81 lines
1.6 KiB
NASM
81 lines
1.6 KiB
NASM
; Program to illustrate operation of Map Mask register when drawing
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; to memory that already contains data.
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; By Michael Abrash.
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;
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stack segment para stack ‘STACK'
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db 512 dup(?)
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stack ends
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;
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EGA_VIDEO_SEGMENT equ 0a000h ;EGA display memory segment
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;
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; EGA register equates.
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;
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SC_INDEX equ 3c4h ;SC index register
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SC_MAP_MASK equ 2 ;SC map mask register
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;
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; Macro to set indexed register INDEX of SC chip to SETTING.
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;
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SETSC macro INDEX, SETTING
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mov dx,SC_INDEX
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mov al,INDEX
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out dx,al
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inc dx
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mov al,SETTING
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out dx,al
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dec dx
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endm
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;
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cseg segment para public ‘CODE#146;
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assume cs:cseg
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start proc near
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;
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; Select 640x480 graphics mode.
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;
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mov ax,012h
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int 10h
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;
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mov ax,EGA_VIDEO_SEGMENT
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mov es,ax ;point to video memory
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;
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; Draw 24 10-scan-line high horizontal bars in green, 10 scan lines apart.
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;
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SETSC SC_MAP_MASK,02h ;map mask setting enables only
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; plane 1, the green plane
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sub di,di ;start at beginning of video memory
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mov al,0ffh
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mov bp,24 ;# bars to draw
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HorzBarLoop:
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mov cx,80*10 ;# bytes per horizontal bar
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rep stosb ;draw bar
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add di,80*10 ;point to start of next bar
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dec bp
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jnz HorzBarLoop
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;
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; Fill screen with blue, using Map Mask register to enable writes
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; to blue plane only.
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;
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SETSC SC_MAP_MASK,01h ;map mask setting enables only
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; plane 0, the blue plane
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sub di,di
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mov cx,80*480 ;# bytes per screen
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mov al,0ffh
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rep stosb ;perform fill (affects only
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; plane 0, the blue plane)
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;
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; Wait for a keystroke.
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;
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mov ah,1
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int 21h
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;
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; Restore text mode.
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;
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mov ax,03h
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int 10h
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;
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; Exit to DOS.
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;
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mov ah,4ch
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int 21h
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start endp
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cseg ends
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end start
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