Virtual Reality Zone/VRZONE.ISO/mac/PC/REND386/POLYBLIT/FTRIBLT.ASM

Assembly Source File | 1992-02-05 | 8KB | 415 lines

    TITLE    FASTRI - Fast triangle poly filling blitter
    NAME    FTRIBLT


    COMMENT    $

    Name:        FTRIBLT

        Written and (c) by Dave Stampe 9/11/91
        Not for commercial use, so get permission
        before marketing code using this stuff!
        For private PD use only.

        $

        .MODEL large

        .CODE
                ; big table more eff. than masking
                ; start byte lookup table
stmask:        REPT    40
        db    0ffh,07fh,03fh,01fh,00fh,007h,003h,001h
        ENDM
                ; end byte lookup table
fnmask:         REPT    40
        db      080h,0c0h,0e0h,0f0h,0f8h,0fch,0feh,0ffh
        ENDM

    extrn    _dpaddr        ; page base address

x1    equ    [bp+6]          ; arguments to _tpoly
y1    equ    [bp+8]
x2    equ    [bp+10]
y2    equ    [bp+12]
x3    equ    [bp+14]
y3     equ    [bp+16]


vline   equ    [bp-2]       ; video base addr. of line
lines    equ    [bp-4]        ; number of lines to fill
l_incr    equ    [bp-8]
r_incr    equ    [bp-12]

   ;
   ;   fastri(int x1,int y1, int x2, int y2, int x3, int y3)
   ;       vertices must be in CCW order!

        PUBLIC    _fastri

_fastri    proc    far

    .386
    push    bp
    mov    bp,sp
    sub    sp,16
    push    si
    push    di

    mov    eax,x1    ; consider as 32-bit hash: look for top, then left
    mov    ebx,x2
    mov    ecx,x3
    cmp    ebx,eax
    jae    nrot1
    xchg    eax,ebx    ; rotate till top-left is at head of list
    xchg    ebx,ecx
    cmp    ebx,eax
    jae    donerot
    xchg    eax,ebx
    xchg    ebx,ecx
    jmp    donerot

nrot1:    cmp    ecx,eax
    jae    donerot
    xchg    eax,ecx
    xchg    ebx,ecx

donerot:
    mov    x1,eax
    mov    x2,ebx
    mov    x3,ecx

    cld
    mov    ax,0a000h               ; set video segment
    mov    es,ax
    mov    al,y1
    mov    bl,40                   ; compute starting line adr
    mul    bl
    add    ax,WORD PTR ds:_dpaddr
    mov    vline,ax

    mov    ax,y1     ; determine config. of vertices: one of:
    cmp    ax,y3
    jz    flattop
    mov    ax,y2     ; 1  3      1      1      1
    cmp    ax,y3     ;                2          3
    jz    flatbot   ;  2      2  3     3     2
    jb    onleft
    jmp    onright

flatbot:
    movzx    ecx,word ptr y2       ; check for sliver poly
    sub    cx,y1
    jz    finished
    mov    lines,cx
    mov    ax,x2
    sub    ax,x1
    movsx    eax,ax      ; conv. to double prec. << 16
    je    roundpl1    ; zero slope
    cmp    cx,1
    je    roundpl1
    cdq
    shl    eax,16        ; (x2-x1)/(y2-y1)
    idiv    ecx
    cmp        eax,0       ; round up if pos (neg already rounded up)
    jle    roundpl1
    inc    eax
roundpl1:
    mov    l_incr,eax

    mov    ax,x3
    sub    ax,x1
    movsx    eax,ax      ; conv. to double prec. << 16
    je    roundpl2    ; zero slope
    cmp    cx,1
    je    roundpl2
    cdq
    shl    eax,16        ; (x2-x1)/(y2-y1)
    idiv    ecx
    cmp        eax,0       ; round up if pos (neg already rounded up)
    jle    roundpl2
    inc    eax
roundpl2:
    mov    r_incr,eax
    cmp    eax,l_incr
    jz    finished        ; sliver: don't bother

    mov    dx,x1            ; compute L,R start
    mov    cx,dx
    shl    edx,16
    mov    bx,cx
    mov    esi,edx
    add    edx,08000h             ; force left side to round up

    call    near ptr trapezoid
    jmp    finished

flattop:
    movzx    ecx,word ptr y2       ; check for sliver poly
    sub    cx,y1
    jz    finished
    mov    lines,cx
    mov    ax,x2
    sub    ax,x1
    movsx    eax,ax      ; conv. to double prec. << 16
    je    roundpl3    ; zero slope
    cmp    cx,1
    je    roundpl3    ; no slope needed if 1 line only
    cdq
    shl    eax,16        ; (x2-x1)/(y2-y1)
    idiv    ecx
    cmp        eax,0       ; round up if pos (neg already rounded up)
    jle    roundpl3
    inc    eax
roundpl3:
    mov    l_incr,eax

    mov    ax,x2
    sub    ax,x3
    movsx    eax,ax      ; conv. to double prec. << 16
    je    roundpl4    ; zero slope
    cmp    cx,1
    je    roundpl4    ; no slope needed if 1 line only
    cdq
    shl    eax,16        ; (x2-x1)/(y2-y1)
    idiv    ecx
    cmp        eax,0       ; round up if pos (neg already rounded up)
    jle    roundpl4
    inc    eax
roundpl4:
    mov    r_incr,eax
    cmp    eax,l_incr
    jz    finished        ; sliver: don't bother

    movzx    edx,word ptr x1             ; compute L,R start
    mov    bx,dx
    shl    edx,16
    add    edx,08000h             ; force left side to round up
    movzx    esi,word ptr x3
    mov    cx,si
    shl    esi,16

