%begin
!Solid body modeller - original version by P. Reid.
!Looks a hack - no clipping and crashes out frequently.
!Modded JHB Oct 86
!All comments inserted by JHB from examination of program.

   !Input file Formats:
   !1) Peter Reid's format...
   !All text ignored up to and including a '#' character.
   !Then up to 58 point sets may follow. Each of form..

   !First printable character taken as point set name. 'A'<=char<='z'
   !then lines may be..
   !Point description:
   !   Point number (ignored), ':' then X,Y,Z
   !End of list: '$'
   !Set name of '$' terminates list of sets

   !Polygon list.
   !All text ignored up to '#', then lines may be..
   !Colour indication:
   !   '>' followed by colour no. or INVISIBLE (255) then colour no.
   !Polygon description:
   !   (ignored) ':' followed by number of vertices then vertex list.
   !   Vertices specified as SETm, SETn,.... where SET is the set name ('A'-'z')
   !End of list: '$'

   !?Viewpoint description:
   !Text ignored up to '#', then
   !number (ignored), sp_cx, sp_cy, sp_dist, xa, ya, za

   !2) Iff' (JHB)

!&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
%include "level1:graphinc.imp"

@16_E30000 %short %integer %array Colour Map (0:511)
%routine Mix Colour (%short Col, Red, Green, Blue)
   Colour Map(Col<<1+1)=Red+Green<<5+Blue<<10
%end

%routine VClear
   Print Symbol (27); Print Symbol (118)
%end

%routine Clear All
   VClear
   Clear
%end

%routine Set Up
%integer i
%integer z = 0
  Offset (0,0)
  Colour (White)
  %for i = 0, 32, 480 %cycle
     Colour Map (1+i)  = z
     Colour Map (3+i)  = 31
     Colour Map (5+i)  = 31<<5
     Colour Map (7+i)  = 31<<5+31
     Colour Map (9+i)  = 31<<10
     Colour Map (11+i) = 31<<10+31
     Colour Map (13+i) = 31<<10+31<<5
     Colour Map (15+i) = 31<<10+31<<5+31
     Colour Map (17+i) = 31<<10+31<<5+31
     Colour Map (19+i) = 31<<10+31<<5
     Colour Map (21+i) = 31<<10+31
     Colour Map (23+i) = 31<<10
     Colour Map (25+i) = 31<<5+31
     Colour Map (27+i) = 31<<5
     Colour Map (29+i) = 31
     Colour Map (31+i) = z
  %repeat
%end
!&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
%include "inc:random.imp"
%include "inc:util.imp"
%const %real PI = 3.141592653589793238462643
%external %real %fn %spec Sin (%real x)
%external %real %fn %spec Cos (%real x)
%const %byte XY = 0, XZ = 1, YZ = 2
%const %integer PMax = 3000; ! max points & polygons
%const %integer Max Stars = 100
%short %array Stars (1:Max Stars,1:2)
%short OX, OY, MX = -1, MY = -1,Temp, Di = 10
%integer StB,StT
%string (30) File,fa,fb
%const %short One  = 16_4000,
              Zero = 0,
              f128 = One>>7
%const %byte Background = 9, Shade Line Col = Black, Hidden Poly Col = Black,
             Hidden Line Col = White, Wire Col = White, Invisible = 255
%const %integer Big = 256 << 6 - One
%record %format Pt  (%short X, Y, Z)
%record %format RPt  (%real X, Y, Z)
%record %format Matrix (%record (Pt) A,B,C)
%record (Matrix) R,T
%short %array Sine, Cosine (0:359)
%record %format Polt (%short Depth, %byte Num,Col,Col2,
                      %record (Pt) %array V(1:32))
%record (Pt) %array %name PV (1:32)
%record (Pt) %name PpV, QpV
%record (Polt) %array P,Q (0:PMax)
%record (Polt) %name Pp,Qp
%record (Polt) %name %array PL (0:Pmax)
%switch TD (32:122)
%const %short Ambient = 8
%short xp,yp,Ang = 30, Max
%const %real Rad = Pi/180
%const %byte True = 1, False = 0
%byte Shading = False, Shade Line = False, Hidden = False, Show = True
%byte Moving = False, Changing = False, Show Stars = False, ReCalc
%real A,Len
%short Sc, xa, ya, za
%integer Num Ships
%record %format SF (%short CX, CY, Dist)
%record (SF) Sp
%record (RPt) Light
%integer CX,CY
%short DS
%short Lx = 10, Ly = -10, Lz = -10
%integer ships,ii,i,j,k,NumPoly
%byte MB

