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XMAIN.ASM
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Assembly Source File
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1993-04-05
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34KB
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1,091 lines
;-----------------------------------------------------------------------
; MODULE XMAIN
;
; Initialization, panning and split screen functions for all MODE X 256
; Color resolutions
;
; Compile with Tasm.
; C callable.
;
;
; ****** XLIB - Mode X graphics library ****************
; ****** ****************
; ****** Written By Themie Gouthas ****************
; ****** Aeronautical Research Laboratory ****************
; ****** Defence Science and Technology Organisation ****************
; ****** Australia ****************
;
; egg@dstos3.dsto.gov.au
; teg@bart.dsto.gov.au
;
; MODIFICATIONS:
; 26-9-92: Pel panning code added
;-----------------------------------------------------------------------
include xlib.inc
include xmain.inc
.data
; Mode X CRTC register tweaks for various resolutions
X320Y200 label word
db 0e3h ; dot clock
db 02 ; Number of CRTC Registers to update
dw 00014h ; turn off dword mode
dw 0e317h ; turn on byte mode
dw 320 ; width
dw 200 ; height
X320Y240 label word
db 0e3h ; dot clock
db 10 ; Number of CRTC Registers to update
dw 00d06h ; vertical total
dw 03e07h ; overflow (bit 8 of vertical counts)
dw 04109h ; cell height (2 to double-scan)
dw 0ea10h ; v sync start
dw 0ac11h ; v sync end and protect cr0-cr7
dw 0df12h ; vertical displayed
dw 00014h ; turn off dword mode
dw 0e715h ; v blank start
dw 00616h ; v blank end
dw 0e317h ; turn on byte mode
dw 320 ; width
dw 240 ; height
X360Y200 label word
db 0e7h ; dot clock
db 08 ; Number of CRTC Registers to update
dw 06b00h ; horz total
dw 05901h ; horz displayed
dw 05a02h ; start horz blanking
dw 08e03h ; end horz blanking
dw 05e04h ; start h sync
dw 08a05h ; end h sync
dw 00014h ; turn off dword mode
dw 0e317h ; turn on byte mode
dw 360 ; width
dw 200 ; height
X360Y240 label word
db 0e7h ; dot clock
db 17 ; Number of CRTC Registers to update
dw 06b00h ; horz total
dw 05901h ; horz displayed
dw 05a02h ; start horz blanking
dw 08e03h ; end horz blanking
dw 05e04h ; start h sync
dw 08a05h ; end h sync
dw 00d06h ; vertical total
dw 03e07h ; overflow (bit 8 of vertical counts)
dw 04109h ; cell height (2 to double-scan)
dw 0ea10h ; v sync start
dw 0ac11h ; v sync end and protect cr0-cr7
dw 0df12h ; vertical displayed
dw 02d13h ; offset;
dw 00014h ; turn off dword mode
dw 0e715h ; v blank start
dw 00616h ; v blank end
dw 0e317h ; turn on byte mode
dw 360
dw 240
X320Y400 label word
db 0e3h ; dot clock
db 03 ; Number of CRTC Registers to update
dw 04009h ; cell height
dw 00014h ; turn off dword mode
dw 0e317h ; turn on byte mode
dw 320 ; width
dw 400 ; height
X320Y480 label word
db 0e3h ; dotclock
db 10 ; Number of CRTC Registers to update
dw 00d06h ; vertical total
dw 03e07h ; overflow (bit 8 of vertical counts)
dw 04009h ; cell height (2 to double-scan)
