Programmer 7500/MAX_PROGRAMMERS.iso/INFO/PROGJRN/PJ_VGA.ARC/VGA71-L2.ASM

Assembly Source File | 1988-10-16 | 6.8 KB | 264 lines

;
; *** Listing 2 ***
;
; Program to demonstrate the two pages available in 320x400
; 256-color modes on a VGA.  Draws diagonal color bars in all
; 256 colors in page 0, then does the same in page 1 (but with
; the bars tilted the other way), and finally draws vertical
; color bars in page 0.
;
VGA_SEGMENT    equ    0a000h
SC_INDEX    equ    3c4h    ;Sequence Controller Index register
GC_INDEX    equ    3ceh    ;Graphics Controller Index register
CRTC_INDEX    equ    3d4h    ;CRT Controller Index register
MAP_MASK    equ    2    ;Map Mask register index in SC
MEMORY_MODE    equ    4    ;Memory Mode register index in SC
MAX_SCAN_LINE    equ    9    ;Maximum Scan Line reg index in CRTC
START_ADDRESS_HIGH equ    0ch    ;Start Address High reg index in CRTC
UNDERLINE    equ    14h    ;Underline Location reg index in CRTC
MODE_CONTROL    equ    17h    ;Mode Control register index in CRTC
GRAPHICS_MODE    equ    5    ;Graphics Mode register index in GC
MISCELLANEOUS    equ    6    ;Miscellaneous register index in GC
SCREEN_WIDTH    equ    320    ;# of pixels across screen
SCREEN_HEIGHT    equ    400    ;# of scan lines on screen
WORD_OUTS_OK    equ    1    ;set to 0 to assemble for
                ; computers that can't handle
                ; word outs to indexed VGA registers
;
stack    segment para stack 'STACK'
    db    512 dup (?)
stack    ends
;
; Macro to output a word value to a port.
;
OUT_WORD    macro
if WORD_OUTS_OK
    out    dx,ax
else
    out    dx,al
    inc    dx
    xchg    ah,al
    out    dx,al
    dec    dx
    xchg    ah,al
endif
    endm
;
; Macro to output a constant value to an indexed VGA register.
;
CONSTANT_TO_INDEXED_REGISTER    macro    ADDRESS, INDEX, VALUE
    mov    dx,ADDRESS
    mov    ax,(VALUE shl 8) + INDEX
    OUT_WORD
    endm
;
Code    segment
    assume    cs:Code
Start    proc    near
;
; Set 320x400 256-color mode.
;
    call    Set320By400Mode
;
; We're in 320x400 256-color mode, with page 0 displayed.
; Let's fill page 0 with color bars slanting down and to the right.
;
    sub    di,di        ;page 0 starts at address 0
    mov    bl,1        ;make color bars slant down and
                ; to the right
    call    ColorBarsUp    ;draw the color bars
;
; Now do the same for page 1, but with the color bars
; tilting the other way.
;
    mov    di,8000h    ;page 1 starts at address 8000h
    mov    bl,-1        ;make color bars slant down and
                ; to the left
    call    ColorBarsUp    ;draw the color bars
;
; Wait for a key and flip to page 1 when one is pressed.
;
    call    GetNextKey
    CONSTANT_TO_INDEXED_REGISTER CRTC_INDEX,START_ADDRESS_HIGH,80h
                ;set the Start Address High register
                ; to 80h, for a start address of 8000h
;
; Draw vertical bars in page 0 while page 1 is displayed.
;
    sub    di,di        ;page 0 starts at address 0
    sub    bl,bl        ;make color bars vertical
    call    ColorBarsUp    ;draw the color bars
;
; Wait for another key and flip back to page 0 when one is pressed.
;
    call    GetNextKey
    CONSTANT_TO_INDEXED_REGISTER CRTC_INDEX,START_ADDRESS_HIGH,00h
                ;set the Start Address High register
                ; to 00h, for a start address of 0000h
;
; Wait for yet another key and return to text mode and end when
; one is pressed.
;
    call    GetNextKey
    mov    ax,0003h
    int    10h    ;text mode
    mov    ah,4ch
    int    21h    ;done
;
Start    endp
;
; Sets up 320x400 256-color modes.
;
; Input: none
;
; Output: none
;
Set320By400Mode    proc    near
;
; First, go to normal 320x200 256-color mode, which is really a
; 320x400 256-color mode with each line scanned twice.