%short %fn Product (%short A,B)
%short Res
   *Move.w A,d0
   *Muls   B,d0
   *Asl.l   #2,d0
   *Swap   d0
   *Move.w d0,Res
   %result = Res
%end

%routine Rite (%short n)
   Print (Float(n)/One,2,4)
%end

%routine Swap (%short %name A, B)
   %short temp
   Temp = A; A = B; B = Temp
%end

%routine Transpose (%record (Matrix) %name M)
   Swap (M_A_Y, M_B_X)
   Swap (M_B_Z, M_C_Y)
   Swap (M_A_Z, M_C_X)
%end

%routine Transform (%record (Matrix) %name M, %record (Pt) %name O,O2)
%record (Pt) N
   N_X =Product(O_X,M_A_X)+Product(O_Y,M_A_Y)+Product(O_Z,M_A_Z)
   N_Y =Product(O_X,M_B_X)+Product(O_Y,M_B_Y)+Product(O_Z,M_B_Z)
   N_Z =Product(O_X,M_C_X)+Product(O_Y,M_C_Y)+Product(O_Z,M_C_Z)
   O2 = N
%end

%routine MMult (%record (Matrix) %name P,Q)
   Transpose (Q)
   Transform (P, Q_A, Q_A)
   Transform (P, Q_B, Q_B)
   Transform (P, Q_C, Q_C)
   Transpose (Q)
%end

%byte %fn Get Mouse
%byte M,N
%integer i
   %cycle
      M = Mouse Buttons
      N = Mouse Buttons %for i = 1,1,2000
   %repeat %until M = N
   %result = M
%end

%routine Convert
   OX = MX; OY = MY
   MX = (MouseX//3) & 1023
   MY = (MouseY//3) & 1023
%end

%routine Rotate (%short xa, ya, za)
   %record (Pt) %name PpV, QpV
   %record (Matrix) R,T
   %integer i,j

   T_A_X = One;  T_A_Y =   0; T_A_Z = 0
   T_B_X =   0;  T_B_Y = One; T_B_Z = 0
   T_C_X =   0;  T_C_Y =   0; T_C_Z = One

   %if za # 0 %start
      R_A_X = Cosine (za);  R_A_Y =   Sine (za);  R_A_Z = 0
      R_B_X =  -Sine (za);  R_B_Y = Cosine (za);  R_B_Z = 0
      R_C_X =           0;  R_C_Y =           0;  R_C_Z = One
      MMult (R,T)
   %finish

   %if ya # 0 %start
      R_A_X = Cosine (ya);  R_A_Y =           0;  R_A_Z = Sine (ya)
      R_B_X =           0;  R_B_Y =         One;  R_B_Z = 0
      R_C_X =  -Sine (ya);  R_C_Y =           0;  R_C_Z = Cosine (ya)
      MMult (R,T)
   %finish

   %if xa # 0 %start
      R_A_X =         One;  R_A_Y =           0;  R_A_Z = 0
      R_B_X =           0;  R_B_Y = Cosine (xa);  R_B_Z = Sine (xa)
      R_C_X =           0;  R_C_Y =  -Sine (xa);  R_C_Z = Cosine (xa)
      MMult (R,T)
   %finish

   Pp == P(0); Qp == Q(0)
   %for i = 0,1,Num Poly %cycle
      PL(i) == Q(i)
      PpV == Pp_V(1); QpV == Qp_V(1)
      Qp_Num = Pp_Num
      %for j = 1,1,Pp_Num %cycle
         Transform (T,PpV,QpV)
         QpV_X = QpV_X-Big; QpV_Y = QpV_Y-Big; QpV_Z = QpV_Z-Big
         PpV == PpV[1]; QpV == QpV[1]
      %repeat
      Pp == Pp[1]; Qp == Qp[1]
   %repeat
%end

%routine make unit vector(%record (rpt) %name vec)
    %real len
    Len=Sqrt(vec_X*vec_X+vec_Y*vec_Y+vec_Z*vec_Z)
    %if Len # 0 %start
       vec_X=vec_X/Len; vec_Y=vec_Y/Len; vec_Z=vec_Z/Len
    %finish
%end

%byte %fn Shade (%record (Pt) %name P1, P2, P3)
   %record (RPt) N, T1, T2
   %real Dot

