; DISPLAY.ASM - contains a collection of video-related procedures and ; functions for use with Microsoft high-level languages. ; ; Author: Christy Gemmell ; For: Assembly-Language Toolbox for QuickBASIC ; Version: 4.06 ; Date: 22/9/1990 ; ; Compatible with the QuickBASIC 4.0, 4.5 and BASIC 6 compilers ; Assembled using Microsoft Macro Assembler, MASM version 5.1 ; ; Global symbols and procedures. ; .model medium public ScreenAddress, ScreenWrite public VideoType, FastPrint .code ; Data Division. ; ; Video parameters - default to monochrome screen display ; SnowFlag db 0 ; Snow prevention flag VideoRam dw 0B000h ; Current video segment VideoPort dw 03BAh ; Current video status port Param1 label word Mode db 7 ; Current screen mode Columns db 80 ; Current screen width Param2 label word Rows db 25 ; Current screen length ActivePage db 0 ; Current video page ;Listing 1.1 Collect video information ; Collect information about the current video display. ; ; Returns: AL = Current display mode ; AH = Screen width in columns ; BL = Screen height in rows ; BH = Active display page ; ; The correct video display segment and CRT status port addresses are ; determined for the current system and, if necessary, the internal ; 'snow' prevention flag is set. ; VideoType proc far push cx ; Preserve these push dx ; registers push es ; push bp ;Added this [DEC] mov ah,0Fh ; ROM-BIOS Service 16 int 10h ; - Check video mode cmp al,7 ; Monochrome display? je Type_02 ; Yes, use defaults mov cs:VideoRam,0B800h ; Otherwise set up mov cs:VideoPort,03DAh ; for colour Type_01: mov cs:Param1,ax ; Save display mode ; and width push bx ; Save active display xor bh,bh ; page mov dl,24 ; Default to 25 rows mov ax,1130h ; ROM-BIOS Service 16 int 10h ; - get font pop bx ; information mov bl,dl ; DL = rows - 1 inc bl ; Save video page mov cs:Param2,bx ; and height mov bl,10h ; Test for presence mov ah,12h ; of an EGA or VGA int 10h ; display adaptor cmp bl,10h ; Any response? jne Type_02 ; Yes, can't be a CGA mov cs:SnowFlag,1 ; Set snow prevention Type_02: ; flag mov bx,cs:Param2 ; Recover page and ; screen height mov ax,cs:Param1 ; Recover screen mode ; and width pop bp ;added [DEC] pop es ; Clean up the stack pop dx pop cx ret ; Return to caller VideoType endp ;Listing 1.2 Convert row/column co-ordinates to an address ; Calculate address from a pair of row/column co-ordinates. ; ; Given the row/column column co-ordinate of a character on the ; screen, this function returns the segment:offset address of that ; character in video memory. The address is correctly adjusted to ; the start of the the currently active display page, but no check ; is made to ensure that the co-ordinates supplied are within the ; actual screen bounds. ; ; Input: AL = Row co-ordinate of character (base zero). ; AH = Column co-ordinate of character (base zero). ; Output: ES:DI==> Address in video display buffer of the ; character cell specified. ; DX = CRT status register port address. ; ; It is assumed that a previous call has been made to the VideoType ; function to determine the screen width, the port address of the ; CRT status register and the correct video display segment. ; ScreenAddress proc far push ax ; Save working registers push bx mov bh,ah ; Column to BH mov bl,cs:Columns ; Get current screen width shl bl,1 ; Add in attribute bytes mul bl ; Multiply by row number xor bl,bl ; Calculate xchg bh,bl ; column offset shl bl,1 ; in BX add ax,bx ; Add it to the row offset mov di,ax ; and copy to DI xor ax,ax ; Index to ROM-BIOS mov es,ax ; data in low memory mov ax,es:[44Eh] ; Get offset of current page add di,ax ; Adjust target pointer mov es,cs:VideoRam ; Return segment of video RAM mov dx,cs:VideoPort ; Return CRT status port pop bx ; Clean up the stack pop ax ret ; and return to caller ScreenAddress endp ;Listing 1.3 Output a character and attribute to the screen. ; ; Output a character and attribute to the video display. ; ; If the 'snow prevention' flag is set, this routine waits until the ; beginning of the next CRT horizontal retrace period before writing ; data to the display. This is necessary only on computers fitted ; with Colour Graphics Adaptor (CGA) which may suffer from glitches ; or screen snow if data is written to the screen while the video ; buffer is being refreshed. ; ; Input: ES:DI==> Address in the video display buffer where ; the data is to be written. ; DX = Port address of CRT status register. ; AL = Character to output. ; AH = Display attribute of character. ; ; Output: DI Updated to point to next output address. ; ScreenWrite proc far push bx ; Preserve BX cmp cs:SnowFlag,0 ; Snow prevention needed? cli ; Don't interrupt! jz Write_3 ; No, don't bother mov bx,ax ; Save byte and attribute Write_1: in al,dx ; Read video port test al,1 ; Test bit zero jnz Write_1 ; Wait until it's reset Write_2: in al,dx ; Read port again test al,1 ; Test bit zero jz Write_2 ; Wait until it's set mov ax,bx ; Recover data Write_3: stosw ; Write data to screen sti ; Restore interrupts pop bx ; Restore BX ret ScreenWrite endp ;Listing 1.4 Main program module. ; Fast screen printing. ; ; This procedure outputs text directly to the video display without ; going through DOS or ROM-BIOS services. ; FastPrint proc far push bp ; Save Base pointer mov bp,sp ; Establish stack frame push es ; Save Extra Segment push si ; and index pointers push di call VideoType ; Get video parameters mov dh,ah ; Load screen dimensions mov dl,bl ; into DX mov ax,[bp+12] ; Get row number dec al ; Convert to base zero cmp al,0 ; Top screen row? jae Fast_01 ; Jump if not below xor al,al ; Don't go over the top! Fast_01: cmp al,dl ; Bottom row? jb Fast_02 ; Go no further mov al,dl dec al Fast_02: mov bx,[bp+10] ; Get column number mov ah,bl ; into AH dec ah ; Convert to base zero cmp ah,0 ; Leftmost column? jae Fast_03 ; Jump if not below xor ah,ah ; Don't go off the screen Fast_03: cmp ah,dh ; Rightmost column? jb Fast_04 ; Go no further mov ah,dh ; Don't go off the screen dec ah ; Base zero, remember? Fast_04: call ScreenAddress ; Calculate target address mov bx,[bp+8] ; Index to string descriptor mov cx,[bx] ; Get string length cmp cx,0 ; Make sure it isn't ja Fast_05 ; a null string mov ax,1 ; If so set Error code jmp short Fast_07 ; and abort Fast_05: mov si,[bx+2] ; DS:SI==> string data mov ax,[bp+6] ; Get display attribute xchg ah,al ; into AH cld ; Clear direction flag Fast_06: lodsb ; Get a byte from the string call ScreenWrite ; Write byte and attribute loop Fast_06 ; For length of string xor ax,ax ; Report success Fast_07: pop di ; Clean up the stack pop si pop es pop bp ret 8 ; Return to QuickBASIC FastPrint endp end