我有一些汇编代码可以使我的 MS-DOS 游戏的屏幕淡出它有效，但它不断循环

如何解决我有一些汇编代码可以使我的 MS-DOS 游戏的屏幕淡出它有效，但它不断循环

我正在用 C 和汇编为 MS-DOS 制作游戏（我打算用 DOSBox 或我自己的修改分发游戏）。我大部分图形代码都在汇编中，这是一种我较弱的语言，但我认为它使用起来很方便，因为它能够将事物更改为如此精细的级别（包括诸如图形调色板等）。

但是，我的代码基于从一些旧的 16 位汇编源代码中找到的淡出函数，我正在尝试将其转换为 32 位汇编。

我让代码工作了，但是，它不断重复循环而不是继续代码。

AFObeg  equ [bp+4]
AFOcnt  equ [bp+4+2]

proc FadeOut_ near
  push  ebx
  push  ecx
  push  edx
  mov   ebp,esp
  push  ds
  push  esi
  push  edi

  push  ds           ; get data segment into es
  pop  es
  mov  edx,offset _WorkPalette
  push  edx          ; save offset of opal
  xor  ebx,ebx
  mov  ecx,100h
  mov  eax,1017h    ; bios read dac registers function
  int  10h           ; read the palette registers into opal
  pop  edi           ; offset of opal,was in dx!
  mov  eax,AFObeg   ; get offset of first palette byte to
  mov  ebx,3        ; be processed
  mul  ebx
  add  edi,eax      ; adjust offset into opal
  mov  eax,AFOcnt   ; find the number of bytes to be processed
  mov  ebx,3
  mul  ebx           ; leave it in ax
  mov  ecx,64       ; 64 passes through fade loop
o_fade_loop:
  push  ecx          ; save the fade loop counter
  push  edi          ; save offset of first byte processed in
  mov  bl,cl        ; we'll use the pass number as a threshold
  mov  ecx,eax      ; load number of bytes to process into cx
o_pal_cmp_loop:
  cmp  bl,es:[edi]  ; start decrementing when palette value
  jnz  o_no_dec      ; is equal loop count (it will stay equal
  dec  BYTE PTR es:[edi]  ; to loop count for the rest of this pass)
o_no_dec:
  inc  edi
  loop o_pal_cmp_loop       ; do the next byte

  mov  ebx,esp      ; need the stack pointer for a moment
  mov  di,ss:[ebx]  ; restore offset into pal without popping
  mov  ecx,AFOcnt   ; number of triplets to process
  push  eax          ; need to use ax for port i/o

  mov  edx,03DAh    ; CRT controller input status 1 register
o_vbi_1:
  in  al,dx         ; watch vertical blanking bit
  test  al,08h       ; wait for it to clear to make sure
  jnz o_vbi_1        ; we're not in a blanking interval
o_vbi_2:
  in  al,dx         ; now wait for the start of the
  test  al,08h       ; next blanking interval
  jz  o_vbi_2

  mov  ah,AFObeg    ; get first register to process into ah
  mov  dx,03c8h     ; DAC palette index register
o_pal_load_loop:
  mov  al,ah        ; get next palette number to write
  out  dx,al        ; write the register number to the dac
  inc  dx            ; address dac data register
  mov  al,BYTE PTR es:[di] ; get first byte of triplet
  out  dx,al        ; write it to the dac data register
  inc  edi           ; point to second byte
  mov  al,BYTE PTR es:[di] ; get second byte of triplet
  out  dx,al        ; write it to the dac data register
  inc  edi           ; point to third byte
  mov  al,BYTE PTR es:[di] ; get third byte of triplet
  out  dx,al        ; write it to the dac data register
  inc  edi           ; point to first byte of next triplet
  dec  edx           ; address the da21c index register
  inc  ah            ; point to next palette register
  loop o_pal_load_loop      ; process next triplet

  pop  eax           ; restore ax
  pop  edi           ; restore the offset into pal
  pop  ecx           ; restore the fade loop counter
  loop o_fade_loop   ; do the next pass through the fade loop

  pop  edi
  pop  esi
  pop  ds
  pop  ebp
  ret
endp ;end of the fade out function

如果大家还有什么问题，我会很乐意回答的。

编辑：对于那些想知道原始代码是什么样子的人，这里是：

AFObeg  equ [bp+ABASE]
AFOcnt  equ [bp+ABASE+2]