   %integerfn Sign (%name N)
      !Returns the sign (-1 or 1) of a real by inspecting its top bit
      %result=-1 %if 16_80000000 & Integer(Addr(N)) # 0; %result=1
   %end

    T1_x=P1_x-P2_x; T1_y=P1_y-P2_y; T1_z=P1_z-P2_z            ;! T1 = P1-P2
    T2_x=P1_x-P3_x; T2_y=P1_y-P3_y; T2_z=P1_z-P3_z            ;! T2 = P1-P3
    N_X=T1_Y*T2_Z-T1_Z*T2_Y                         ;! N = Cross product of
    N_Y=T1_Z*T2_X-T1_X*T2_Z                         ;! T1 and T2, ie is the
    N_Z=T1_X*T2_Y-T1_Y*T2_X                         ;! normal of the poly. 
    Make unit vector(N)
    Dot = N_X*Light_X+N_Y*Light_Y+N_Z*Light_Z
    %if Sign (Dot) = - Sign (N_Z) %c
      %then %result = Ambient + IntPt ( (31-Ambient) * |Dot|)
    %result = Ambient
%end

%routine Load Trig Tables
   !Load scaled integer sine and cosine tables. Scaling factor is "one" (16384)
   %real Rads
   %integer Th
   %for Th = 0,1,359 %cycle
         Rads = Float (Th) * Rad
         Sine (Th) = Int (One * Sin (Rads))
         Cosine (Th) = Int (One * Cos (Rads))
   %repeat
%end

%routine Quick Sort (%short A, B)
   !Sort array PL from A to B inclusive on PL_DEPTH.
   %short l,u
   %record (Polt) %name Pp
   %while a < b %cycle
      l = a; u = b
      Pp == PL(u)
      -> Get
Up:   l = l + 1
      -> Got %if l = u
Get:  -> Up %unless Pp_Depth > PL(l)_Depth
      PL(u) == PL(l)
Down: u = u - 1
      -> Got %if l = u
      -> Down %unless Pp_Depth < PL(u)_Depth
      PL(l) == PL(u)
      -> Up
Got:  PL(u) == Pp
      l = l - 1
      u = u + 1
      %if l - a > b - l %then Quick Sort (u,b) %and b = l %c
                        %else Quick Sort (a,l) %and a = u
   %repeat
%end

%routine Load data
   %byte Col = White << 5, Col2
   %real A
   %integer i,j,c
   %integer hlen, type, wid, ht
   %integer PtNum
   %record (Pt) %array Pn (1:PMax)
   %record (Pt) %name Pp
   %record (Polt) %name Pt
   %short %array Ad ('A':'z')
   %integer dummy

   %routine rshort(%integername i)
      %integer a,b
      readsymbol(a); readsymbol(b)
      i=(a<<8+b)&16_FFFF
   %end

   !Load file.

   PrintString ("Opening ".File."... ")
   Open Input (3,File); Select Input (3)
   set input(46)
   rshort(i)
   set input(0)
   NumPoly = -1
   PtNum = 1
   %if i=16_8516 %start ;!IFF format magic number at position 46
     printline("IFF format")
     rshort(hlen); rshort(type); rshort(ht); rshort(wid)
     hlen=hlen*2
     set input(hlen)
     %if ht * wid > PMax %start
        printline("Can't cope with > ".itos(pmax,-1)." points")
        %stop
     %elseif type & 16_c0 # 0
        printline("Can't cope with compressed files")
        %stop
     %else
        ad('A') = ptnum-1
        %for i=1,1,ht %cycle
           %for j=1,1,wid %cycle
              readsymbol(c)
              pp == Pn(PtNum)
              Pp_x = (i-ht)*100; Pp_y = (j-wid)*100; Pp_z = c*3
              PtNum = PtNum + 1
           %repeat
        %repeat
     %finish
     write(PtNum-1,0); printstring(" points, and ")