dw 0ea10h ; v sync start
dw 0ac11h ; v sync end and protect cr0-cr7
dw 0df12h ; vertical displayed
dw 00014h ; turn off dword mode
dw 0e715h ; v blank start
dw 00616h ; v blank end
dw 0e317h ; turn on byte mode
dw 320 ; width
dw 480 ; height
X360Y400 label word
db 0e7h ; dot clock
db 09 ; Number of CRTC Registers to update
dw 06b00h ; horz total
dw 05901h ; horz displayed
dw 05a02h ; start horz blanking
dw 08e03h ; end horz blanking
dw 05e04h ; start h sync
dw 08a05h ; end h sync
dw 04009h ; cell height
dw 00014h ; turn off dword mode
dw 0e317h ; turn on byte mode
dw 360 ; width
dw 400 ; height
X360Y480 label word
db 0e7h
db 17
dw 06b00h ; horz total
dw 05901h ; horz displayed
dw 05a02h ; start horz blanking
dw 08e03h ; end horz blanking
dw 05e04h ; start h sync
dw 08a05h ; end h sync
dw 00d06h ; vertical total
dw 03e07h ; overflow
dw 04009h ; cell height
dw 0ea10h ; v sync start
dw 0ac11h ; v sync end and protect cr0-cr7
dw 0df12h ; vertical displayed
dw 02d13h ; offset
dw 00014h ; turn off dword mode
dw 0e715h ; v blank start
dw 00616h ; v blank end
dw 0e317h ; turn on byte mode
dw 360
dw 480
LAST_X_MODE equ 7
ModeTable label word ; Mode X tweak table
dw offset X320Y200
dw offset X320Y240
dw offset X360Y200
dw offset X360Y240
dw offset X320Y400
dw offset X320Y480
dw offset X360Y400
dw offset X360Y480
PARAMS label byte
_CurrXMode dw 0 ; Current graphics mode index
_InGraphics db 0 ; Flag indicating graphics activity
_ScrnPhysicalByteWidth dw 0 ; Logical width in bytes of screen
_ScrnPhysicalPixelWidth dw 0 ; Logical width in pixels of screen
_ScrnPhysicalHeight dw 0 ; Logical Height of screen
_ErrorValue db 0 ; Set after function calls
_SplitScrnActive db 0 ; Flag indicating Split scrn activity
_DoubleBufferActive dw 0 ; Flag indicating double buffering
_SplitScrnScanLine dw 0 ; Split Screen's starting scan line
_SplitScrnVisibleHeight dw 0 ; Split Screen's height on screen
_SplitScrnOffs dw 0 ; Offset in video ram of Split Screen
; always = 0
_Page0_Offs dw 0 ; Ofset in video ram of Main virtual
; screen ( = 0 if no split screen
; otherwise = offset of first byte
; after split screen
_Page1_Offs dw 0 ; Ofset in video ram of Second virtual
; screen ( = 0 if no split screen
; otherwise = offset of first byte
; after split screen
; = Page0_Offs if Doubble buffering
; not enabled
_NonVisual_Offs dw 0 ; Ofset in video ram of first byte
; of non visible ram
_ScrnLogicalByteWidth dw 0 ; Logical width in bytes of screen
_ScrnLogicalPixelWidth dw 0 ; Logical width in pixels of screen
_ScrnLogicalHeight dw 0 ; Logical Height of screen
_MaxScrollX dw 0 ; Max X start position of Physical
; screen within virtual screen (in
; bytes)
_MaxScrollY dw 0 ; Max Y start position of Physical
; screen within virtual screen
_VisiblePageIdx dw 0 ; Index of currently visible D.B.
; page
PageAddrTable label word
_VisiblePageOffs dw 0 ; Table containing starting offsets
_HiddenPageOffs dw 0 ; of the double buffer pages
PARAMS_END label byte
PARAM_COUNT equ ($-PARAMS)
; Index/data pairs for CRT Controller registers that differ between
; mode 13h and mode X.
