; Screen saver (blanks screen)
; Only works in 80x25 screen modes (2,3,7) [could easily be adapted/others]

.SEQ          ; store segment sequentially as they appear
.286          ; use 80286+ code
.MODEL tiny   ; TINY model to make it a .COM program

;* Macros *

StAlloc MACRO sizew    ; macro to allocate stack, size "sizew" words
 MOV BX,((sizew*2)+15) SHR 4    ; BX = size in paragraphs
 MOV AH,48h        ; allocate memory function
 INT 21h           ; call DOS
 CLI               ; freeze interrupts
 MOV SS,AX         ; set stack segment to allocated segment returned in AX
 MOV SP,sizew*2-2  ; set stack pointer to end of segment (goes top down)
 STI               ; restore interrupts
ENDM

StDeAlloc MACRO     ; macro to deallocate stack
 MOV AX,SS
 MOV ES,AX
 MOV AH,49h       ; call DOS deallocate block function
 INT 21h
ENDM


;* Code Segment *

code SEGMENT PARA PUBLIC 'CODE'    ; code segment
ASSUME CS:code, DS:code, ES:code, SS:code  ; assume CS->"code" etc.
ORG 100h                           ; start assembling at offset 0h (default)

;* Program Start *

start:                             ; label for start of program
 JMP init

;* Procedures *

; Save screen and display (init) screen saver logo

ScreenSaver PROC NEAR
 MOV AX,CS
 MOV ES,AX
 MOV DI,OFFSET ScrData
 MOV DS,CS:ScrAddress
 XOR SI,SI
 CLD
 MOV CX,2000
 REP MOVSW         ; save screen
 MOV CS:SSOn,1
 MOV AH,0Fh
 INT 10h           ; get current page in BH
 MOV AH,03h
 INT 10h           ; get old cursor size
 MOV CS:OldCursor,CX
 MOV AH,01h
 MOV CX,0100h
 INT 10h           ; hide cursor
 CALL RunSaver     ; clear screen
 CALL DrawSaver    ; draw logo
 RET
ENDP


; Restore screen and deinitialize screen saver

RemoveSaver PROC NEAR
 MOV ES,CS:ScrAddress
 XOR DI,DI
 MOV AX,CS
 MOV DS,AX
 MOV SI,OFFSET ScrData
 CLD
 MOV CX,2000
 REP MOVSW
 MOV CS:SSOn,0
 MOV AH,01h
 MOV CX,CS:OldCursor
 INT 10h           ; restore cursor
 RET
ENDP


; Re-hide screen to cover any writing

RunSaver PROC NEAR
 MOV ES,CS:ScrAddress
 XOR DI,DI
 MOV CX,2000
 XOR AX,AX
 REP STOSW
 RET
ENDP


; Find parts of screen that were changed and save to virtual screen

DeltaSaver PROC NEAR
 CLD
 MOV DS,CS:ScrAddress
 XOR SI,SI            ; DS:SI -> physical screen
 MOV AX,CS
 MOV ES,AX
 MOV DI,OFFSET ScrData  ; ES:DI -> virtual screen
 XOR BH,BH            ; row 0
ds_nextrow:
 MOV CX,80
 CMP BH,CS:Row
 JZ ds_check          ; if row of copyright string handle separately
ds_loop:
 LODSW
 CMP AX,0             ; check if still zero (as set by screen saver)
 JZ ds_again
 MOV ES:[DI],AX       ; set to new value
ds_again:
 INC DI
 INC DI
 LOOP ds_loop
ds_new:
 INC BH
 CMP BH,25
 JNZ ds_nextrow
 RET
ds_check:
 MOV BP,OFFSET Copyright
 MOV BL,CS:Colour
ds_loop2:
 LODSW
 CMP AL,ES:[BP]
 JNZ ds_delta
 CMP AH,BL
 JZ ds_ok
ds_delta:
 MOV ES:[DI],AX
ds_ok:
 INC DI
 INC DI
 INC BP
 LOOP ds_loop2
 JMP SHORT ds_new
ENDP


; Draw copyright string

DrawSaver PROC NEAR
 MOV AX,WORD PTR CS:Row2
 MOV WORD PTR CS:Row,AX  ; now safe to copy incremented data
 MOV AH,CS:Row
 MOV AL,160
 MUL AH
 MOV DI,AX
 MOV AX,CS
 MOV DS,AX
 MOV SI,OFFSET CS:Copyright
 MOV AH,CS:Colour
ds_write:
 LODSB
 OR AL,AL
 JZ ds_donemsg
 STOSW
 JMP SHORT ds_write
ds_donemsg:
 RET
ENDP


; move message and change colour

IncSaver PROC NEAR
 MOV AX,WORD PTR CS:Row2  ; AL = row, AH = attribute
 ADD AX,101h              ; increment both
 CMP AL,25
 JNZ is_rowset
 XOR AL,AL
is_rowset:
 CMP AH,16
 JNZ is_colset
 MOV AH,1
is_colset:
 MOV WORD PTR CS:Row2,AX
 RET
ENDP


; INT 09h interrupt handler
; checks for hotkey combinations and deinstalls or activates program if found

Int09Handler PROC FAR
 PUSHF
 CALL CS:OldInt09      ; call old handler
 PUSHA
 PUSH DS
 PUSH ES
 MOV AX,40h
 MOV ES,AX
 MOV DI,ES:[1Ah]
 CMP DI,ES:[1Ch]       ; quit if no keys in keyboard buffer
 JZ i9_exit
 MOV CS:SSTimer,0      ; zero timer for screen saver
 CMP CS:SSOn,0
 JZ i9_skip
 CALL RemoveSaver      ; if screen saver active, restore screen
i9_skip:
 MOV DI,ES:[DI]        ; get key in keyboard buffer
 CMP DI,4400h          ; check for F10
 JNZ i9_exit
 PUSH DI
 PUSH ES
 CALL ScreenSaver      ; startup screen saver
 POP ES
 POP DI
i9_remove:
 INC WORD PTR ES:[1Ah]
 INC WORD PTR ES:[1Ah] ; remove key from buffer
 CMP WORD PTR ES:[1Ah],3Eh
 JNZ i9_exit
 MOV WORD PTR ES:[1Ah],1Eh      ; wrap around if required
i9_exit:
 POP ES
 POP DS
 POPA
 IRET
ENDP


