Shareware Grab Bag/Shareware Grab Bag.iso/090/pctjag86.arc/SPRITES2.ASM

Assembly Source File | 1986-05-27 | 20.1 KB | 615 lines

;
; *** Listing 2 ***
;
;These routines produce the effect of hardware sprites in software
; on IBM PC compatible computers. They put objects onto the screen
; in a manner which preserves the background, and produces no
; undesirable fringe or overlap effects. Operations which affect
; video buffer memory are performed as much as possible during
; video non-display periods to avoid other undesirable effects.
;
; Entry points and parameters:
;
;   Initialize - Sets the background buffer address to be used to erase
;    objects, resets internal flags and queue, and on EGAs
;    sets up the use of the vertical interrupt to drive the
;    drawing routines.
;
;    Inputs    - AX holds paragraph address of background buffer.
;    Outputs - None.
;
;   Terminate  - Resets the EGA vertical interrupt hardware and vector
;
;    Inputs    - None.
;    Outputs - None.
;
;   Object_services - Sets X,Y and Form address for a given object
;    to be drawn, and activates or deactivates the object.
;
;    Inputs    - CX holds X position in bytes (0-79) of upper
;           left hand corner of object. 0 is leftmost.
;        - BX holds Y position in lines (0-198) 0 is top.
;           BX must be even! Objects cannot start on odd lines.
;           Objects must also be an even number of lines high.
;        - DI holds object number. Higher numbered objects
;           will appear to be in front of lower numbered
;           objects when they overlap.
;        - SI holds the offset in the code segment of the form
;           to be drawn for the object. A value of 0ffffh means
;           that the object is to be erased, then ignored.
;           Forms must be in the following format:
;
;              byte 0 - height in lines (h)
;              byte 1 - width in bytes  (w)
;              followed by w X h (mask word, image word) pairs.
;
;    Outputs - None.
;
;    Registers - All are saved, except flags
;
;    Warning - No bounds checking is done. X,Y or object numbers
;           out of range can send your program into hyperspace.
;
;   Put_objects_on_screen - This routine should be called by a program
;    running on a CGA to put the objects on the screen. It must be
;    far-called as if it were an interrupt routine. For example:
;
;               pushf
;               call far ptr put_objects_on_screen
;
;    For best results this routine should be called immediately
;     upon the sensing of vertical retrace.
;
;    Inputs    - None.
;    Outputs - None.
;
; Vert_int_modulo_count - This memory word is incremented each time
;   the objects are put into the screen map. On EGAs it can be used
;   to synchronize a program to the constant time base provided by
;   the vertical interrupt.
;
;The flag below must be set properly before assembling this program
;
ega    equ  0         ;1 to assemble for Enhanced Graphics Adapter
             ;0 to assemble for Color Graphics Adapter
cga    equ  (ega xor 1) ;the opposite status of ega
;
bios_data_segment segment at 40h    ;BIOS keeps its data at 400h;
    org    63h            ;at 463h is a word that holds
bios_crtc_base_address    dw    ?    ; the CRT controller's base
bios_data_segment ends            ; address
;
;
cseg    segment para public 'cseg'
    assume    cs:cseg,ds:cseg,es:nothing
    public    initialize,terminate,object_services
    public    put_objects_on_screen,vert_int_modulo_count
;
;Memory for the parameters used to keep track of objects is reserved
; below. Many of the parameters stored are very code specific so that
; the size and number of objects which could be processed during
; vertical non-display time could be maximized.
;
number_of_objects equ    3  ;this should be set to the maximum number
               ; of objects or priorities which will
               ; need to be kept track of at one time.
;
queue label word
;
draw_screen_offset    dw ?  ;offset in screen memory buffer of upper
                  ; left hand corner of object. 0ffffh if
                  ; object is to be ignored.
dist_to_odd_scan_line    dw ?  ;distance from end of object on an even
                  ; scan line to the start of the object
                  ; on the next (odd) scan line
dist_to_even_scan_line    dw ?  ;distance from end of object on an odd
                  ; scan line to the start of the object
                  ; on the next (even) scan line
;
erase_parms label word
;
erase_width         dw ?  ;the object's screen image width in words
erase_entry_point    dw ?  ;the address of the inline code to do erase
erase_screen_offset  dw ?  ;the address where object was last drawn
               ; 0ffffh if object is not to be erased.