.code
;Pelpan values for 0,1,2,3 pixel panning to the left, respectively
PelPanMask db 000h,002h,004h,006h
DoubleScanFlag db ? ; Flag to indicate double scanned mode
;-------------------------------------------------------------------------
; Local Logical Screen Width setting function
; cx = Requitrd Logical Width
;
; WARNING: no registers are preserved
SetLogicalScrWidth proc
mov dx,CRTC_INDEX
mov al,CRTC_OFFSET
out dx,al
inc dx
mov ax,cx
cmp ax,[_ScrnPhysicalPixelWidth]; Is logical width >= physical width
jge @@ValidLogicalWidth ; yes - continue
mov ax,bx ; no - set logical width = physical
@@ValidLogicalWidth:
shr ax,3
out dx,al
; The EXACT logical pixel width may not have been possible since
; it should be divisible by 8. Round down to the closest possible
; width and update the status variables
shl ax,1
mov bx,ax
mov [_ScrnLogicalByteWidth],ax ; Store the byte width of virtual
; screen
sub ax,[_ScrnPhysicalByteWidth] ; Calculate and store Max X position
shl ax,2 ; of physical screen in virtual
mov [_MaxScrollX],ax ; screen in pixels
mov ax,bx ; set ax to byte width of virt scrn
shl ax,2 ; convert to pixels
mov [_ScrnLogicalPixelWidth],ax ; store virt scrn pixel width
mov cx,ax ; save ax (return value)
; calculate no. non split screen rows in video ram
mov ax,0ffffh ; cx = Maximum video ram offset
sub dx,dx ; DX:AX is divide operand, set DX = 0
div bx ; divide ax by ScrnLogicalByteWidth
mov [_ScrnLogicalHeight],ax ; Save Screen Logical Height
sub ax,[_ScrnPhysicalHeight] ; Update the maximum Y position of
mov [_MaxScrollY],ax ; Physical screen in logical screen
mov ax,cx ; restore ax (return value)
@@Done: ret
SetLogicalScrWidth endp
;-----------------------------------------------------------------------
; Mode X graphics mode set with a virtual screen
; logical screen width.
; C near-callable as:
;
; int x_set_mode(unsigned int mode,unsigned int WidthInPixels);
;
; returns the actual width of the allocated virtual screen in pixels
; if a valid mode was selected otherwise returns -1
;
; Saves virtual screen pixel width in _ScrnLogicalPixelWidth.
; Saves virtual screen byte width in _ScrnLogicalByteWidth.
; Physical screen dimensions are set in _ScrnPhysicalPixelWidth,
; _ScrnPhysicalByteWidth and _ScrnPhysicalHeight
;
;
; Modes: 0 = 320 x 200 (256 color)
; 1 = 320 x 240 (256 color)
; 2 = 360 x 240 (256 color)
; 3 = 320 x 400 (256 color)
; 4 = 320 x 480 (256 color)
; 5 = 360 x 480 (256 color)
;
; Written by Themie Gouthas,
; parts adapted from M. Abrash code.
;------------------------------------------------------------------------
_x_set_mode proc
ARG mode:word,logicalscrwidth:word
push bp ;preserve caller's stack frame
mov bp,sp
push si ;preserve C register vars
push di ; (don't count on BIOS preserving anything)
cld
mov ax,ds
mov es,ax
mov di,offset PARAMS
xor ax,ax
mov cx,PARAM_COUNT
rep stosb
mov cx,[mode]
cmp cx,LAST_X_MODE ; have we selected a valid mode
jle @@ValidMode ; Yes !
mov [_InGraphics],FALSE ; No return -1
mov ax,-1
pop di
pop si
pop bp
ret
@@ValidMode:
mov [_CurrXMode],cx
mov [_InGraphics],TRUE
xor al,al
cmp cx,3
jg @@SetDoubleScanFlag
mov al,TRUE
@@SetDoubleScanFlag:
mov cs:[DoubleScanFlag],al
mov ax,13h ; let the BIOS set standard 256-color
int 10h ; mode (320x200 linear)
mov dx,SC_INDEX
mov ax,0604h
out dx,ax ; disable chain4 mode
mov ax,0100h
out dx,ax ; synchronous reset while setting Misc
; Output for safety, even though clock
; unchanged
mov bx,offset ModeTable
shl cx,1
add bx,cx
mov si, word ptr [bx]
lodsb
mov dx,MISC_OUTPUT
out dx,al ; select the dot clock and Horiz
; scanning rate
mov dx,SC_INDEX
mov ax,0300h
out dx,ax ; undo reset (restart sequencer)
mov dx,CRTC_INDEX ; reprogram the CRT Controller
mov al,11h ; VSync End reg contains register write
out dx,al ; protect bit
inc dx ; CRT Controller Data register
in al,dx ; get current VSync End register setting
and al,07fh ; remove write protect on various
out dx,al ; CRTC registers
dec dx ; CRT Controller Index
cld
xor cx,cx
lodsb
mov cl,al
@@SetCRTParmsLoop:
lodsw ; get the next CRT Index/Data pair
out dx,ax ; set the next CRT Index/Data pair
loop @@SetCRTParmsLoop
mov dx,SC_INDEX
mov ax,0f02h
out dx,ax ; enable writes to all four planes
mov ax,SCREEN_SEG ; now clear all display memory, 8 pixels
mov es,ax ; at a time
sub di,di ; point ES:DI to display memory
sub ax,ax ; clear to zero-value pixels
mov cx,8000h ; # of words in display memory
rep stosw ; clear all of display memory
; Set pysical screen dimensions
lodsw ; Load scrn pixel width
mov [_ScrnPhysicalPixelWidth],ax ; from tweak table and store
mov [_SplitScrnScanLine],ax ; No splitscrn ==
; splitscrn=PhysicalscrnHeight
mov bx,ax ; Copy width for later use
shr ax,2 ; Convert to byte width
mov [_ScrnPhysicalByteWidth],ax ; Store for later use
lodsw ; Load Screen Phys. Height
mov [_ScrnPhysicalHeight],ax ; Store for later use
; Mode X is set, now set the required logical page width.
