问题
I have a code that shows a PCX using assembly
By its width
Example image 320x200 x=0, y=0
But if X (StartPictX) and Y (StartPictY) are unequal to 0, it ruins the picture.
And I need to fix that...
The original code:
;--------------------------------------
; Load and show file *.PCX 320x200x256
;
;--------------------------------------
IDEAL
MODEL large
P386
MACRO SHOWPCX StartX, StartY, fName
mov ax, [StartX]
mov [Point_X], ax
mov ax, [StartY]
mov [Point_Y], ax
mov dx, offset fName
call ShowPCXFile
ENDM SHOWPCX
STACK 256
DATASEG
ErrorReadingFile DB 'Can not open file$'
FileName1 DB 'mouse.pcx',0
FileName DW ? ; offset file name for current file
FileHandle DW ?
FileSize DW ?
ImageSizeInFile DW ?
ImageWidth DW ?
ImageHeigth DW ?
PaletteOffset DW ?
Point_X DW ?
Point_Y DW ?
Color DB ?
StartPictX DW ?
StartPictY DW ?
SEGMENT FILEBUF para public 'DATA'
DB 65200 DUP(?)
ENDS
CODESEG
Start:
mov ax, @data
mov ds, ax
mov ax, 0013h
int 10h
; -----------------= Show Pic1 =----------------
mov [StartPictX], 0
mov [StartPictY], 0
SHOWPCX StartPictX, StartPictY, FileName1
mov ah,00h
int 16h
mov ah,00h
mov al,03h
int 10h
Exit:
mov ax,04c00h
int 21h
;-------------------------------------------
; ReadPCXFile - read PCX file into FILEBUF
;-------------------------------------------
; Input:
; File name
; Output:
; File into FILEBUF
; Registers
; AX, BX, CX, DX, DS
;-------------------------------------------
PROC ReadPCXFile Near
pusha
;----- Initialize variables
mov [FileHandle],0
mov [FileSize],0
;----- Open file for reading
mov ah, 3Dh
mov al, 0
; mov DX,offset FileName
int 21h
jc @@Err
mov [FileHandle],AX ; save Handle
;----- Get the length of a file by setting a pointer to its end
mov ah, 42h
mov al ,2
mov bx, [FileHandle]
xor cx, cx
xor dx, dx
int 21h
jc @@Err
cmp dx,0
jne @@Err ;file size exceeds 64K
;----- Save size of file
mov [FileSize], ax
;----- Return a pointer to the beginning of the file
mov ah, 42h
mov al, 0
mov bx, [FileHandle]
xor cx, cx
xor dx, dx
int 21h
jc @@Err
;----- Read file into FILEBUF
mov bx, [FileHandle]
pusha
push ds
mov ax,FILEBUF
mov ds, ax
xor dx, dx
mov cx, 65200
mov ah, 3Fh
int 21H
pop ds
popa
jc @@Err
;----- Close the file
mov ah, 3Eh
mov bx,[FileHandle]
int 21H
jc @@Err
popa
ret
;----- Exit - error reading file
@@Err: ; Set text mode
mov ax, 3
int 10h
mov dx, offset ErrorReadingFile
mov ah, 09h
int 21h
jmp Exit
ENDP ReadPCXFile
;-------------------------------------------
; ShowPCXFile - show PCX file
;-------------------------------------------
; Input:
; File name
; Output:
; The file
; Registers
; AX, BX, CX, DX, DS
;-------------------------------------------
PROC ShowPCXFile Near
pusha
call ReadPCXFile
mov ax, FILEBUF
mov es, ax
;----- Set ES:SI on the image
mov si, 128
;----- Calculate the width and height of the image
mov ax, [es:42h]
mov [ImageWidth], ax
dec [ImageWidth]
mov ax, [es:0Ah]
sub ax, [es:6]
inc ax
mov [ImageHeigth], ax
;----- Calculate the offset from the beginning of the palette file
mov ax, [FileSize]
sub ax, 768
mov [PaletteOffset], ax
call SetPalette
mov ax, [FileSize]
sub ax, 128+768
mov [ImageSizeInFile], ax
xor ch, ch ; Clear high part of CX for string copies
push [StartPictX] ; Set start position
pop [Point_x]
push [StartPictY]
pop [Point_y]
NextByte:
mov cl, [es:si] ; Get next byte
cmp cl, 0C0h ; Is it a length byte?