     %for i=0,1,ht-2 %cycle
        k = i * wid
        %for j=0,1,wid-2 %cycle
           numpoly=numpoly+1
           pt == P(NumPoly)
           q(numpoly)_col = col
           pt_num = 4
           pt_v(1) = Pn(k+1)
           pt_v(2) = Pn(k+1+1)
           pt_v(3) = Pn(k+wid+1+1)
           pt_v(4) = Pn(k+wid+1)
           k = k + 1
        %repeat
     %repeat
     closeinput
     selectinput(0)
     write(numpoly+1, -1); printline(" polygons read in"); newline
     prompt("Viewing parameters:")
     read(sp_cx); read(sp_cy); read(sp_dist)
     read(xa); read(ya); read(za)
   %else ;!P. Read format
      Read Symbol (j) %until j = '#'
      %cycle
         Read Symbol (j) %until j # ' ' %and j # NL
         %exit %if j = '$'
         Ad (j) = PtNum - 1
         %cycle
            Read Symbol (j) %until j = ':' %or j = '$'
            %exit %if j = '$'
            Pp == Pn(PtNum)
            Read (A); Pp_X = Int (f128*A)
            Read (A); Pp_Y = Int (f128*A)
            Read (A); Pp_Z = Int (f128*A)
            PtNum = PtNum + 1
         %repeat
      %repeat
      Write(PtNum,0);PrintString (" Points, and ")
      Read Symbol (j) %until j = '#'
   
      %cycle
         Read Symbol (j) %until j = ':' %or j = '$' %or j = '>'
         %exit %if j = '$'
         %if j = '>' %start
            Read (Col); %if Col = Invisible %thenc
                        Read (Col2) %and Col2 = Col2 << 5 %else Col = Col << 5
            %continue
         %finish
         NumPoly = NumPoly + 1
         Pt == P(NumPoly)
         Q(NumPoly)_Col = Col
         Q(NumPoly)_Col2 = Col2 %if Col = Invisible
         Read (Pt_Num)
         %for j = 1,1,Pt_Num %cycle
            ReadSymbol (i) %until i # ' ' %and i # NL
            Read (k)
            k = k + Ad (i)
            Pt_V(j) = Pn(k)
         %repeat
      %repeat
      Write(NumPoly+1,0);Printline (" Polygons read in"); newline
   
      Read Symbol (j) %until j = '#'
      Read (dummy)
      Read (Sp_CX); Read (Sp_CY); Read (Sp_Dist)
      Read (XA); Read (YA); Read (ZA)
   Close Input
   %finish
   Select Input (0)
   %if xa >= 360 %then xa = xa - 360 %elseif xa < 0 %then xa = xa + 360
   %if Ya >= 360 %then Ya = Ya - 360 %elseif Ya < 0 %then Ya = Ya + 360
   %if Za >= 360 %then Za = Za - 360 %elseif Za < 0 %then Za = Za + 360
%end

%routine Up
   PrintSymbol(27);PrintSymbol('A')
   PrintSymbol(13);PrintSymbol(27);PrintSymbol('t')
%end
 
%routine Set up Stars
   %integer i
   StB = Addr(Stars(1,1))
   StT = Addr(Stars(MaxStars,2))
   %for i = 1,1,Max Stars %cycle
      Stars (i,1) = Random Int (1,686)
      Stars (i,2) = Random Int (1,510)
   %repeat     
%end

%routine Draw Body
   %integer i,j,CX,CY

   %routine plot polys(%integer col)
      %integer j
!!{t}   printstring("Polys   "); write(col, -1); newline
      {set} colour(col)
      Poly (PV(j)_X//SC+CX, PV(j)_Y//SC+CY) %for j = 1,1,Qp_Num
      Close Poly
   %end

   %routine plot outlines(%integer col)
     %integer j
!!{t}  printstring("Outlines"); write(col, 3); newline
     {set} colour(col)
     %for j=1,1,Qp_Num-1 %cycle
        Line(PV(j)_X//SC+CX,PV(j)_Y//SC+CY,PV(j+1)_X//SC+CX,PV(j+1)_Y//SC+CY) 
     %repeat
     Line(PV(1)_X//SC+CX,PV(1)_Y//SC+CY,PV(Qp_Num)_X//SC+CX,PV(Qp_Num)_Y//SC+CY)
   %end

%const %integer Frame Addr = 16_E00000
@Frame Addr %integerarray Frame(0:32767)

   %if Show Stars = True %start
      Half Clear (DS>>9)
      {set} colour(white)
      *Movea.l StB,a1
StLp:
      *Move.w (a1)+,xp
      *move.w (a1)+,d0
      *add.w DS,d0
      *Move.w d0,yp
      Frame (yp<<5+xp>>5)=1<<(31-xp&31)
      *cmpa.l StT,a1
      *ble StLp
   %else
      {set} Colour (Background)
      Fill (0,DS,687,511+DS)
   %finish