mov cx,[logicalscrwidth]
call SetLogicalScrWidth
pop di ;restore C register vars
pop si
pop bp ;restore caller's stack frame
ret
_x_set_mode endp
;----------------------------------------------------------------------
; Mode X (256 color mode) set default access video plane
;
; C near-callable as:
; void x_select_default_plane(unsigned char plane);
;
; Enables Read/Write access to a plane using general memory access
; methods
;
; Written by Themie Gouthas
;----------------------------------------------------------------------
_x_select_default_plane proc
ARG Plane:byte
push bp
mov bp,sp ; set up stack frame
mov cl,byte ptr [Plane]
; SELECT WRITE PLANE
and cl,011b ;CL = plane
mov ax,0100h + MAP_MASK ;AL = index in SC of Map Mask reg
shl ah,cl ;set only the bit for the required
; plane to 1
mov dx,SC_INDEX ;set the Map Mask to enable only the
out dx,ax ; pixel's plane
; SELECT READ PLANE
mov ah,cl ;AH = plane
mov al,READ_MAP ;AL = index in GC of the Read Map reg
mov dx,GC_INDEX ;set the Read Map to read the pixel's
out dx,ax ; plane
pop bp
ret
_x_select_default_plane endp
;----------------------------------------------------------------------
; Mode X (256 color mode) Set Mode X split screen starting row
; The split screen resides on the bottom half of the screen and has a
; starting address of A000:0000
;
; C near-callable as:
; void x_set_splitscreen(unsigned int line);
;
; Updates _Page0_Offs to reflect the existence of the split screen region
; ie _MainScrnOffset is set to the offset of the first pixel beyond the split
; screen region
;
; Written by Themie Gouthas
;----------------------------------------------------------------------
_x_set_splitscreen proc
ARG Line:word
push bp
mov bp,sp ; set up stack frame
push si
xor si,si ; si=0 -> x virtual page start coord
cmp [_DoubleBufferActive],0
jne @@error
cmp [_SplitScrnActive],0
je @@NotPreviouslyCalled
@@error:
mov [_ErrorValue],ERROR
pop si
pop bp ; Return if previously called
ret
@@NotPreviouslyCalled:
; Turn on split screen pal pen suppression, so the split screen
; wo'nt be subject to pel panning as is the non split screen portion.
mov dx,INPUT_STATUS_0
in al,dx ; Reset the AC Index/Data toggle to
; index state
mov al,AC_MODE_CONTROL+20h ; Bit 5 set to prevent screen blanking
mov dx,AC_INDEX ; Point AC to Index/Data register
out dx,al
inc dx ; Point to AC Data reg (for reads only)
in al,dx ; Get the current AC Mode Control reg
or al,20h ; Enable split scrn Pel panning suppress.
