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Fourspriter: Alternate Version
#3
I like this code. These are like PRINT routines, but optimized for a specialized task :!:
Here you are some optimizations:

Code:
;; A
             LD BC,6 ; 10
             EX DE,HL ; 4
             ADD HL,BC ; 11
             ; EX DE,HL ; 4
             ;inc      de
             ;inc      de
             ;inc      de
            ...
Since BC is later discarded, this can be replaced by
Code:
;; A
             LD HL, 6 ; 10
             ADD HL, DE ; 11
             ;inc      de
             ;inc      de
             ;inc      de
             ...
This sequence occurs twice in the code. If you could use subversion, we could insert this into the library code in 1.2.6 so we can work as a team, submitting patches, and so on. :roll: (If you don't know, I could show you svn basic usages)

Code:
; xpos--
             ld      hl, xpos
             ld      a, (hl)
             dec      a
             ld      (hl), a
This can be replaced by
Code:
; xpos--
             ld      hl, xpos
             dec    (hl)

Since this is an xpos-- ANSI C output code (Z88DK, I guess) :-)
I think all commented code should be also removed out and comments translated into English (I could also do this).
Also JR is slower than JP. Since this routine is speed-critical, I replaced the jr here:
Code:
ld      a,   (de)
         cp      99
         jp      z,   nxt3 ; <== JP is faster

And finally, function encapsulation optimization:
In order to call some asm functions from BASIC you do
Code:
SUB xxxx
    asm
       call asm_func
    end asm
END SUB
Using FASTCALL with no parameters is like having an inline asm function. So you could return with a simple RET. But instead of returning from XXXX, you can return directly from asm_func:
Code:
SUB FASTCALL xxxx
    asm
       JP asm_func ; <== JUMP to asm_func and return from there
    end asm
END SUB
Even better, you can do your asm functions directly callable both from ASM and BASIC contexts. Doing all of these changes, this is the resulting code:
Code:
#DEFINE BLACK 0
#DEFINE BLUE 1
#DEFINE RED 2
#DEFINE MAGENTA 3
#DEFINE GREEN 4
#DEFINE CYAN 5
#DEFINE YELLOW 6
#DEFINE WHITE 7
#DEFINE TRANSPARENT 8
#DEFINE CONTRAST 9
#DEFINE TRUE 1
#DEFINE FALSE 0

SUB fspInitialize (n as uByte, udgA as uByte, udgB as uByte, udgC as uByte, udgD as uByte,x as uByte,y as uByte)  'Initialize Sprite: n (sprite number 0-3);a,b,c,d (UDG number 0-20,99 means the sprite won't be printed)
IF n>3 OR (udgA>20 AND udgA<>99) or udgB>20 or udgC>20 or udgD>20 then return : END IF : REM Bounds checking - so a bad function call doesn't poke all over memory.
DIM targetAddr as uInteger
targetAddr=@fspDataStart+(48*n)
fspErase()
POKE targetAddr,udgA
targetAddr=targetAddr+1
POKE targetAddr,udgB
targetAddr=targetAddr+1
POKE targetAddr,udgC
targetAddr=targetAddr+1
POKE targetAddr,udgD
targetAddr=targetAddr+1
POKE targetAddr,x
targetAddr=targetAddr+1
POKE targetAddr,y
targetAddr=targetAddr+1
POKE targetAddr,x
targetAddr=targetAddr+1
POKE targetAddr,y
fspBufferAndDraw()
RETURN

fspDataStart:

REM This Section contains Fourspriter data and code that is called by other routines.

ASM
;; 16x16 Sprites moving a character each frame
;; Copyleft 2009 The Mojon Twins.
;; Pergreñado por na_th_an
;; Uses UDGs (it reads the address from the system variables).
;; It moves up to 4 sprites, preserving the backgrounds.

datap:                        ; each block is 48 bytes long. [This comment originally said 40 bytes, and it's clearly 48]
;; Sprite 1
udgs1:      defb   99,0,0,0      ; Four UDGs of the first sprite.
x_pos1:     defb   0            ; X position in chars.
y_pos1:     defb   0            ; Y position in chars.
cx_pos1:    defb   0            ; Previous X position in chars.
cy_pos1:    defb   0            ; Previous Y position in chars.
buffer1:    defb   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0         ; Background Gfx buffer.
attrs1:     defb   7,7,7,7      ; Sprite ATTRs
buffatrs1:  defb   0,0,0,0      ; Background Attr's buffer