   OffSet (0,DS) %if Show = True
   CX = Sp_CX
   CY = Sp_CY + DS
   %if Hidden = True %start
      %if ReCalc = True %start
         Qp == Q(0)
         %for i = 0,1,NumPoly %cycle
            PV == Qp_V
            Max = PV(1)_Z
            %for j = 1,1,Qp_Num %cycle
               Max = PV(j)_Z %if PV(j)_Z > Max
            %repeat
            Qp_Depth = Max
            Qp == Qp[1]
         %repeat
         Quick Sort (0, Num Poly)
      %finish
      %for i = 0,1,NumPoly %cycle
         Qp == PL(i)
         PV == Qp_V
         %if Shading = True %start
            %if Qp_Num >= 3 %and Qp_Col # Invisible %start
               %if Qp_Col = Black %then Plot Polys(Black) %elsec
                  Plot Polys(Qp_Col+Shade(PV(1), PV(2), PV(3)))
            %finish

            %if Qp_Col = Invisible %start
               Plot Outlines(Qp_Col2+Shade(PV(1), PV(2), PV(3)))
            %elseif Shade Line = True
               Plot Outlines(Shade Line Col)
            %finish

         %else
            %if Qp_Num >= 3 %and Qp_Col # Invisible %start
               Plot Polys(Hidden Poly Col)
            %finish

            %if Qp_Col = Invisible %then Plot Outlines(Qp_Col2>>5) %elsec
            Plot Outlines(Hidden Line Col)
         %finish
      %repeat
   %else
      Qp == Q(0)
      %for i = 0,1,Num Poly %cycle
         PV == Qp_V
         Plot Outlines(Wire Col)
         Qp == Qp[1]
      %repeat
   %finish
   OffSet (0,DS) %unless Show = True
   DS = 512 - DS
!!  !Display colour map at LHS of screen
!!  %for i=0,1,255 %cycle
!!     {set} colour(i)
!!     fill(0,i*2, 10, i*2+2)
!!{t}  printstring("Fill    "); write(i, 3); newline
!!  %repeat
%end

%routine flush
   %cycle; %repeat %until Test Symbol = -1
%end

Setup
VClear
Set Terminal Mode (No Page)
Initialise Random
Set up Stars
File = CliParam
Load Trig Tables
newline; Printline ("General (Depth Sorting) Polygons Program"); newline
Stahrt:
   PrintSymbol(13)
   Prompt("File: ")
   flush
   Read Line(File) %while file = ""
Clear All
newline
Printline ("General (Depth Sorting) Polygons Program"); newline
Printline("MsR,L,M = Rotate X,Y,Z, or any combination of buttons")
Printline("Move Mouse to move shape, if Moving option selected")
Printline("a = Enter Increment Angle     ' '  = Negate Current Angle")
Printline("v = Move Towards Shape          b  = Move Away from Shape")
Printline("c = Enter X,Y Coordinates       r  = Enter angles X,Y,Z")
Printline("h = Hidden Line On/Off          s  = Shading On/Off")
Printline("z = Shade Line On/Off           l  = Enter Light Vector")
Printline("d = Change Distance             i  = Change Distance Inc")
Printline("m = Moving On/Off               f  = Enter File Name")
Printline("q = Drawing Visiblity On/Off    g  = Toggle Stars or Blue"); newline
load data
ReCalc = Hidden
Len = Sqrt(Lx*Lx + Ly*Ly + Lz*Lz)
Light_X = Lx/Len; Light_Y = Ly/Len; Light_Z = Lz/Len
%for i = 1,1,7 %cycle
   k = 32*i
   Mix Colour (k+j, (i&1)*j, (i&2)>>1*j, (i&4)>>2*j) %for j = 0,1,31
%repeat
mix colour (9,6,5,11)

mousex = 0; mousey = 0
convert
DS = 512
Sc = Sp_Dist { >> 1
Rotate (xa,ya,za)
Draw Body
flush
%cycle
   Changing = False
   ReCalc = False
   %cycle
      PrintSymbol(13);PrintSymbol(27);PrintSymbol('t')
      MB = Get Mouse
      %cycle
         ii = Test Symbol
      %repeatuntil ii<0 %or ' '<=ii<='z'