dec dx ; Point to AC Index/Data reg (for writes only)
out dx,al ; Write the new AC Mode Control setting
; with split screen pel panning
; suppression turned on
mov [_SplitScrnActive],TRUE
mov ax,[Line]
jns @@NotNeg ; Check that Split Scrn start scan line is +ve
mov ax,0 ; Since -ve set to 0
@@NotNeg:
mov [_SplitScrnScanLine],ax ; save the scanline
mov cl,cs:[DoubleScanFlag]
shl ax,cl ; Mode X 200 and 240 line modes are actually
; 400 and 480 lines that are double scanned
; so for start scanline multiply required ModeX
; scan line by 2 if its a double scanned mode
mov bx,ax ; save the scanline
WaitVsyncStart ; wait for vertical retrace
cli ; Dont allow register setting to be interrupted
mov dx,CRTC_INDEX
mov ah,bl
mov al,LINE_COMPARE
out dx,ax ; Bits 7-0 of the split screen scan line
mov ah,bh
and ah,1
mov cl,4
shl ah,cl
mov al,OVERFLOW ; Bit 4 of overflow register = Bit 8 of split
out dx,al ; screen scan line,
inc dx ; So using readability of VGA registers
in al,dx ; Read the OVERFLOW register, and set the
and al, not 10h ; bit corresponding to Bit 8 (above)
or al,ah
out dx,al
dec dx
mov ah,bh
and al,2
mov cl,3
ror ah,cl
mov al,MAX_SCAN_LINE ; Bit 6 of max scan line register =
out dx,al ; Bit 9 of split screen scan line
inc dx ; As we did before, update the apropriate
in al,dx ; bit without disturbing the rest
and al, not 40h
or al,ah
out dx,al
sti ; Registers are set, so interrupts are safe
mov ax,[_ScrnPhysicalHeight] ; Determine where the first byte
sub ax,[_SplitScrnScanLine] ; of the non split screen video ram
mov [_SplitScrnVisibleHeight],bx ; starts and store it for reference
mov bx,[_ScrnLogicalByteWidth]
mul bx
mov [_Page0_Offs],ax
mov [_Page1_Offs],ax
; calculate no. non split screen rows in video ram
mov cx,0ffffh ; cx = Maximum video ram offset
sub cx,ax ; cx = cx - _Page0_Offs
xchg cx,ax ; swap cx and ax
sub dx,dx ; DX:AX is divide operand, set DX = 0
div bx ; divide ax (prev cx) by
; ScrnLogicalByteWidth
mov [_ScrnLogicalHeight],ax ; Save Screen Logical Height
sub ax,[_SplitScrnScanLine] ; Update the maximum Y position of
mov [_MaxScrollY],ax ; Physical screen in logical screen
xchg cx,ax ; restore original ax (MainScrnOfs)
mov bh,al ; Set the visible screen start address
mov ch,ah ; to the top left corner of the virtual
jmp short StartAddrEntry ; screen
_x_set_splitscreen endp
;-----------------------------------------------------------------------
; Mode X (256 color mode) Page flip primer
; No clipping is performed.
; C near-callable as:
;
; void x_page_flip(unsigned int x, unsigned int y);
;
; Swaps visible and hidden page offsets and then executes the SetStartAddr
; to achieve a page flip.
;
; SEE x_set_start_addr below
;
; Written by Themie Gouthas
;------------------------------------------------------------------------
_x_page_flip proc
ARG x:word,y:word
push bp ;preserve caller's stack frame
mov bp,sp ;point to local stack frame
push si
mov si,[x]
mov ax,[_ScrnLogicalByteWidth] ; Calculate Offset increment
mul [y] ; for Y
cmp [_DoubleBufferActive],TRUE ; Do we have double buffering ?
jne PageFlipEntry1
mov bx,[_HiddenPageOffs]
xchg bx,[_VisiblePageOffs] ; Swap the Page Offsete
xchg [_HiddenPageOffs],bx
xor [_VisiblePageIdx],01h ; Set the Visible page index
jmp short PageFlipEntry2
_x_page_flip endp
;-----------------------------------------------------------------------
; Mode X (256 color mode) Set Mode X non split screen start address
; of logical screen.
; C near-callable as:
;
; void x_set_start_addr(unsigned int x, unsigned int y);
;
; Params: StartOffset is offset of first byte of logical screen ram
; (Useful if you want to double buffer by splitting your non
; split screen video ram into 2 pages)
; X,Y coordinates of the top left hand corner of the physical screen
; within the logical screen
; X must not exceed (Logical screen width - Physical screen width)
; Y must not exceed (Logical screen height - Physical screen height)
;
;
; Written by Themie Gouthas,
; Parts addapted from M. Abrash code published in DDJ Mag.