erase_image_offset   dw ?  ;used to determine if need to erase when
               ; object is in old position
;
length_of_erase_parms equ $-erase_parms
;
draw_col_entry_point dw ?  ;address of the column code for drawing
draw_row_entry_point dw ?  ;address of the row inline code for drawing
draw_image_offset    dw ?  ;offset in the code segment of the image
;
queue_item_length equ ($ - queue) ;number of bytes for each item
distance_from_entry_point_to_next_item equ $ - erase_entry_point
distance_from_image_to_next_item equ $ - draw_image_offset
;
    db    (  (number_of_objects-1) * queue_item_length ) dup(?)
end_of_queue label word
;
vert_int_modulo_count    dw 0  ;incremented each time a vertical
                  ; interrupt occurs
background_segment    dw ?  ;place to hold the paragraph address
                  ; of the background buffer used to
                  ; erase objects
crtc_base_address    dw ?  ;will hold register address
;
old_int10_offset    dw ?  ;place to store the vector contents
old_int10_segment    dw ?  ; so they can be restored when finished
;
old_int_mask        db ?  ;place to store the mask register's
                  ; contents so it can be restored
;
true    equ    1  ;used for flag values
false    equ    0  ;
;
need_to_draw_something_flag db false ;true if a change needs to be
                     ; made to any of the objects'
                     ; screen images
;
screen_buffer_paragraph_adr equ 0b800h
;
;
initialize proc near
    cld                   ;count up
    push    ds               ;
    mov    cs:[background_segment],ax ;store background adr
    mov    ax,cs               ;make data segment
    mov    ds,ax               ; same as code segment
                       ; since that is where data
    mov    es,ax               ; used by this routine is
    mov    di,offset queue        ;turn off all objects
    mov    cx,(number_of_objects * queue_item_length)/2
    mov    ax,0ffffh           ;
    rep stosw               ;
;
    mov    [need_to_draw_something_flag],false ;nothing to draw
if ega
    sub    ax,ax                ;swapping interrupt
    mov    ds,ax                ; vectors with our
    mov    bx,(10*4)            ; interrupt handler
    mov    ax,offset put_objects_on_screen ;our vertical int
    mov    dx,cs                ; handler address
    cli                    ;disable interrupts
    xchg    [bx],ax             ;offset
    xchg    [bx+2],dx            ;segment
    mov    cs:[old_int10_offset],ax    ;save old value so we
    mov    cs:[old_int10_segment],dx    ; can restore it upon
;                        ; termination
    mov    ax,bios_data_segment        ;find the register
    mov    ds,ax                ; address
    assume    ds:bios_data_segment        ;
    mov    dx,[bios_crtc_base_address]    ;
    mov    cs:[crtc_base_address],dx    ;save it in code seg
    mov    al,11h                ;select vertical
    out    dx,al                ; retrace end register
    mov    al,04h                ; and flip it off
    inc    dx                ;
    out    dx,al                ;
    mov    al,14h                ; then flip it on
    out    dx,al                ;
;
    in    al,21h                ;enable IRQ2
    mov    cs:[old_int_mask],al        ; save old value
    and    al,not 4            ;
    out    21h,al                ;
;
    sti                    ;enable interrupts
endif
    pop    ds                ;restore data segment
    ret
initialize endp
;
terminate    proc    near   ;only needs to be used when assembled
if ega                   ; for use on an EGA
    mov    dx,[crtc_base_address]
    mov    al,11h
    out    dx,al
    inc    dx
    mov    al,24h           ;bit 5 high to disable, bit 4 low to
    out    dx,al           ; clear vertical interrupt
    push    ds
    sub    ax,ax              ;restore original interrupt
    mov    ds,ax              ; 10 vector
    mov    bx,(10*4)          ;
    mov    ax,cs:[old_int10_offset]  ;
    mov    dx,cs:[old_int10_segment] ;
    cli                  ;make sure interrupt
    mov    [bx],ax           ; doesn't occur while
    mov    [bx+2],dx          ; there is an inconsistant
                      ; vector/mask
    mov    bl,cs:[old_int_mask]      ;restore IRQ2 mask bit
    and    bl,4              ; to state it had when
    in    al,21h              ; Initialize was called
    and    al,not 4          ;
    or    al,bl              ;
    out    21h,al              ;
    sti
    pop    ds
endif
    ret
terminate endp
;
object_services proc near
    cld            ;
    push    es        ;save the registers used
    push    ds        ;
    push    ax        ;
    push    bx        ;
    push    cx        ;
    push    si        ;
    push    di        ;
;
    mov    ax,cs        ;everything will be in code segment
    mov    es,ax        ;
    mov    ds,ax        ;

;
    shl    di,1        ;multiply object number
    shl    di,1        ; which is in DI by 20 to
    mov    ax,di        ; find object's parameter table
    shl    di,1        ; offset in queue structure
    shl    di,1        ; (NOTE: If a code change alter
    add    di,ax        ;  queue_item_length this code must
;                ;  be changed!)
