CSC231 makegreyBmp.asm

;;; makegreyBmp.asm
;;; D. Thiebaut
;;; This program reads a bmp file into memory, make each pixel
;;; grey, and store the resulting image back in the original
;;; picture.
;;; 
%include "mytools2.inc"		; for basic printing to the screen
%include "fileio2.inc"		; for basic file operations
		
%assign SYS_EXIT	1
%assign MAXPIXEL	5000000

%assign RED             2
%assign GREEN           1
%assign BLUE            0       



;;; ---------------------------------------------------------
;;; data segments
;;; ---------------------------------------------------------
        section .data
errorMsg db     "Error accessing file!",0x0A
errorLen equ    $-errorMsg

	section	.bss
filename resb   255		; reserve 255 chars for filename
handle   resd	1		; file descriptor
noRead	 resd	1		; contains number of bytes read
lWidth	 resd	1		; the line width rounded to the nearest
      				; dword boundary lWidth=(((width-1)/4)+1)*4 	

;;; ----------------------------------------------------------
;;; bmp buffer starts here
;;; ----------------------------------------------------------
bmpBuf	equ	$
type	resw	1		; header
size	resd	1
resvd1	resw	1
resvd2	resw	1
offset	resd	1
;;;
size2	resd	1		; information header
width	resd	1
height	resd	1
planes	resw	1
xbits	resw	1
compr	resd	1
imgsize	resd	1
xres	resd	1
yres	resd	1
nocol	resd	1
impcol	resd	1
headLen equ	$-bmpBuf	; length of header
	
pixelBuf resb	MAXPIXEL*3	; times 3 bytes (RGB)

	
;;; ---------------------------------------------------------
;;; code area
;;; ---------------------------------------------------------
	section	.text
	global	_start

_start:
;;; --- check that user entered more than 1 argument on command line ---
	pop	ebx		; get # of arguments on command line
	cmp	ebx,1
	jg	process		; if user forgot file name, exit
	dumpStr "Syntax: progName filename"
	jmp	exit

;;; --- get filename from command line ---
process:	
	pop	ebx		; pointer to argv[0] (name of program)
	pop	ebx		; pointer to argv[1]
	mov	edi,filename	; pointer to filename
copy:	mov	al,[ebx]	; copy name of file from argv[1] to
	mov	[edi],al	; filename string, until \0 is copied
	inc	ebx
	inc	edi
	cmp	al,0
	jne	copy
	
;;; --- open file ---
        openFile filename, [handle], errorMsg, errorLen
        

;;; --- read file in buffer ---
        readFile [handle], bmpBuf, MAXPIXEL, noRead
        
;;; --- compute length of a line of pixel:
;;; line length = (( byte width+3)/4)*4 where
;;; byte width = 3 * width, since we have 3 bytes per pixel
;;; 
	mov	eax,[width]
	add	eax,[width]
	add	eax,[width]	; eax <-- 3 x width
	dec	eax		; eax
	shr	eax,2		; 
	inc	eax
	shl	eax,2
	mov	[lWidth],eax

;;; --------------------------------------------------------------
;;; Find the address of the first byte of the image and put
;;; it in ebx
;;; --------------------------------------------------------------

  	mov	eax,0
        push eax
        push eax
        call  hw2index

 
	;; -----------------------------------
	;; add your byte-examining loop  here!
        ;you can access the bytes of the pixels as  byte[ebx+pixelBuf]
	;; -----------------------------------


	;; -----------------------------------
	;; end of pixel loop area
	;; -----------------------------------
		
;;; --- position file pointer back to beginning of file ---
 	seek0	[handle]
	
;;; --- write contents back to file ---
 	writeBuf [handle], bmpBuf, noRead
	
;;; --- close file ---
	close	[handle]
	
;;; --- exit() ---
exit:	
	mov	eax,SYS_EXIT
	mov	ebx,0
	int	0x80		; final system call


	
;;; -------------------------------------------------------------
;;; hw2index:	converts height and width to pixel index
;;;             index returned in ebx.  Note that computation is
;;;             performed with lWidth which must be computed
;;;             separately and is the number of bytes in one line
;;;             of pixel, such that number of byte is a multiple of
;;;             4.
;;; registers modified:	 ebx
;;; -------------------------------------------------------------
hw2index:
	push	ebp
	mov	ebp,esp
	
	push	eax		; save eax and edx
	push	edx
	mov	eax,[lWidth]	
	xor	edx,edx
	mul	dword[ebp+12]	; eax = lWidth * h
	add	eax,[ebp+8]	; eax += 3*w
	add	eax,[ebp+8]
	add	eax,[ebp+8]
	mov	ebx,eax		; pass result in ebx
	
	pop	edx
	pop	eax
	pop	ebp
	
	ret	8