;------------------------------------------------------------------------
_x_set_start_addr proc
ARG x:word,y:word
push bp
mov bp,sp
push si
mov si,[x]
mov ax,[_ScrnLogicalByteWidth] ; Calculate Offset increment
mul [y] ; for Y
cmp [_DoubleBufferActive],TRUE ; Do we have double buffering ?
je @@PageResolution
PageFlipEntry1:
add ax,[_Page0_Offs] ; no - add page 0 offset
jmp short @@AddColumn
PageFlipEntry2:
@@PageResolution:
add ax,[_VisiblePageOffs] ; Add visible page offset
@@AddColumn:
mov cx,si
shr cx,2
add ax,cx ; add the column offset for X
mov bh,al ; setup CRTC start addr regs and
; values in word registers for
mov ch,ah ; fast word outs
StartAddrEntry:
mov bl,ADDR_LOW
mov cl,ADDR_HIGH
mov dx,INPUT_STATUS_0 ;Waitfor trailing edge of Vsync pulse
@@WaitDE:
in al,dx
test al,01h
jnz @@WaitDE ;display enable is active low (0 = active)
mov dx,CRTC_INDEX
mov ax,bx
out dx,ax ;start address low
mov ax,cx
out dx,ax ;start address high
mov dx,AC_INDEX
mov al,PEL_PANNING+20h ; Point the attribute controller to pel pan
out dx,al ; reg. Bit 5 also set to prevent blanking
and si,0003h ; select pel pan register value for the
mov al,cs:PelPanMask[si] ; required x coordinate
out dx,al ; load new Pel Pan setting.
; Now wait for vertical sync, so the other page will be invisible when
; we start drawing to it.
WaitVsyncStart
; mov dx,INPUT_STATUS_0 ; Now wait for vertical sync, so the other
;@@WaitVS: ; page will be invisible when we start
; in al,dx ; drawing to it.
; test al,08h
; jz @@WaitVS ;vertical sync is active high (1 = active)
mov [_ErrorValue],OK
pop si
pop bp
ret
_x_set_start_addr endp
;-----------------------------------------------------------------------
; Mode X (256 color mode) Mode X split screen hide
; C near-callable as:
;
; void x_hide_splitscreen()
;
; Hides an existing split screen by setting its starting scan line to
; the last physical screen scan line
;
; WARNING: Only to be used if SplitScrnLine has been previously called
; WARNING: DO NOT USE with mode 4-7 (320x400-360x480). The memory for
; the initial split screen is reserved and the size limitations
; of these modes means any change in the split screen scan line
; will encroach on the split screen ram
;
; Written by Themie Gouthas
;------------------------------------------------------------------------
_x_hide_splitscreen proc
push bp
mov bp,sp
cmp [_SplitScrnActive],TRUE
je @@SplitScreenEnabled
@@error:
mov [_ErrorValue],ERROR
pop bp
ret
@@SplitScreenEnabled:
cmp [_CurrXMode],3 ; Do nothing for Modes > 2
jg @@error
mov bx,[_ScrnPhysicalHeight]
mov ax,[_ScrnLogicalHeight]
sub ax,bx
mov [_MaxScrollY],ax
xor ax,ax
mov [_SplitScrnVisibleHeight],ax
mov cl,cs:[DoubleScanFlag] ; Compensate for double scanned modes
shl bx,cl
WaitVsyncStart ; wait for vertical retrace
cli ; Dont allow register setting to be interrupted
mov dx,CRTC_INDEX
mov ah,bl
mov al,LINE_COMPARE
out dx,ax ; Bits 7-0 of the split screen scan line
mov ah,bh
and ah,1
shl ah,4
mov al,OVERFLOW ; Bit 4 of overflow register = Bit 8 of split
out dx,al ; screen scan line,
inc dx ; So using readability of VGA registers
in al,dx ; Read the OVERFLOW register, and set the
and al, not 10h ; bit corresponding to Bit 8 (above)
or al,ah
out dx,al
dec dx
mov ah,bh
and al,2
ror ah,3
mov al,MAX_SCAN_LINE ; Bit 6 of max scan line register =
out dx,al ; Bit 9 of split screen scan line
inc dx ; As we did before, update the apropriate
in al,dx ; bit without disturbing the rest
and al, not 40h
or al,ah
out dx,al
sti ; Registers are set, so interrupts are safe
@@done:
mov [_ErrorValue],OK
pop bp
ret
_x_hide_splitscreen endp
;-----------------------------------------------------------------------
; Mode X (256 color mode) Mode X split screen show
; C near-callable as:
;
; void x_show_splitscreen()
;
; Restores split screen start scan line to the initial split screen
; starting scan line as set by SplitScrnLine.
