Text mode 80x25 16-bit

[maxrio]

Hi! im trying to make a procedure wich saves what is on screen in a variable defined on the data segment (antes dw 2000 dup (?)). It compiles well but it freezes the program when it is called by it(program). BTW: this program is in textmode 80x25 16-bit and i am not allowed to use BIOS or DOS interruptions:

;Saves the screen image insede a rectangle
;in variable antes on the data segment.
;gets the upper left corner of the rectangle from bx
;gets the lower right corner of the rectangle from ax
;the rectangle's width in cx

        ;|------cx---------|
        ;
        ;
        ;bx-----------------
        ;|                 |
        ;|                 |
        ;------------------ax
	guarda	PROC	NEAR
			push	ax
			push	bx
			push	cx
			push	dx
			push	si
			xor		si, si
	c2:		push            cx
			push	        bx
			mov	dx, word ptr es:[bx]
			mov		antes[si], dx
			inc		si
			add		bx, 2
			loop	        c2
                        pop             cx
			cmp		ax, bx
			je		fgurda
			pop		bx
			add		bx, 160
			jmp		c2
	fgurda:         pop		bx
			pop		si
			pop		dx
			pop		cx
			pop		bx
			pop		ax
			ret
	guarda	EndP

Any ideas of what is wrong?

[Ancient Dragon]

what's the value of es when that function is entered? The screen address is at 0xB800:0000, so you have to read starting from there. I think your function needs to set the value of es and not assume it already contains the correct segment value.

bx = upper left corner
ax = lower right corner
cx = width -- this is one problem. We need the height, not the width. The width can be calculated from bx and ax.

[maxrio]

what's the value of es when that function is entered? The screen address is at 0xB800:0000, so you have to read starting from there. I think your function needs to set the value of es and not assume it already contains the correct segment value.

bx = upper left corner
ax = lower right corner
cx = width -- this is one problem. We need the height, not the width. The width can be calculated from bx and ax.

Well, this is a procedure, that means that everything is already set up(i.e es points to b800h), i display all menus and interface but i need this procedure to display a drop down submenu.I think we have a semantic problem cuz i find easier to use width instead of height. Without this procedure the drop down submenu displays well, but i lose the image that was where the submenu is now.

[Ancient Dragon]

you need both width and height so that your program knows how many lines of text to save. They can both be calculated when you know the upper-left and lower-right coordinates. It might be easier to just save the contents of the entire screen, write sub-menu, then restore the screen to erase the sub-menu. If you don't do anything with the color attributes than all you need is a buffer that's 24*80 = 1920 bytes. double that if you need the color attributes too.

[maxrio]

thanks for your help, after some rest i re-checked my code and found a few problems regarding the stack. I wasn't handling well the stack so that caused an infinite loop wich obviously filled the stack. If you check my previous code you'll find that i made a loop that pushed the cx every call and that wasn't good for the pop instruction. Here's a perfectly working code:

;Saves the screen image insede a rectangle
;in variable antes on the data segment.
;gets the upper left corner of the rectangle from bx
;gets the lower right corner of the rectangle from ax
;the rectangle's width in cx         
;|------cx---------|        
;        
;        
;bx-----------------        
;|                 |        
;|                 |        
;------------------ax

guarda	PROC	NEAR
			push	         ax
			push	         bx
			push	         cx
			push	         dx
			push	         si
			xor		si, si
			dec		cx
	c2:		push	         cx
			push	         bx
	c_1:	         mov		dx, word ptr es:[bx]
			mov		antes[si], dx
			inc		si
			add		bx, 2
			loop	         c_1
			cmp		ax, bx
			je		fgurda
			pop		bx
			add		bx, 160
			pop		cx
			jmp		c2
	fgurda:           pop		bx
			pop		cx
			pop		si
			pop		dx
			pop		cx
			pop		bx
			pop		ax
			ret
	guarda	EndP

[maxrio]

just a small correction, double post since i cant edit, in line 26 the code should go: add si, 2 and in line 30: jl fgurda. That's all :)