    mov    ax,offset queue ;point directly to object's first
    add    di,ax        ; parameter
    mov    ax,[bx+even_line_screen_offset_table]
    add    ax,cx        ;find screen offset of top left corner
if ega
    cli     ;can't allow parameters to be just half
         ; changed if a vertical interrupt occurs
endif
    cmp    si,0ffffh    ;if object is to be turned off then
    jne    save_position    ; need to store a 0ffffh for the draw
    mov    ax,si        ; screen position
    stosw            ;
    jmp short finish_services
save_position:            ;
    stosw         ;save as first parameter (draw_screen_offset)
    lodsb         ;get the height of the image
    xor    ah,ah     ;make height a word
    mov    bx,ax     ;store height
    lodsb         ;get the width of the image in bytes
    mov    cx,2000h ;calculate amount to add after even scan
    sub    cx,ax     ; lines are drawn to get the address of the
    xchg    ax,cx     ; next scan line, and store it in queue
    stosw         ;
    mov    ax,1fb0h ;calculate amount to subtract after odd scan
    add    ax,cx     ; lines are drawn to get the address of the
    stosw         ; next scan line, and store it in queue
    mov    ax,cx     ;store the width in queue
    shr    ax,1     ; width is stored as number of words
    stosw         ;
    mov    ax,[bx+erase_inline_vector_table-2]
             ;-2 because there is no 0 lines entry point
    stosw         ;store the place to jump to erase an image
             ; of this height
    add    di,4     ;skip erase_screen_offset and
             ; erase_image_offset as these are filled
             ; in when an object is drawn
    xchg    si,cx     ;swap image offset with width
    mov    ax,[si+column_inline_vector_table-2] ;inline code adr
    stosw         ; driver operates with words, so there is no
             ; need to divide SI by two to do table lookup
    mov    ax,[bx+row_inline_vector_table-2] ;inline code adr
    stosw         ; which calls column inline code for each row
    mov    [di],cx  ;last param to put on queue is image offset
;
finish_services:
    mov    [need_to_draw_something_flag],true ;record change
if ega
    sti         ;all parameters have been put on queue
             ; so interrupts are safe now
endif
    pop    di     ;restore those registers that were used
    pop    si     ;
    pop    cx     ;
    pop    bx     ;
    pop    ax     ;
    pop    ds     ;
    pop    es     ;
    ret         ;
object_services endp
;
;This table is used to find the offset of an even scan line in the
; memory map of the color graphics adapter in medium resolution mode.
;
even_line_screen_offset_table label word
xx=0
    rept    100    ;there are 100 even lines
    dw    xx*50h    ; each is 50h (80 decimal) long
xx=xx+1
    endm
;
use_old_vector:
    pop    ax    ;restore registers used before
    pop    dx    ; jumping to previous IRQ2 handler
    jmp dword ptr cs:[old_int10_offset]
;
put_objects_on_screen proc far
    push    dx    ;save registers used by EGA code
    push    ax    ;
if ega
            ;must check if interrupt is being signaled
            ; by the EGA card. If not, it needs to be
    mov    dx,3c2h ; handled by another routine in the vector
    in    al,dx    ; chain. The PC AT in particular uses
    test    al,80h    ; IRQ2 for multiple devices.
    jz    use_old_vector
endif
    inc    cs:[vert_int_modulo_count]     ;count vert interrupts
    sti                       ;enable interrupts
    cmp    cs:[need_to_draw_something_flag],true ;anything to do?