      %if MB # 0 %start
         %if MB & 1 = 1 %start
            xa = xa + Ang
            %if xa >= 360 %then xa = xa - 360 %elseif xa < 0 %then xa = xa + 360
         %finish
         %if MB & 2 = 2 %start
            ya = ya + Ang
            %if ya >= 360 %then ya = ya - 360 %elseif ya < 0 %then ya = ya + 360
         %finish
         %if MB & 4 = 4 %start
            za = za + Ang
            %if za >= 360 %then za = za - 360 %elseif za < 0 %then za = za + 360
         %finish
         Changing = True; ReCalc = True
         Rotate (xa,ya,za)
      %finish
      -> Nex %if ii = -1
      PrintSymbol(ii); PrintString ("...")
      -> TD(ii)

      TD('r'):
         PrintSymbol(13);PrintSymbol(27);PrintSymbol('t')
         flush
         Prompt ("X Angle (Currently ".Itos(Xa,0).") : ")
         read(Xa) %and Up %until -359 <= Xa <= 359
         Xa = Xa + 360 %if Xa < 0
         Prompt ("Y Angle (Currently ".Itos(Ya,0).") : ")
         read(Ya) %and Up %until -359 <= Ya <= 359
         Ya = Ya + 360 %if Ya < 0
         Prompt ("Z Angle (Currently ".Itos(Za,0).") : ")
         read(Za) %and Up %until -359 <= Za <= 359
         Za = Za + 360 %if Za < 0
         flush
         Changing = True
         ReCalc = True
         Rotate (xa,ya,za)
         -> Nex

      TD(' '):
         Ang = -Ang
         -> Nex

      TD('f'):
         File = ""
         -> Stahrt

      TD('m'):
         Moving = 1 - Moving; Changing = Moving
         -> Nex

      TD ('q'):
         Show = 1 - Show
         flush
         Changing = Show           {** ie: only Change if we are rebuilding
         -> Nex

      TD('s'):
         Shading = 1-Shading
         ReCalc = True %if Hidden = False %and Shading = True
         Hidden = True %if Shading = True
         Changing = True
         -> Nex

      TD('g'):
         Show Stars = 1 - Show Stars
         %if Show Stars = True %then Half Clear ((Ds-1)>>9)
         Changing = True
         -> Nex

      TD('z'):
         Shade Line = 1-Shade Line
         Changing = Shading         {** ie: only Change if we are shading
         -> Nex

      TD('h'):
         Hidden = 1-Hidden; ReCalc = Hidden
         Shading = False %if Hidden = False
         Changing = True
         -> Nex

      TD('l'):
         PrintSymbol(13);PrintSymbol(27);PrintSymbol('t')
         flush
         Prompt ("Light_X: ");read(light_x);Up
         Prompt ("Light_Y: ");read(light_Y);Up
         Prompt ("Light_Z: ");read(light_Z);Up
         make unit vector(light)
         Changing = True
         flush
         -> Nex

      TD('a'):
         PrintSymbol(13);PrintSymbol(27);PrintSymbol('t')
         flush
         Prompt ("Increment Angle (Currently ".Itos(Ang,0).") : ");read (ang);Up
         flush
         -> Nex

      TD('i'):
         PrintSymbol(13);PrintSymbol(27);PrintSymbol('t')
         flush
         Prompt ("Distance Increment (Currently ".Itos(Di,0).") : ")
         read (Di);Up
         flush
         -> Nex

      TD('d'):
         PrintSymbol(13);PrintSymbol(27);PrintSymbol('t')
         flush
         Prompt ("Distance (Currently ".Itos(Sc,0).") : ");read (Sc);Up
         Changing = True
         flush
         -> Nex

      TD('c'):
         PrintSymbol(13);PrintSymbol(27);PrintSymbol('t')
         flush
         Prompt ("CentreX (Currently ".Itos(Sp_Cx,0).") : ");read (sp_cx);Up
         Prompt ("CentreY (Currently ".Itos(Sp_CY,0).") : ");read (sp_cY);Up
         Changing = True
         flush
         -> Nex

      TD('v'):
         Sc = Sc - Di %unless Sc <= Di
         Changing = True
         flush
         -> Nex

      TD('b'):
         Sc = Sc + Di
         Changing = True
         flush
         -> Nex

      TD(*):
         ii = -1

      Nex: 
      %if Moving = True %start
         Convert
         i = mx - ox; j = my - oy
         sp_cx = (sp_cx + i) & 1023
         sp_cy = (sp_cy + j) & 1023
         ii = 1 %if i # 0 %or j # 0
         Changing = True
      %finish
   %repeat %until MB # 0 %or ii # -1

   Draw Body %if Changing = True

%repeat
%endofprogram