;
    mov    ax,0013h  ;AH = 0 means mode set, AL = 13h selects
            ; 256-color graphics mode
    int    10h    ;BIOS video interrupt
;
; Change CPU addressing of video memory to linear (not odd/even,
; chain, or chain 4), to allow us to access all 256K of display
; memory. When this is done, VGA memory will look just like memory
; in modes 10h and 12h, except that each byte of display memory will
; control one 256-color pixel, with 4 adjacent pixels at any given
; address, one pixel per plane.
;
    mov    dx,SC_INDEX
    mov    al,MEMORY_MODE
    out    dx,al
    inc    dx
    in    al,dx
    and    al,not 08h    ;turn off chain 4
    or    al,04h        ;turn off odd/even
    out    dx,al
    mov    dx,GC_INDEX
    mov    al,GRAPHICS_MODE
    out    dx,al
    inc    dx
    in    al,dx
    and    al,not 10h    ;turn off odd/even
    out    dx,al
    dec    dx
    mov    al,MISCELLANEOUS
    out    dx,al
    inc    dx
    in    al,dx
    and    al,not 02h    ;turn off chain
    out    dx,al
;
; Now clear the whole screen, since the mode 13h mode set only
; cleared 64K out of the 256K of display memory. Do this before
; we switch the CRTC out of mode 13h, so we don't see garbage
; on the screen when we make the switch.
;
    CONSTANT_TO_INDEXED_REGISTER SC_INDEX,MAP_MASK,0fh
                ;enable writes to all planes, so
                ; we can clear 4 pixels at a time
    mov    ax,VGA_SEGMENT
    mov    es,ax
    sub    di,di
    mov    ax,di
    mov    cx,8000h    ;# of words in 64K
    cld
    rep    stosw        ;clear all of display memory
;
; Tweak the mode to 320x400 256-color mode by not scanning each
; line twice.
;
    mov    dx,CRTC_INDEX
    mov    al,MAX_SCAN_LINE
    out    dx,al
    inc    dx
    in    al,dx
    and    al,not 1fh    ;set maximum scan line = 0
    out    dx,al
    dec    dx
;
; Change CRTC scanning from doubleword mode to byte mode, allowing
; the CRTC to scan more than 64K of video data.
;
    mov    al,UNDERLINE
    out    dx,al
    inc    dx
    in    al,dx
    and    al,not 40h    ;turn off doubleword
    out    dx,al
    dec    dx
    mov    al,MODE_CONTROL
    out    dx,al
    inc    dx
    in    al,dx
    or    al,40h    ;turn on the byte mode bit, so memory is
            ; scanned for video data in a purely
            ; linear way, just as in modes 10h and 12h
    out    dx,al
    ret
Set320By400Mode    endp
;
; Draws a full screen of slanting color bars in the specified page.
;
; Input:
;    DI = page start address
;    DL = 1 to make the bars slant down and to the right, -1 to
;        make them slant down and to the left, 0 to make
;        them vertical.
;
ColorBarsUp    proc    near
    mov    ax,VGA_SEGMENT
    mov    es,ax    ;point to display memory
    sub    bh,bh    ;start with color 0
    mov    si,SCREEN_HEIGHT ;# of rows to do
    mov    dx,SC_INDEX
    mov    al,MAP_MASK
    out    dx,al    ;point the SC Index reg to the Map Mask reg
    inc    dx    ;point DX to the SC Data register
RowLoop:
    mov    cx,SCREEN_WIDTH/4
            ;there are 4 pixels at each address, so
            ; each 320-pixel row is 80 bytes wide
            ; in each plane
    push    bx    ;save the row-start color
ColumnLoop:
MAP_SELECT = 1
    rept    4    ;do all 4 pixels at this address with
            ; in-line code
    mov    al,MAP_SELECT
    out    dx,al    ;select planes 0, 1, 2, and 3 in turn
    mov    es:[di],bh ;write this plane's pixel
    inc    bh    ;set the color for the next pixel
MAP_SELECT = MAP_SELECT shl 1
    endm
    inc    di    ;point to the address containing the next
            ; 4 pixels
    loop    ColumnLoop ;do any remaining pixels on this line
    pop    bx    ;get back the row-start color
    add    bh,bl    ;select next row-start color (controls
            ; slanting of color bars)
    dec    si    ;count down lines on the screen
    jnz    RowLoop
    ret
ColorBarsUp    endp
;
; Waits for the next key and returns it in AX.
;
GetNextKey    proc    near
WaitKey:
    mov    ah,1
    int    16h
    jz    WaitKey    ;wait for a key to become available
    sub    ah,ah
    int    16h    ;read the key
    ret
GetNextKey    endp
;
Code    ends
;
    end    Start