    je    process_queue               ; jmp if there is
                           ; otherwise do nothing
if ega
    cli
    mov    al,20h    ;issue a non_specific EOI (End Of Interrupt)
    out    20h,al    ; so that interrupt controller chip will
            ; acknowledge future vertical interrupts
    mov    dx,cs:[crtc_base_address] ;re-enable ega card interrupt
    mov    al,11h    ; select vertical retrace end
    out    dx,al    ; register and clear vertical interrupt
    mov    al,04h    ;
    inc    dx    ;
    out    dx,al    ;
    mov    al,14h    ; then enable vertical interrupt
    out    dx,al    ;
endif
    pop    ax    ;restore original values
    pop    dx    ;
    iret
;
skip_this_object:
    add    si,queue_item_length         ;point SI to next item
    cmp    si,offset end_of_queue         ;see if we are done
    je    draw                 ; jmp to draw if we are
    jmp    get_next_objects_screen_adr  ; if not, erase next
;
process_queue:
    push    bx    ;save the rest of the world
    push    cx    ;
    push    bp    ;
    push    si    ;
    push    di    ;
    push    ds    ;
    push    es    ;
;
    push    cs    ;setup environment
    pop    ds    ; data is in code segment
    cld        ; we will count up
    mov    ax,screen_buffer_paragraph_adr
    mov    es,ax    ; ES points to screen memory
;
    mov    si,offset queue ;point to beginning of queue
;
;Erase all the active objects which have old screen positions
; different from their present screen position or have different
; image offsets
;
get_next_objects_screen_adr:
    mov    ax,[si+erase_screen_offset-draw_screen_offset]
                  ; get the screen buffer
                  ; offset of last draw
    cmp    ax,0ffffh      ;if ffffh then object is
    je    skip_this_object  ; yet to be drawn
    cmp    ax,[si]       ;if new and old positions and
    jne    erase_this_object ; images are same then skip erase
    mov    di,[si+erase_image_offset-draw_screen_offset]
    cmp    di,[si+draw_image_offset-draw_screen_offset]
    je    skip_this_object  ;
erase_this_object:
    inc    si          ;point to next parameter
    inc    si          ;
    mov    di,ax          ;save screen buffer adr
    lodsw              ;get distance to odd scan line
    mov    bp,ax          ; save in BP for inline code use
    lodsw              ;get distance to even scan line
    mov    dx,ax          ; save in DX for inline code use
    lodsw              ;get the width in words for erase
    mov    cx,[si]       ;get address of erase inline code
;
    push    si          ;save position so next object
    push    ds          ; can be found
    mov    ds,[background_segment] ;stuff to erase with
    call    cx          ;erase it!
    pop    ds          ;restore where
    pop    si          ; we left off in queue
    add    si,distance_from_entry_point_to_next_item ;next item
    cmp    si,offset end_of_queue         ;see if we are done
    jne    get_next_objects_screen_adr  ; jmp if more to erase
;
;Draw all the active objects by AND/ORing into screen buffer
;
draw:
    mov    si,offset queue   ;point to beginning of queue
;
get_next_objects_screen_adr2:
    lodsw              ;get screen buffer offset
    mov    [si+erase_screen_offset-draw_screen_offset-2],ax
                  ;save what will be old position
    mov    di,[si+draw_image_offset-draw_screen_offset-2]
                  ;save what will be old image offset
    mov    [si+erase_image_offset-draw_screen_offset-2],di
    cmp    ax,0ffffh      ;see if object is active
    je    skip_this_object2 ; jmp if it isn't
    mov    di,ax          ;save screen buffer adr
    lodsw              ;get distance to odd scan line
    mov    bp,ax          ; save in BP for inline code use
    lodsw              ;get distance to even scan line
    mov    dx,ax          ; save in DX for inline code use
    add    si,length_of_erase_parms ;skip the erase parameters
    lodsw              ;get the draw inline row adr
    mov    cx,ax          ; save in CX for inline use
    lodsw              ;get the draw inline row adr
    mov    bx,ax          ; save in BX for call to inline
    lodsw              ;get draw_image offset
    push    si          ;save pointer to next queue item
    mov    si,ax          ;save draw image in SI
    call    bx          ;draw it!
    pop    si          ;restore where we left off in queue
    cmp    si,offset end_of_queue         ;see if we are done
    jne    get_next_objects_screen_adr2 ; jmp if more to erase
;
finish_up:
if ega
    cli
    mov    al,20h    ;issue a non_specific EOI (End Of Interrupt)
    out    20h,al    ; so that interrupt controller chip will
            ; acknowledge future vertical interrupts
    mov    dx,cs:[crtc_base_address] ;re-enable interrupt
    mov    al,11h    ; select vertical retrace end
    out    dx,al    ;  register and clear vertical interrupt
    mov    al,04h    ;
    inc    dx    ;
    out    dx,al    ;  then enable vertical interrupt
    mov    al,14h    ;
    out    dx,al    ;
endif
    pop    es    ;restore all registers
    pop    ds    ;
    pop    di    ;
    pop    si    ;
    pop    bp    ;
    pop    cx    ;
    pop    bx    ;
    pop    ax    ;
    pop    dx    ;
    mov    cs:[need_to_draw_something_flag],false
            ;indicate no reason to    draw again until the
            ; queue is changed
    iret        ;restore flags and contine where interrupted
;
skip_this_object2:
    add    si,(queue_item_length-2)     ;point SI to next item
    cmp    si,offset end_of_queue         ;see if we are done
    jne    get_next_objects_screen_adr2 ; jmp if not
    jmp short finish_up             ; jmp if all finished
put_objects_on_screen endp
;
;
;This is inline code for finding the screen address for each line
; of the image and calling the AND-OR inline code.