;; Sprite 2
udgs2:      defb   99,0,0,0
x_pos2:     defb   0
y_pos2:     defb   0
cx_pos2:    defb   0
cy_pos2:    defb   0
buffer2:    defb   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
attrs2:     defb   7,7,7,7
buffatrs2:  defb   0,0,0,0

;; Sprite 3
udgs3:      defb   99,0,0,0
x_pos3:     defb   0
y_pos3:     defb   0
cx_pos3:    defb   0
cy_pos3:    defb   0
buffer3:    defb   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
attrs3:     defb   7,7,7,7
buffatrs3:  defb   0,0,0,0

;; Sprite 4
udgs4:      defb   99,0,0,0
x_pos4:     defb   0
y_pos4:     defb   0
cx_pos4:    defb   0
cy_pos4:    defb   0
buffer4:    defb   0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
attrs4:     defb   7,7,7,7
buffatrs4:  defb   0,0,0,0

;; General use coordinates
xpos:      defb    0
ypos:      defb    0
cxpos:     defb   0
cypos:     defb    0

;; Sprite control is done writing a certain number
;; in the Sprite's first UDG
;; If the first UDG is 99, it won't be printed

docopy:
borra_char:    
         call   get_scr_address   ; DirecciÎáÎõÎån (xpos, ypos) en BC
         ld      l,    c
         ld      h,    b         ; DirecciÎáÎõÎån (xpos, ypos) en HL        
        
         ld      a,   (de)
         ld      (hl), a
         inc      h
         inc      de
         ld      a,   (de)
         ld      (hl), a
         inc      h
         inc      de
         ld      a,   (de)
         ld      (hl), a
         inc      h
         inc      de
         ld      a,   (de)
         ld      (hl), a
         inc      h
         inc      de
         ld      a,   (de)
         ld      (hl), a
         inc      h
         inc      de
         ld      a,   (de)
         ld      (hl), a
         inc      h
         inc      de
         ld      a,   (de)
         ld      (hl), a
         inc      h
         inc      de
         ld      a,   (de)
         ld      (hl), a
         inc      h
         inc      de
        
         ret
        
;; Esta funciÎáÎõÎån devuelve en bc la direcciÎáÎõÎån de memoria
;; de la posiciÎáÎõÎån (xpos, ypos) en carÎáÎõÎÝcteres. ExtraÎáÎõÎádo de cÎáÎõÎådigo
;; por BloodBaz.

get_scr_address:
         push    de
         ld       a,   (xpos)
         and      31
         ld      c,   a
         ld      a,   (ypos)
         ld      d,   a
         and      24
         add      a,   64
         ld      b,    a
         ld      a,   d
         and      7
         rrca
         rrca
         rrca
         or      c
         ld      c,    a
         pop      de
         ret
              
;; Esta funciÎáÎõÎån devuelve en bc la direcciÎáÎõÎån de memoria
;; de la posiciÎáÎõÎån (xpos, ypos) dentro del archivo de atributos.
;; Adaptado de cÎáÎõÎådigo por Jonathan Cauldwell.

;; 010110YY YYYXXXXX

get_attr_address:
        
         ld      a,    (ypos)      ; Cogemos y
         rrca
         rrca
         rrca               ; La multiplicamos por 32
         ld      c,   a         ; nos lo guardamos en c
         and      3            ; ponemos una mascarita 00000011
         add      a,   88         ; 88 * 256 = 22528, aquÎáÎõÎá empieza el tema
         ld      b,   a         ; Hecho el bite superior.
         ld      a,   c         ; Nos volvemos a traer y * 32
         and      224            ; Mascarita 11100000
         ld      c,   a         ; Lo volvemos a poner en c
         ld      a,   (xpos)      ; Cogemos x
         add      a,    c         ; Le sumamos lo que tenÎáÎõÎáamos antes.
         ld      c,   a         ; Listo. Ya tenemos en BC la direcciÎáÎõÎån.
         ret
        
spare:      defb   85,85,85,85,85,85,85,85


;; Routine to save the background to the buffer

;borra_sprites:

; pointer = datap
; for (i = 0; i < 4; i ++) {
;    CX = *(pointer + 6)
;    CY = *(pointer + 7)
;    scr_address = get_scr_address (CX, CY);
;    for (j = 0; j < 8; j ++) {
;       *scr_address = *(pointer + 8 + j);
;      scr_address += 256;
;    }
;    scr_address = get_scr_address (CX+1, CY);
;    for (j = 0; j < 8; j ++) {
;       *scr_address = *(pointer + 16 + j);
;      scr_address += 256;
;    }
;    scr_address = get_scr_address (CX, CY+1);
;    for (j = 0; j < 8; j ++) {
;       *scr_address = *(pointer + 24 + j);
;      scr_address += 256;
;    }
;    scr_address = get_scr_address (CX+1, CY+1);
;    for (j = 0; j < 8; j ++) {
;       *scr_address = *(pointer + 32 + j);
;      scr_address += 256;
;    }
;    pointer += 40;
; }
fspEraseAsm:

         ld       de, datap      ;
         ld      b,   4         ;
i4chars2:   push   bc
        
         ;;
         ld      a,   (de)
         cp      99
         jr      z,   nxt2

         ;; A
         LD BC,6 ; 10
         EX DE,HL ; 4
         ADD HL,BC ; 11
         ; EX DE,HL ; 4
         ;inc      de
         ;inc      de
         ;inc      de
         ;inc      de
         ;inc      de
         ;inc      de
        
         ; Obtenemos xpos = CX
         ld      DE,   xpos
         ;ld      a,   (de)
         ;ld      (hl), a
         LDI
         ;inc    de
        
         ; Obtenemos ypos = CY
         ld      DE, ypos
         ;ld      a,   (de)
         ;ld      (hl), a
         ;inc    de
         LDI
         EX DE,HL
         ;; B
        
         ; Pintamos el primer char
         call   borra_char
                
         ; xpos++
         ld      hl, xpos
         inc      (hl)
        
         ;; C
        
         ; Pintamos el segundo char
         call   borra_char

         ; xpos --
         ld      hl, xpos
         ;ld      a, (hl)
         ;dec      a
         ;ld      (hl), a
         dec (hl)
         ; ypos ++
         ld      hl, ypos
         inc      (hl)
        
         ;; D
        
         ; Pintamos el tercer char
         call    borra_char

         ; xpos++
         ld      hl, xpos
         inc      (hl)
        
         ;; E

         ; Pintamos el cuarto char
         call   borra_char
        
         ;; attr
         inc      de
         inc      de
         inc      de
         inc      de
        
         ;;
        
         ; xpos --
         ld      hl, xpos
         dec (hl)
        
         ; ypos --
         ld      hl, ypos
         dec (hl)
              
         ;
         call   get_attr_address
        
         ;
         call   copyattrs
        
         ;
        
nxt2:      pop      bc
         djnz    i4chars2        
    
ret


copia_char:
         call   get_scr_address   ;
         ld      l,    c
         ld      h,    b         ;
         ld      a,   (hl)
         ld      (de), a
         inc      h
         inc      de
         ld      a,   (hl)
         ld      (de), a
         inc      h
         inc      de
         ld      a,   (hl)
         ld      (de), a
         inc      h
         inc      de
         ld      a,   (hl)
         ld      (de), a
         inc      h
         inc      de
         ld      a,   (hl)
         ld      (de), a
         inc      h
         inc      de
         ld      a,   (hl)
         ld      (de), a
         inc      h
         inc      de
         ld      a,   (hl)
         ld      (de), a
         inc      h
         inc      de
         ld      a,   (hl)
         ld      (de), a
         inc      h
         inc      de
        
         ret

fspBufferAndDrawAsm:
init_sprites:                