; INT 1Ch interrupt handler
; activates screen saver when timeout occurs

Int1CHandler PROC FAR
 PUSHF
 CALL CS:OldInt1C
 PUSHA
 PUSH DS
 PUSH ES
 CMP CS:SSOn,0
 JZ i1c_off
 CALL DeltaSaver      ; store changes to virtual screen
 CALL RunSaver        ; blank screen
 CALL DrawSaver       ; draw message or graphic
i1c_off:
 MOV AL,CS:Timer1
 DEC AL
 MOV CS:Timer1,AL
 JNZ i1c_exit
 MOV AH,18
 MOV AL,CS:Timer2
 DEC AL
 JNZ i1c_not19
 INC AH
 MOV AL,5
i1c_not19:
 MOV CS:Timer2,AL
 MOV CS:Timer1,AH
 CMP CS:SSOn,0
 JZ i1c_count
 CALL IncSaver
 JMP SHORT i1c_exit
i1c_count:
 MOV AX,CS:SSTimer
 INC AX
 MOV CS:SSTimer,AX
 CMP AX,180           ; 3 minutes
 JNZ i1c_exit
 XOR AX,AX
 MOV CS:SSTimer,AX    ; set to zero
 CALL ScreenSaver     ; startup screen saver
i1c_exit:
 POP ES
 POP DS
 POPA
 IRET
ENDP


;* Data Area *

; TSR data

ScrAddress DW 0
OldCursor  DW 0
OldInt09   DD 0
OldInt1C   DD 0
SSTimer    DW 0
SSOn       DB 0
Timer1     DB 18
Timer2     DB 5
ScrData    DW 2000 DUP (?)
Row        DB 0
Colour     DB 1
Row2       DB 0
Colour2    DB 1
Copyright  DB '  VORTEX screen saver (c)1994 Vortex Systems Inc . '
     DB 'Created by Overlord [FV',39,'95]  ',0
Sig        DB 'VXSS'

TSR_end LABEL BYTE


;* Main Program *

init:
 MOV AX,CS
 MOV DS,AX
 MOV ES,AX
 MOV BX,OFFSET code_end
 ADD BX,15
 SHR BX,4
 MOV AH,4AH
 INT 21H                         ; free unneeded memory given to program
 StAlloc 50h                     ; allocate stack (saves memory on disk)
 XOR AX,AX
 MOV ES,AX
 PUSH DS
 MOV DS,ES:[26h]
 CMP WORD PTR DS:Sig,'XV'
 JNZ i_skip
 CMP WORD PTR DS:Sig+2,'SS'
 JNZ i_skip
 MOV AX,WORD PTR DS:OldInt09
 MOV BX,WORD PTR DS:OldInt09+2
 CLI
 MOV ES:[24h],AX
 MOV ES:[26h],BX
 MOV AX,WORD PTR DS:OldInt1C
 MOV BX,WORD PTR DS:OldInt1C+2
 MOV ES:[70h],AX
 MOV ES:[72h],BX
 STI
 MOV AX,DS
 MOV ES,AX
 MOV AH,49h
 INT 21h
 POP DS
 MOV AH,09h
 MOV DX,OFFSET Deinstall
 INT 21h
 StDeAlloc
 MOV AX,4C00h
 INT 21h
i_skip:
 POP DS
 MOV AX,0B800h
 CMP BYTE PTR ES:[0449h],7       ; check if current mode @ 0:449 is 7 (mono)
 JNZ i_gotmode
 MOV AX,0B000h
i_gotmode:
 MOV ScrAddress,AX               ; store screen address
 MOV AX,ES:[24h]
 MOV BX,ES:[26h]
 MOV WORD PTR OldInt09,AX
 MOV WORD PTR OldInt09+2,BX      ; save old interrupt 09h
 MOV AX,OFFSET Int09Handler
 MOV BX,CS
 CLI
 MOV ES:[24h],AX
 MOV ES:[26h],BX
 STI
 MOV AX,ES:[70h]
 MOV BX,ES:[72h]
 MOV WORD PTR OldInt1C,AX
 MOV WORD PTR OldInt1C+2,BX      ; save old interrupt 1Ch
 MOV AX,OFFSET Int1CHandler
 MOV BX,CS
 CLI
 MOV ES:[70h],AX
 MOV ES:[72h],BX
 STI
 MOV AH,49h
 MOV ES,CS:[2Ch]
 INT 21h                         ; deallocate environment block
 MOV AH,09h
 MOV DX,OFFSET Install
 INT 21h                         ; display message
 StDeAlloc                       ; deallocate stack
 MOV DX,OFFSET TSR_end
 ADD DX,15
 SHR DX,4
 MOV AX,3100h
 INT 21h                         ; go TSR, exit with errorlevel 0

;* Data Area *

; main program data

Install     DB 13,10,'Vortex Screen Saver now installed - press F10 to '
    DB 'activate.',13,10,10,'$'
Deinstall   DB 13,10,'Vortex Screen Saver deinstalled Ok.',13,10,10,'$'

;* End Program *

code_end LABEL BYTE                ; mark end of code segment (end of program)
code ENDS                          ; end code segment "code"
END start                          ; end program, start execution at "start:"