jb normal ; No, just copy it
and cl, 3Fh ; Strip upper two bits from length byte
inc si ; Advance to next byte - color byte
mov al, [es:si]
mov [Color], al
NextPixel:
call PutPixel
cmp cx, 1
je CheckEndOfLine
inc [Point_X]
loop NextPixel
jmp CheckEndOfLine
Normal:
mov [Color], cl
call PutPixel
CheckEndOfLine:
mov ax, [Point_X]
sub ax, [StartPictX]
cmp ax, [ImageWidth]
;----- [Point_X] - [StartPictX] >= [WidthPict]
jae LineFeed
inc [Point_x]
jmp cont
LineFeed:
push [StartPictX]
pop [Point_x]
inc [Point_y]
cont:
inc si
cmp si, [ImageSizeInFile] ; End of file? (written 320x200 bytes)
jb nextbyte
popa
ret
ENDP ShowPCXFile
;-------------------------------------------
; PutPixel - draw pixel
;-------------------------------------------
; Input:
; x - Point_x, y - Point_y, Color - color
; Output:
; The pixel
; Registers
; AX, BH, CX, DX
;-------------------------------------------
PROC PutPixel near
pusha
mov bh, 0h
mov cx, [Point_x]
mov dx, [Point_Y]
mov al, [color]
mov ah, 0ch
int 10h
popa
ret
ENDP PutPixel
;-------------------------------------------
; SetPalette - change palette from 0-255 to from 0-63
;-------------------------------------------
; Input:
; PaletteOffset
; Output:
; New palette
; Registers
; AX, BX, CX, DX, SI, ES
;-------------------------------------------
SetPalette:
pusha
mov cx, 256*3
mov si, [PaletteOffset]
NextColor:
shr [byte es:si], 2
inc si
loop NextColor
mov dx, [PaletteOffset]
mov ax, 1012h
mov bx, 00h
mov cx, 256d
int 10h
popa
ret
End Start
I realized the problem is the width of the image. It continues to line pixels until we reach the width of the image and then add to Y.
I tried to change it but didn't succeed:
CheckEndOfLine:
mov ax, [Point_X]
;sub ax, [StartPictX]
cmp ax, 320
jae LineFeed
inc [Point_x]
inc si
jmp cont
LineFeed:
push [StartPictX]
pop [Point_x]
inc [Point_y]
mov bx,320
sub bx,[StartPictX]
@@lop:
mov cl, [es:si] ; Get next byte
cmp cl, 0C0h ; Is it a length byte?
jb nor
and cl, 3Fh ; Strip upper two bits from length byte
add si,cx
sub bx,cx
jmp next
nor:
inc si
dec bx
next:
cmp bx,1
jg @@lop
cont:
cmp si, [ImageSizeInFile] ; End of file? (written 320x200 bytes)
jb nextbyte
popa
ret
I really need help :)
Tnx for the helpers
回答1:
The calculation of the ImageSizeInFile is correct but your code uses this info as if it represented an address!. I suggest you rename the variable and use next calculation:
mov ax, [FileSize]
sub ax, 768
mov [ImageEndAddressInFile], ax
You need to calculate the ImageWidth correctly, just like you did for the ImageHeight. The number of bytes in 1 scanline does not necessarily correspond to the image width in pixels, especially in case of compression!
mov ax, [es:0008h] ; X2
sub ax, [es:0004h] ; X1
inc ax
mov [ImageWidth], ax
mov ax, [es:000Ah] ; Y2
sub ax, [es:0006h] ; Y1
inc ax
mov [ImageHeight], ax
Your current program increments the X position Point_x only conditionally. This is not fine. For every pixel that you've processed, you must always have inc [Point_x].
NextByte:
mov cl, [es:si] ; Get next byte
inc si
cmp cl, 0C0h ; Is it a length byte?
jb Normal ; No, just copy it
and cx, 003Fh ; Strip upper two bits from length byte
mov al, [es:si] ; The color
inc si
mov [Color], al
jcxz CheckEndOfLine ; Could exist this one!
NextPixel:
call PutPixel
inc [Point_X]
loop NextPixel
jmp CheckEndOfLine
Normal:
mov [Color], cl
call PutPixel
inc [Point_x]
CheckEndOfLine:
mov ax, [Point_X]
sub ax, [StartPictX] ; Number of processed pixels
cmp ax, [ImageWidth] ; Image width measured in pixels
jb Cont
LineFeed:
push [StartPictX]
pop [Point_x]
inc [Point_y]
Cont:
cmp si, [ImageEndAddressInFile]
jb NextByte
Now we can address the issue of freely selecting StartPictX and StartPictY.
An easy solution is to process the image data fully (just as if the image would snugly fit the screen) and have the PutPixel procedure clip off points that fall outside of the screen.
PROC PutPixel near
cmp [Point_y], 200
jnb IsOutside
cmp [Point_x], 320
jnb IsOutside
pusha
mov dx, [Point_y]
mov cx, [Point_x]
mov bh, 0
mov al, [Color]
mov ah, 0Ch
int 10h
popa
IsOutside:
ret
ENDP PutPixel
A mixed solution is somewhat better. Always presenting PutPixel a valid Y-coordinate:
LineFeed:
push [StartPictX]
pop [Point_x]
inc [Point_y]
cmp [Point_y], 200 <<<<<
jnb Done <<<<<
Cont:
cmp si, [ImageEndAddressInFile]
jb NextByte
Done:
and
PROC PutPixel near
cmp [Point_x], 320
jnb IsOutside
pusha
mov dx, [Point_y]
mov cx, [Point_x]
mov bh, 0
mov al, [Color]
mov ah, 0Ch
int 10h
popa
IsOutside:
ret
ENDP PutPixel
来源：https://stackoverflow.com/questions/61410379/dont-understand-whats-wrong-with-my-pcx-code