Assembly two-dimensional array of pixels - arrays

Question

How could I do something like this in assembly? DOS 16bit graphic mode
int start_x=1, start_y=1;
for(int i=0; i<8; i++){
for(int j=0; j<8; j++){
if(T34[i][j]==1) put_colour_pixel(start_x+i, start_y+j);
else put_black_pixel(start_x+i, start_y+j);
}
}
:edit:
So my loops pretty work. How to connect it to table with 0 and 1.
mov ax, 10 ; Y start line
mov bx, 20 ; X start line
mov dl, 4 ; colour (red)
mov cx, 5 ; loop top counter
top:
add ax, 1
push cx ;loop top counter
mov cx, 10
inside:
add bx, 1
push ax
push bx
push cx
call putpixel
pop cx
pop bx
pop ax
loop inside
mov bx, 20 ;next line X go to start X
pop cx ;loop top counter
loop top
/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////////////////
My new code:
segment .data
segment .code
..start:
mov ax, 13h
int 10h ; switch to 320x200 mode
mov ax, 0a000h ; The offset to video memory
mov es, ax ; We load it to ES through AX,
; because immediate operation
; is not allowed on ES
;;;;;;;;;;;;;;;;;;;;;;
mov di, T34
mov si, 8
;------------------------------------
P1: mov bp, 8
;----------------
P2: cmp BYTE[di], 1
jnz short NOHIT
NOHIT: ; increase the x position
push ax
push bx
push cx
mov ax,si ;Y
mov bx,bp ;X
mov dl, 1 ; here I should take '0' or '1' from table
call putpixel
pop cx
pop bx
pop ax
inc di ; increase offset address of array
dec bp
jnz P2
;-------------
; increase the y position + substract 8 from x position
dec si
jnz P1
;------------------------------------
;;;;;;;;;;;;;;;;;;;;;;;;;
xor ah, ah
int 16h ; keyboard (wait for key)
mov ax, 3
int 10h ; go to text mode
mov ax, 4c00h
int 21h ; return to DOS, exit code 0
;;;;;;;;;;;;;;;;;;;;;
putpixel:
push dx ; mul changes dx too
mov cx, 320
mul cx ; multiply Y (ax) by 320 (one row)
add ax, bx ; and add X (bx) (result= dx:ax)
mov di, ax
pop dx
mov [es:di], dl ; store color/pixel
ret
;;;;;;;;;;;;;;;;;;;;;;
T34 DB 1,1,1,1,1,1,1,1
DB 1,0,0,0,0,0,0,0
DB 1,0,0,0,0,0,0,0
DB 1,0,0,0,0,0,0,0
DB 1,1,1,1,1,1,1,1
DB 1,0,0,0,0,0,0,0
DB 1,0,0,0,0,0,0,0
DB 1,1,1,1,1,1,1,1
I have changed order and now it is drawing square in left corner (as I expected). Did I change order rigth?
I suppose that letter will be spinned, but it is not problem for me. I can fix it later.
Now I should go to '0' or '1' in table and set color. Which register have "0" or "1"?
So mostly I have problem with colour.
I have try this, but I have error. I have try set colour black (0) or blue (1)
push dx
mov ax, bp ; X*8
mov cx,8
mul cx
add ax, si ; X*8 +Y
add ax, di ; tab0 + X*8+Y
mov dl, ax; here is error, here I set the colour
pop dx
So I don't know how to fix it :( I have try different possibilities and northing work.

Answer 1

mov di, T34
mov si, 8
;------------------------------------
P1: mov bp, 8
;----------------
P2: cmp BYTE[di], 1
jnz short NOHIT
; save used REGISTER
; load register with the X,Y position and color
call putpixel
; get back the saved Register
NOHIT: ; increase the x position
inc di ; increase offset address of array
dec bp ; decrease counter and set zeroflag if register is zero
jnz P2 ; jump if zeroflag is not set
;-------------
; increase the y position + substract 8 from x position
dec si
jnz P1
;------------------------------------
It is also possible to start the counters for the loops with 0 for to increase the counter, but then we need a compare instruction for to leave the loop, if we want to run the loop from 0 to 8. The offset addresses inside of the array are pointed independent with no relationship to the counters.
With a little modifying (put an additional jump instruction in the code and a second call) it is also possible to set a black pixel if the byte of the array is 0. But i think this simple form of a nested loop is easier to understand in the first time.
Edit: Now it is compatible for NASM.
Edit2: Maybe it is more simple to store the x,y coordinates into a known ram location for modifying and reloading inside of a loop, if many parameters are in use.
Our ram location:
Color DB ? ; define byte
X_Pos DW ? ; define word
Y_Pos DW ?
Examples for to show how to access a memory location (default segment is DS):
mov [X_Pos], ax
mov [X_Pos], bx
mov [Color], dl
mov ax, [X_Pos]
mov bx, [Y_Pos]
mov dl, [Color]
mov WORD[X_Pos], 10
inc WORD[X_Pos]
sub WORD[X_Pos], 8
mov BYTE[Color], 4
inc BYTE[Color]
Edit3:
mov dl, ax; here is error, here I set the colour
It is not possible to mix an 8 bit register with a 16 Bit register.
Note:
AX = AL+AH
DX = DL+DH
Existing instruction are:
mov dl, al
mov dl, ah
mov dx, ax
movzx dl, ax