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191 lines
3.6 KiB
NASM
191 lines
3.6 KiB
NASM
[org 0x1000]
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push 0a000h ;Video memory graphics segment
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pop es
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mov ax, 0012h ;320x200@8bpp
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int 10h
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push 0Eh ;Blue
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push 10 ;cX
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push 10 ;cY
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push 10 ;Radius
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call drawFilledCircle
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push 02h ;Blue
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push 40 ;cX
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push 40 ;cY
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push 30 ;Radius
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call drawFilledCircle
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push 06h ;Blue
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push 140 ;cX
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push 100 ;cY
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push 70 ;Radius
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call drawFilledCircle
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main: ; Label for the start of the main program
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mov ax,0x0000 ; Setup the Data Segment register
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; Location of data is DS:Offset
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mov ds,ax ; This can not be loaded directly it has to be in two steps.
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; 'mov ds, 0x0000' will NOT work due to limitations on the CPU
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mov si, HelloWorld ; Load the string into position for the procedure.
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call PutStr ; Call/start the procedure
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mov dx, 0C14h ;DH=12 row, DL=20 column
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mov bh, 0 ;BH=0 display page
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mov ah, 02h ;AH=02h set cursor position function
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int 10h ;video BIOS interrupt
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mov bx, 000Ch ;BH=0 display page, BL=12 red
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mov ax, 0E42h ;AH=0Eh teletype function, AL=66 capital B
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int 10h ;video BIOS interrupt
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; Procedures
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PutStr: ; Procedure label/start
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; Set up the registers for the interrupt call
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mov ah,0x0E ; The function to display a chacter (teletype)
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mov bh,0x00 ; Page number
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mov bl,0x0C ; Normal text attribute
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.nextchar ; Internal label (needed to loop round for the next character)
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lodsb ; I think of this as LOaD String Block
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; (Not sure if thats the real meaning though)
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; Loads [SI] into AL and increases SI by one
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; Check for end of string '0'
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or al,al ; Sets the zero flag if al = 0
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; (OR outputs 0's where there is a zero bit in the register)
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jz .return ; If the zero flag has been set go to the end of the procedure.
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; Zero flag gets set when an instruction returns 0 as the answer.
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int 0x10 ; Run the BIOS video interrupt
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jmp .nextchar ; Loop back round tothe top
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.return ; Label at the end to jump to when complete
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ret ; Return to main program
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;Color
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;cX
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;cY
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;R
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drawFilledCircle:
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push bp
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mov bp, sp
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sub sp, 02h
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mov cx, WORD [bp+04h] ;R
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mov ax, cx
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mul ax ;AX = R^2
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mov WORD [bp-02h], ax ;[bp-02h] = R^2
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mov ax, WORD [bp+06h]
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sub ax, cx ;i = cY-R
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mov bx, WORD [bp+08h]
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sub bx, cx ;j = cX-R
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shl cx, 1
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mov dx, cx ;DX = Copy of 2R
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.advance_v:
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push cx
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push bx
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mov cx, dx
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.advance_h:
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;Save values
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push bx
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push ax
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push dx
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;Compute (i-y) and (j-x)
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sub ax, WORD [bp+06h]
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sub bx, WORD [bp+08h]
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mul ax ;Compute (i-y)^2
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push ax
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mov ax, bx
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mul ax
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pop bx ;Compute (j-x)^2 in ax, (i-y)^2 is in bx now
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add ax, bx ;(j-x)^2 + (i-y)^2
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cmp ax, WORD [bp-02h] ;;(j-x)^2 + (i-y)^2 <= R^2
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;Restore values before jump
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pop dx
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pop ax
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pop bx
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ja .continue ;Skip pixel if (j-x)^2 + (i-y)^2 > R^2
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;Write pixel
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push WORD [bp+0ah]
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push bx
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push ax
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call writePx
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.continue:
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;Advance j
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inc bx
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loop .advance_h
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;Advance i
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inc ax
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pop bx ;Restore j
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pop cx ;Restore counter
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loop .advance_v
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add sp, 02h
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pop bp
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ret 08h
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;Color
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;X
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;Y
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writePx:
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push bp
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mov bp, sp
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push ax
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push bx
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mov bx, WORD [bp+04h]
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mov ax, bx
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shl bx, 6
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shl ax, 8
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add bx, ax ;320 = 256 + 64
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add bx, WORD [bp+06h]
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mov ax, WORD [bp+08h]
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;TODO: Clip
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mov BYTE [es:bx], al
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pop bx
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pop ax
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pop bp
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ret 06h
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HelloWorld db ' Not My Default Bootloader',0x0D,0x0A,0
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