;
; WARNING: Only to be used if SplitScrnLine has been previously called
; WARNING: DO NOT USE with mode 4-7 (320x400-360x480). The memory for
; the initial split screen is reserved and the size limitations
; of these modes means any change in the split screen scan line
; will encroach on the split screen ram
; Update: Now disabled for these modes
;
; Written by Themie Gouthas
;------------------------------------------------------------------------
_x_show_splitscreen proc
push bp
mov bp,sp
cmp [_SplitScrnActive],TRUE
je @@SplitScreenEnabled
@@error:
mov [_ErrorValue],ERROR
pop bp
ret
@@SplitScreenEnabled:
cmp [_CurrXMode],3 ; Do nothing for Modes > 2
jg @@error
mov bx,[_SplitScrnScanLine]
mov ax,[_ScrnLogicalHeight] ; Update Max Scroll Y
sub ax,bx
mov [_MaxScrollY],ax
mov ax,[_ScrnPhysicalHeight]
sub ax,bx
mov [_SplitScrnVisibleHeight],ax
mov cl,cs:[DoubleScanFlag] ; Compensate for double scanned modes
shl bx,cl
WaitVsyncStart ; wait for vertical retrace
cli ; Dont allow register setting to be interrupted
mov dx,CRTC_INDEX
mov ah,bl
mov al,LINE_COMPARE
out dx,ax ; Bits 7-0 of the split screen scan line
mov ah,bh
and ah,1
shl ah,4
mov al,OVERFLOW ; Bit 4 of overflow register = Bit 8 of split
out dx,al ; screen scan line,
inc dx ; So using readability of VGA registers
in al,dx ; Read the OVERFLOW register, and set the
and al, not 10h ; bit corresponding to Bit 8 (above)
or al,ah
out dx,al
dec dx
mov ah,bh
and al,2
ror ah,3
mov al,MAX_SCAN_LINE ; Bit 6 of max scan line register =
out dx,al ; Bit 9 of split screen scan line
inc dx ; As we did before, update the apropriate
in al,dx ; bit without disturbing the rest
and al, not 40h
or al,ah
out dx,al
sti ; Registers are set, so interrupts are safe
@@Done:
mov [_ErrorValue],0
pop bp
ret
_x_show_splitscreen endp
;-----------------------------------------------------------------------
; Mode X (256 color mode) Modify Mode X split screen starting scan line
; C near-callable as:
;
; void x_adjust_splitscreen(unsigned int ScanLine)
;
; Sets the split screen start scan line to a new scan line. Valid scan lines
; are between the initial split screen starting scan line and the last
; physical screen scan line.
;
; WARNING: Only to be used if SplitScrnLine has been previously called
; WARNING: DO NOT USE with mode 4-7 (320x400-360x480). The memory for
; the initial split screen is reserved and the size limitations
; of these modes means any change in the split screen scan line
; will encroach on the split screen ram
; Update: Now disabled for these modes
;
;
; Written by Themie Gouthas
;------------------------------------------------------------------------
_x_adjust_splitscreen proc
ARG ScanLine
push bp
mov bp,sp
cmp [_SplitScrnActive],TRUE
je @@SplitScreenEnabled
@@error:
mov [_ErrorValue],ERROR
pop bp
ret
@@SplitScreenEnabled:
cmp [_CurrXMode],3 ; Do nothing for Modes > 2
jg @@error
mov bx,[ScanLine] ; Is the required starting scan line
cmp bx,[_SplitScrnScanLine] ; valid ?