PBEGIN _FadeOut
    push    bp
    mov bp,sp
    push    ds
    push    si
    push    di

    push    ds        ; get data segment into es
    pop es
    mov dx,offset DGROUP:_WorkPalette
    push    dx        ; save offset of opal
    xor bx,bx
    mov cx,100h
    mov ax,1017h     ; bios read dac registers function
    int 10h       ; read the palette registers into opal
    pop di        ; offset of opal,was in dx!
    mov ax,AFObeg    ; get offset of first palette byte to
    mov bx,3         ; be processed
    mul bx
    add di,ax        ; adjust offset into opal
    mov ax,AFOcnt    ; find the number of bytes to be processed
    mov bx,3
    mul bx        ; leave it in ax
    mov cx,64        ; 64 passes through fade loop
o_fade_loop:
    push    cx        ; save the fade loop counter
    push    di        ; save offset of first byte processed in
    mov bl,cl        ; we'll use the pass number as a threshold
    mov cx,ax        ; load number of bytes to process into cx
o_pal_cmp_loop:
    cmp bl,es:[di]   ; start decrementing when palette value
    jnz o_no_dec      ; is equal loop count (it will stay equal
    dec BYTE PTR es:[di]  ; to loop count for the rest of this pass)
o_no_dec:
    inc di
    loop    o_pal_cmp_loop      ; do the next byte

    mov bx,sp          ; need the stack pointer for a moment
    mov di,ss:[bx]     ; restore offset into pal without popping
    mov cx,AFOcnt      ; number of triplets to process
    push    ax          ; need to use ax for port i/o

        mov dx,03DAh       ; CRT controller input status 1 register
o_vbi_1:
        in al,dx           ; watch vertical blanking bit
        test al,08h         ; wait for it to clear to make sure
        jnz o_vbi_1         ; we're not in a blanking interval
o_vbi_2:
        in al,dx           ; now wait for the start of the
        test al,08h         ; next blanking interval
        jz o_vbi_2

    mov ah,BYTE PTR AFObeg ; get first register to process into ah
    mov dx,03c8h       ; DAC palette index register
o_pal_load_loop:
    mov al,ah          ; get next palette number to write
    out dx,al          ; write the register number to the dac
    inc dx          ; address dac data register
    mov al,BYTE PTR es:[di] ; get first byte of triplet
    out dx,al           ; write it to the dac data register
    inc di           ; point to second byte
    mov al,BYTE PTR es:[di] ; get second byte of triplet
    out dx,al           ; write it to the dac data register
    inc di           ; point to third byte
    mov al,BYTE PTR es:[di] ; get third byte of triplet
    out dx,al           ; write it to the dac data register
    inc di           ; point to first byte of next triplet
    dec dx           ; address the dac index register
    inc ah           ; point to next palette register
    loop    o_pal_load_loop      ; process next triplet

    pop ax        ; restore ax
    pop di        ; restore the offset into pal
    pop cx        ; restore the fade loop counter
    loop    o_fade_loop   ; do the next pass through the fade loop



    pop di
    pop si
    pop ds
    pop bp
    ret
_FadeOut endp

这里是宏 ET.MAC 文件，其中定义了 ABASE 之类的内容

; MACRO FILE FOR EGA320 LIBRARY


IFDEF   _ML
    %OUT    LARGE MODEL

PBEGIN  MACRO   L
    PUBLIC  L
L   PROC    FAR
    ENDM

PEXTRN  MACRO   L
    EXTRN   L:FAR
    ENDM

ABASE   EQU 6       ;BASE STACK PTR UPON PROCEDURE ENTRY

ENDIF

IFDEF   _MC

PBEGIN  MACRO   L
    PUBLIC  L
L   PROC    NEAR
    ENDM

PEXTRN  MACRO   L
    EXTRN   L:NEAR
    ENDM

ABASE   EQU 4       ;BASE STACK PTR UPON PROCEDURE ENTRY

    %OUT    COMPACT MODEL

ENDIF


XMOV    MACRO A,B
    PUSH    B       ;XFER SOURCE
    POP A       ; TO DEST.
    ENDM


GEN MACRO OP,ARG
    IRP X,<ARG>
    OP  X
    ENDM
    ENDM


XSTM    MACRO S,O,D
    MOV WORD PTR D,O
    MOV WORD PTR D+2,S
    ENDM

但是为了避免使用该文件，我已经切换到只是将 ABASE 的值更改为 4 或 6，但它们仍然给出了相对相似的结果。

解决方法

对于淡入淡出循环，您使用 mov ecx,eax 加载计数。回顾 eax 从哪里获得它的值，我们找到了 mov eax,AFOcnt 指令。不过貌似AFOcnt只有16位，所以eax的上半部分会有垃圾值，会导致你的循环运行时间长。

使用 movzx eax,word ptr AFOcnt 将 eax 的上半部分清零（或者您可以使用 and 指令将其屏蔽）。

其他一些注意事项（不全面）：

• 您保存了 ds，但修改了 es
• 这个简单的淡入淡出代码会在淡入淡出时破坏颜色。只需稍加努力，即可重做淡入淡出，以保留每个红-绿-蓝分量的相对值，从而使颜色真正淡化为黑色。
• 您混合使用 16 位（[di]，函数参数）和 32 位 ([edi]) 寻址。这应该专门使用 32 位寻址。