,kb%)
  foo=GRAF_RUBBERBOX(mx%,my%,1,1,w%,h%)
  PRINT "x:";mx%;" y:";my%;" w:";w%;" h:";h%
  x1=3.5/320*mx%-2.5
  y1=2.4/200*my%-1.2
  x2=3.5/320*(mx%+w%)-2.5
  y2=2.4/200*(my%+h%)-1.2
  PRINT "p1:";x1;",";y1;" p2:";x2;",";y2
RETURN
PROCEDURE brotpack
  DIM bsum%(8)
  FOR y%=0 TO 199
    FOR x%=0 TO 319 STEP 8
      FOR bit%=0 TO 7
        b%=brot!(x%+bit%,y%)*bsum%(bit%)
      NEXT bit%
    NEXT x%
  NEXT y%
RETURN