js @@Done ; No - Then do nothing
@@ValidScanLine:
mov ax,[_ScrnLogicalHeight] ; Update Max Scroll Y
sub ax,bx
mov [_MaxScrollY],ax
mov ax,[_ScrnPhysicalHeight]
sub ax,bx
mov [_SplitScrnVisibleHeight],ax
mov cl,cs:[DoubleScanFlag] ; Compensate for double scanned modes
shl bx,cl
WaitVsyncStart ; wait for vertical retrace
cli ; Dont allow register setting to be interrupted
mov dx,CRTC_INDEX
mov ah,bl
mov al,LINE_COMPARE
out dx,ax ; Bits 7-0 of the split screen scan line
mov ah,bh
and ah,1
shl ah,4
mov al,OVERFLOW ; Bit 4 of overflow register = Bit 8 of split
out dx,al ; screen scan line,
inc dx ; So using readability of VGA registers
in al,dx ; Read the OVERFLOW register, and set the
and al, not 10h ; bit corresponding to Bit 8 (above)
or al,ah
out dx,al
dec dx
mov ah,bh
and al,2
ror ah,3
mov al,MAX_SCAN_LINE ; Bit 6 of max scan line register =
out dx,al ; Bit 9 of split screen scan line
inc dx ; As we did before, update the apropriate
in al,dx ; bit without disturbing the rest
and al, not 40h
or al,ah
out dx,al
sti ; Registers are set, so interrupts are safe
@@Done:
mov [_ErrorValue],OK
pop bp
ret
_x_adjust_splitscreen endp
;-----------------------------------------------------------------------
; Mode X (256 color mode) Enable DoubleBuffering on non split screen area
; C near-callable as:
;
; int x_set_doublebuffer(unsigned int PageHeight);
;
; Params: PageHeight is the height of the virtual screen to double buffer
; Returns the closest possible height to the specified.
;
; Sets up two double buffering virtual pages
; GLOBAL variables set:
;
; _Page1_Offs Offset of second virtual page
; _NonVisual_Offs Offset of first non visible video ram byte
; _DoubleBufferActive Flag
; _PageAddrTable Table of Double buffering pages start offsets
; _ScrnLogicalHeight Logical height of the double buffering pages
;
;
; Written by Themie Gouthas
;------------------------------------------------------------------------
_x_set_doublebuffer proc
ARG PageHeight:word
push bp
mov bp,sp
cmp [_DoubleBufferActive],0
je @@OkToContinue
@error:
mov [_ErrorValue],ERROR
pop bp
ret
@@OkToContinue:
mov [_VisiblePageIdx],0 ; Set visible Page to 0
mov ax,[_ScrnLogicalHeight] ; Set Maximum D.B. Page height to
shr ax,1 ; _ScrnLogicalHeight / 2
mov bx,[PageHeight] ; Is the require D.B. Page Height
cmp ax,bx ; > the Maximum D.B. Page Height ?
js @@InvalidHeight ; no - jump
mov ax,bx ; yes - Set the D.B. Page height to
; to the maximum allowed.
@@InvalidHeight:
mov [_ScrnLogicalHeight],ax ; Update logical screen height to
; reflect the height of a D.B. page
mov dx,ax
mul [_ScrnLogicalByteWidth] ; Calculate the offset of the second
mov cx,ax ; D.B. Page in video ram
mov bx,[_Page0_Offs]
mov [_VisiblePageOffs],bx
add ax,bx
mov [_Page1_Offs],ax ; Save it
mov [_HiddenPageOffs],ax
add ax,cx ; Calculate the offset of first byte
mov [_NonVisual_Offs],ax ; beyond the D.B. pages and save it
mov [_DoubleBufferActive],TRUE ; Set flag indicating D.B'ing mode on
mov ax,dx
sub ax,[_ScrnPhysicalHeight]
add ax,[_SplitScrnVisibleHeight]
mov [_MaxScrollY],ax
mov ax,dx ; return the D.B. pages' height
mov [_ErrorValue],OK
pop bp
ret
_x_set_doublebuffer endp
;----------------------------------------------------------------------
; Return to text mode
;
_x_text_mode proc
push bp
mov ax,03h ; Restore Text Mode
int 10h
pop bp
ret
_x_text_mode endp
end