;
rlabel     macro     xx    ;this macro is used to label the inline code
rline&xx&:        ; entry points
    endm
;
;
; inline code for rows
;
xx=42            ;there will be an entry point for each even
            ; number of lines between 2 and 40. They will
            ; be labeled "rline2", "rline4", ... "rline40"
    rept    20    ;each repeat handles two lines
xx=xx-2         ;calculate number of lines for entry point
    rlabel    %xx    ;put in label for entry point

    call    cx    ;CX holds address of inline columns code
    add    di,bp    ;calculate the address to start next line
    call    cx    ;process image for odd scan line
    sub    di,dx    ;calculate the address to start next line
    endm        ; the next line will be an even line
    ret
;
;Inline code for AND-ORing a line of the image into the screen
;
clabel     macro    xx    ;this macro is used to label the inline code
cline&xx&:        ; entry points for number of columns to AND-OR
    endm        ;
;
xx=10            ;this code can handle an image up to ten words
    rept    10    ; wide
    clabel    %xx    ;put in label for entry based on number of
            ; words in a column
    lodsw           ;get mask word
    and    ax,es:[di] ;mask out background
    or    ax,[si]    ;insert data word
    inc    si       ;point to next mask word
    inc    si       ;
    stosw           ;return modified word to memory
xx=xx-1            ;adjust label number
    endm
    ret           ;this return is executed at the end of every
               ; line
;
;This table is used as an indirect address for jumping into
; the inline code for image moving.
;
row_inline_vector_table label word ;there is no entry point for zero
                   ; lines. Starting at 2 eliminates
                   ; the need to store a dummy entry
                   ; point address
row_entry_address   macro   xx       ;this macro is used to generate
        dw    rline&xx&  ; the labels corresponding to the
        endm           ; inline code entry points
;
xx=2
    rept    20
    row_entry_address    %xx
xx=xx+2
    endm
;
;This table is used as an indirect address for jumping into
; the inline code for exclusive-ORing columns.
;
column_inline_vector_table label word ;there is no entry point for zero
                      ; lines. Starting at 2 eliminates
                      ; the need to store a dummy entry
                      ; point address
column_entry_address   macro   xx     ;this macro is used to generate
         dw     cline&xx&    ; the labels corresponding to the
         endm             ; inline code entry points
;
xx=1
    rept    10
    column_entry_address   %xx
xx=xx+1
    endm
;
;This is inline code for erasing the image by restoring the screen
; memory map from the background buffer.
;
elabel    macro    xx    ;this macro is used to label the inline code
eline&xx&:        ; entry points
    endm
;
xx=42            ;there will be an entry point for each even
            ; number of lines between 2 and 40. They will
            ; be labeled "eline2", "eline4", ... "eline40"
    rept    20
xx=xx-2         ;calculate number of lines for this entry point
    elabel  %xx     ;put in label for entry point
    mov     si,di   ;erase using same offset in background buffer
    mov     cx,ax   ;put width of image in words in CX to prepare for
    rep     movsw   ; repeated move string on even line
    add     di,bp   ;calculate address of next line DI + (2000h-width)
    mov     si,di   ;erase using same offset in background buffer
    mov     cx,ax   ;put width of image in bytes in CX to prepare for
    rep     movsw   ; repeated move string on odd line
    sub     di,dx   ;calculate address of next line DI - (1fb0h+width)
    endm
    ret
;
;This table is used as an indirect address for jumping into
; the inline code for erasing an image.
;
erase_inline_vector_table label word ;there is no entry point for zero
                     ; lines. Starting at 2 eliminates
                     ; the need to store a dummy entry
                     ; point address
entry_address    macro    xx         ;this macro is used to generate
        dw    eline&xx&    ; the labels corresponding to the
        endm             ; inline code entry points
;
xx=2
    rept    20
    entry_address    %xx
xx=xx+2
    endm
;
cseg    ends
    end