; pointer = datap
; for (i = 0; i < 4; i ++) {
;    X = *(pointer + 4);                           // A
;    Y = *(pointer + 5);
;    scr_address = get_scr_address (X, Y);               // B
;    for (j = 0; j < 8; j ++) {
;       *(pointer + 8 + j) = *scraddress;
;       scraddress += 256;
;    }
;    scr_address = get_scr_address (X+1, Y);            // C
;    for (j = 0; j < 8; j ++) {
;       *(pointer + 16 + j) = *scraddress;
;       scraddress += 256;
;    }
;    scr_address = get_scr_address (X, Y+1);            // D
;    for (j = 0; j < 8; j ++) {
;       *(pointer + 24 + j) = *scraddress;
;       scraddress += 256;
;    }
;    scr_address = get_scr_address (X+1, Y+1);            // E
;    for (j = 0; j < 8; j ++) {
;       *(pointer + 32 + j) = *scraddress;
;       scraddress += 256;
;    }
;    pointer = pointer + 40;
; }

         ld       de, datap      ;

         ld      b,   4         ;
i4chars:   push   bc
        
         ;;
         ld      a,   (de)
         cp      99
         jr      z,   nxt1

         ;; A
         LD HL, 4
         ADD HL, DE
        
         ld      DE,   xpos
         ;ld      a,   (de)
         ;ld      (hl), a
         ;inc    de
         LDI
        
         ld      DE, ypos
         LDI
         EX DE,HL
         inc    de
         inc    de
        
         ;; B
        
         ;
         call   copia_char
        
         ; xpos++
         ld      hl, xpos
         inc      (hl)
        
         ;; C
        
         ;
         call    copia_char

         ; xpos --
         ld      hl, xpos
         dec (hl)
        
         ; ypos ++
         ld      hl, ypos
         inc      (hl)
        
         ;; D
        
         ;
         call    copia_char

         ; xpos++
         ld      hl, xpos
         inc      (hl)
        
         ;; E
        
         ;
         call   copia_char
        

         ;; Now we point to the ATTR buffer,adding 4:
         inc      de
         inc      de
         inc      de
         inc      de
        
         ;;
        
         ; xpos --
         ld      hl, xpos
         dec (hl)
        
         ; ypos --
         ld      hl, ypos
         dec (hl)
         call   get_attr_address
        
         ld      l, c
         ld      h, b
         ld      bc, 32
        
         ; 1st character
         LDI  ; bc was loaded with 32 instead of 31
          ;to account for the BC-- this instruction has.
        
         ; 2nd character
         LDI
         add      hl,   bc ; we can get away with this
                   ; because BC++ as well as hl--

         ; 3rd character
         LDI
        
         ; 4th character
         LDI
         ; Fin del bucle
        
nxt1:    pop      bc
         djnz    i4chars
         ; ret - No! Go straight into Painting new sprites for speed.

        

;; Print sprites routine
;; UDGs are labeled from  0 to 21. The addres of the UDG is:
;; *(23675) + 256 * *(23676) + 8 * N
fspDrawAsm:
draw_sprites:
         ld       de, datap      ;
         ld      b,   4         ;
i4chars3:   push   bc
         ld      a,   (de)
         cp      99
         jp      z,   nxt3
         ;; copiar aquÎáÎõÎá "de" a un buffer
         call   charsabuff
         ; Obtenemos xpos
         ld      hl,   xpos
         EX DE,HL
         LDI

         ; Obtenemos ypos
         ld      DE, ypos
         LDI
         inc    HL ; de
         inc    HL ; de
         push   HL ; de
        
         ld      hl, bufchars
         call   getde
         call   docopy
         ; xpos++
         ld      hl, xpos
         inc      (hl)
         ; DirecciÎáÎõÎån del grÎáÎõÎÝfico
         ld      hl, bufchars+1
         ;inc      hl
         call   getde
         ; Pintamos el segundo char

         call   docopy
         ; xpos--
         ld      hl, xpos
         dec     (hl)
        
         ; ypos ++
         ld      hl, ypos
         inc      (hl)

         ; Graphic address
         ld      hl, bufchars+2
         call   getde

         ; Pintamos el tercer char
         call   docopy
         ; xpos ++
         ld      hl, xpos
         inc      (hl)

         ; Graphic address
         ld      hl, bufchars+3
         call    getde
        
         ; Pintamos el cuarto char
         call   docopy
                    
         pop      de
        
         ; de = de + 32
         ld      hl, 32
         add     hl, de
         ex      de, hl
        
         ;; attr
        
         ; xpos --
         ld      hl, xpos
         dec (hl)
        
         ; ypos --
         ld      hl, ypos
         dec(hl)    
         ;
         call   get_attr_address
        
         ;
         call   copyattrs
        
         inc      de
         inc      de
         inc      de
         inc      de            ;
        
nxt3:    pop      bc
         djnz    i4chars3
        
         ret


;; Esta funciÎáÎõÎån calcula la posiciÎáÎõÎån en memoria del UDG apuntado por
;; el nÎáÎõÎémero que estÎáÎõÎÝ en la direcciÎáÎõÎån hl.
        
getde:   ld      a, (hl)
         ld HL,(23675)
         ;;      HL = *(23675) + 256 * *(23676)
         rlca
         rlca
         rlca   ; a = N * 8
         ld      d, 0
         ld      e, a
         add      hl, de
         EX DE,HL
         ret


bufchars:   defb   0,0,0, 0      ;

charsabuff: ld      hl,   bufchars
         EX DE,HL
         LDI
         LDI
         LDI
         LDI
         EX DE,HL
         ret
                
copyattrs:   ld      l,    c
         ld      h,    b
         ld      bc, 31
         ld      a,   (de)
         ld      (hl), a         ; Primer carÎáÎõÎÝcter
         inc      hl
         inc      de          
         ld      a,    (de)  
         ld      (hl), a         ; Segundo carÎáÎõÎÝcter
         add      hl,   bc
         inc      de
         ld      a,   (de)
         ld      (hl), a         ; Tercer carÎáÎõÎÝcter
         inc      hl
         inc      de
         ld      a,    (de)
         ld      (hl), a         ; Cuarto carÎáÎõÎÝcter
         inc      de            ; Ahora de apunta a datap+48, o sea, al siguiente sprite.
         ret
END ASM
END SUB

REM FUNCTION ENCAPSULATION
REM This function is callable both from BASIC and ASM
SUB fastcall fspUpdate() : REM <= This name is used for CALL from BASIC
    asm
fspUpdateAsm:       ; <= This name is used for CALL from ASM
         update_coordinates:
         ld       de, datap      ; Apuntamos a la zona de datos
         ld      hl, datap      ; idem
         ld      b,   4         ; 4 iteraciones
i4chars4:   push   bc

         ;; Para cada sprite hay que hacer:
         ;; *(datap + 6) = *(datap + 4)
         ;; *(datap + 7) = *(datap + 5)
        
         inc      de
         inc      de
         inc      de
         inc      de
         ld      a, (de)         ; a = X
         inc      hl
         inc      hl
         inc    hl
         inc      hl
         inc      hl
         inc      hl
         ld      (hl), a         ; CX = a
                                                    
         inc    de
         ld      a, (de)         ; a = Y
         inc    hl
         ld      (hl), a         ; CY = a

         inc      hl
        
         ;; hl = hl + 40
         ld      bc, 40
         add      hl, bc
        
         ;; de = hl
         ld      d, h
         ld      e, l
        
         pop      bc
         djnz    i4chars4
         ; ret
END ASM
END SUB

SUB fspDisable (n as UByte)
IF n>3 then return : END IF
POKE @fspDataStart+48*n,99
end SUB

SUB fspCoord (n as uByte, x as uByte, y as uByte)   'Set sprite coords: n (sprite number);x,y (vertical,horizontal coords)
IF n>3 then return : END IF
DIM targetAddr as uInteger
targetAddr=@fspDataStart+4+48*n
POKE targetAddr,x
targetAddr=targetAddr+1
POKE targetAddr,y
rem targetAddr=targetAddr+1
rem POKE targetAddr,x
rem targetAddr=targetAddr+1
rem POKE targetAddr,y
END SUB

SUB fspAttrs (n as uByte, attra as uByte, attrb as uByte, attrc as uByte, attrd as uByte) 'Set sprite attrs: n (sprite number);a,b,c,d (UDG attrs)
IF n>3 then return : END IF
DIM targetAddr as uInteger
targetAddr=@fspDataStart+40+48*n
POKE targetAddr,attra
targetAddr=targetAddr+1
POKE targetAddr,attrb
targetAddr=targetAddr+1
POKE targetAddr,attrc
targetAddr=targetAddr+1
POKE targetAddr,attrd
END SUB

FUNCTION fspAttrByte(fspInk as uByte,fspPaper as uByte,fspBright as uByte, fspFlash as uByte) as uByte
    if fspInk > 7 OR fspPaper > 7 OR fspBright > 1 or fspFlash >1 then return 0: END IF: Rem bounds check
    return (fspFlash shl 7) + (fspBright shl 6) + (fspPaper shl 3) + fspInk
END FUNCTION

SUB fspAttr(n as uByte,fspInk as uByte,fspPaper as uByte,fspBright as uByte, fspFlash as uByte)
    if fspInk > 7 OR fspPaper > 7 OR fspBright > 1 or fspFlash >1 then return : END IF: Rem bounds check
    DIM attrByte as uByte
    attrByte=fspAttrByte(fspInk,fspPaper,fspBright,fspFlash)
    fspAttrs(n,attrByte,attrByte,attrByte,attrByte)
END SUB    

SUB FASTCALL fspErase()
  asm
  call fspEraseAsm
  end asm
END SUB


SUB FASTCALL fspBufferAndDraw()
asm
call fspBufferAndDrawAsm
end asm
END SUB


SUB FASTCALL fspRedraw()
asm
   halt
   ;REM Erase the sprites
   call fspEraseAsm
   ;REM Save background and
   ;REM print sprites
   call fspBufferAndDrawAsm
   ;REM update coordinates
   jp fspUpdateAsm
  
end asm
END SUB

REM below this is Apenao's Demo Program:

#include <sinclair.bas>
#include <memcopy.bas>
#include <keys.bas>


100 DIM gentle (0 to 3,0 to 7) AS uByte => {  { 15, 15, 15, 15, 15, 15, 13, 15} , _
     { 240, 144, 208, 208, 240, 240, 176, 240} , _
     { 15, 14, 63, 0, 0, 12, 26, 30} , _
     { 176, 112, 252, 0, 0, 48, 104, 120}}

110 POKE Uinteger 23675, @gentle(0,0)

    memcopy (0,16384,4092)
    LET gx=10:LET gy=10:let dx=3:let dy=3:let tx=6:let ty=6:let cx=18:let cy=18
    let dmx=1:let dmy=1:let tmx=-1:let tmy=-1:let cmx=1:let cmy=-1
    fspInitialize (0,0,1,2,3,gx,gy) : REM (sprite number, udgA, udgB,udgC,udgD, initial X co-ordinate, initial y-coordinate)                                                    
    fspInitialize (1,0,1,2,3,dx,dy)
    fspInitialize (2,0,1,2,3,tx,ty)
    fspInitialize (3,0,1,2,3,cx,cy)
  
    fspAttr(0,WHITE,MAGENTA,FALSE,FALSE) : REM (sprite number, ink, paper, bright, flash)
    fspAttr(1,YELLOW,BLACK,FALSE,FALSE)
    fspAttr(2,GREEN,BLUE,TRUE,FALSE)
    fspAttr(3,RED,WHITE,FALSE,FALSE)
  
DO
    PAUSE 2

    REM IF MultiKeys(X) <> X can be replaced by MultiKeys(X)
    IF MULTIKEYS(KEYO) and gx>0 THEN LET gx=gx-1: END IF
    IF MULTIKEYS(KEYP) and gx<30 THEN LET gx=gx+1:END IF
    IF MULTIKEYS(KEYQ) and gy>0 THEN LET gy=gy-1 :END IF
    IF MULTIKEYS(KEYA) and gy<22 THEN LET gy=gy+1: END IF

    let dx=dx+dmx:if dx=0 or dx=30 then let dmx=-dmx : END IF
    let dy=dy+dmy:if dy=0 or dy=22 then let dmy=-dmy: END IF
    let tx=tx+tmx:if tx=0 or tx=30 then let tmx=-tmx: END IF
    let ty=ty+tmy:if ty=0 or ty=22 then let tmy=-tmy: END IF
    let cx=cx+cmx:if cx=0 or cx=30 then let cmx=-cmx: END IF
    let cy=cy+cmy:if cy=0 or cy=22 then let cmy=-cmy: END IF

    fspCoord (0,gx,gy)
    fspCoord (1,dx,dy)
    fspCoord (2,tx,ty)
    fspCoord (3,cx,cy)

    fspRedraw()

loop
Look also at the MultiKeys checking at the end of the above code (click on the Expand button to see it in a greater window). The following are equivalent:
Code:
IF Multikeys(KEYO) <> 0 THEN
    ...
    END IF
    IF MultiKeys(KEYO) THEN : REM This comparison is faster and take less memory
    ...
    END IF
The 1st IF should be transformed into the second one automatically, but I haven't implemented such optimization yet.
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