    call    near ptr trapezoid
    jmp    finished

onleft:
    movzx    ecx,word ptr y2       ; compute first slice height
    sub    cx,y1
    je    finished    ; sliver poly
    mov    lines,cx
    mov    ax,x2
    sub    ax,x1
    movsx    eax,ax      ; conv. to double prec. << 16
    je    roundpl5    ; zero slope
    cmp    cx,1
    je    roundpl5
    cdq
    shl    eax,16        ; (x2-x1)/(y2-y1)
    idiv    ecx
    cmp        eax,0       ; round up if pos (neg already rounded up)
    jle    roundpl5
    inc    eax
roundpl5:
    mov    l_incr,eax

    movzx    ecx,word ptr y3
    sub    cx,y1
    mov    ax,x3
    sub    ax,x1
    movsx    eax,ax      ; conv. to double prec. << 16
    je    roundpl6    ; zero slope
    cmp    cx,1
    je    roundpl6
    cdq
    shl    eax,16        ; (x2-x1)/(y2-y1)
    idiv    ecx
    cmp        eax,0       ; round up if pos (neg already rounded up)
    jle    roundpl6
    inc    eax
roundpl6:
    mov    r_incr,eax
    cmp    eax,l_incr
    jz    finished        ; sliver: don't bother

    mov    dx,x1            ; compute L,R start
    mov    cx,dx
    shl    edx,16
    mov    bx,cx
    mov    esi,edx
    add    edx,08000h             ; force left side to round up

    call    near ptr trapezoid
    push    esi        ; save full precison right side

    movzx    ecx,word ptr y3       ; compute second slice height
    sub    cx,y2
    mov    lines,cx
    mov    ax,x3
    sub    ax,x2
    movsx    eax,ax      ; conv. to double prec. << 16
    je    roundpl7    ; zero slope
    cmp    cx,1
    je    roundpl7
    cdq
    shl    eax,16        ; (x2-x1)/(y2-y1)
    idiv    ecx
    cmp        eax,0       ; round up if pos (neg already rounded up)
    jle    roundpl7
    inc    eax
roundpl7:
    mov    l_incr,eax   ; change left increment

    pop    esi
    mov    ecx,esi         ; restore right side
    shr    ecx,16

    movzx    edx,word ptr x2             ; compute L start
    mov    bx,dx
    shl    edx,16
    add    edx,08000h        ; force left side to round up

    call    near ptr trapezoid
    jmp    finished

onright:
    movzx    ecx,word ptr y2       ; compute first slice height
    sub    cx,y1
    je    finished
    mov    ax,x2
    sub    ax,x1
    movsx    eax,ax      ; conv. to double prec. << 16
    je    roundpl8    ; zero slope
    cmp    cx,1
    je    roundpl8
    cdq
    shl    eax,16        ; (x2-x1)/(y2-y1)
    idiv    ecx
    cmp        eax,0       ; round up if pos (neg already rounded up)
    jle    roundpl8
    inc    eax
roundpl8:
    mov    l_incr,eax

    movzx    ecx,word ptr y3       ; compute first slice height
    sub    cx,y1
    mov    lines,cx
    mov    ax,x3
    sub    ax,x1
    movsx    eax,ax      ; conv. to double prec. << 16
    je    roundpl9    ; zero slope
    cmp    cx,1
    je    roundpl9
    cdq
    shl    eax,16        ; (x2-x1)/(y2-y1)
    idiv    ecx
    cmp        eax,0       ; round up if pos (neg already rounded up)
    jle    roundpl9
    inc    eax
roundpl9:
    mov    r_incr,eax
    cmp    eax,l_incr
    jz    finished        ; sliver: don't bother

    mov    dx,x1           ; compute L,R start
    mov    cx,dx
    shl    edx,16
    mov    bx,cx
    mov    esi,edx
    add    edx,08000h             ; force left side to round up

    call    near ptr trapezoid
    push    edx        ; save full precison left side

    movzx    ecx,word ptr y2       ; compute second slice height
    sub    cx,y3
    mov    lines,cx
    mov    ax,x2
    sub    ax,x3
    movsx    eax,ax      ; conv. to double prec. << 16
    je    roundpla    ; zero slope
    cmp    cx,1
    je    roundpla
    cdq
    shl    eax,16        ; (x2-x1)/(y2-y1)
    idiv    ecx
    cmp        eax,0       ; round up if pos (neg already rounded up)
    jle    roundpla
    inc    eax
roundpla:
    mov    r_incr,eax   ; change left increment

    pop    edx
    mov    ebx,edx         ; restore left side
    shr    ebx,16

    movzx    esi,word ptr x3             ; compute R start
    mov    cx,si
    shl    esi,16

    call    near ptr trapezoid
    jmp    finished


finished:
    pop    di                         ; exit code
    pop    si
    mov    sp,bp
    pop    bp
    ret

_fastri    endp



trapezoid:    ; call with  bx = left, cx = right
        ; edx = (left+0.5)>>16, esi = right<<16
        ; vline, lines, l_incr, r_incr all set up

nextline:
        ; start of fast h line blitter:
        ;  bx=left side, cx=right side, vline=line start

    mov    al,BYTE PTR cs:[bx+stmask]  ; left mask
    shr    bx,3                        ; left address

    mov    di,cx
    mov    ah,BYTE PTR cs:[di+fnmask]  ; right mask
    shr    cx,3                        ; right address

    mov    di,vline            ; start address
    add    di,bx
    sub    cx,bx                       ; number of bytes-1
    je    short onebyte
    jc    short doneline              ; clip trap

    and    es:[di],al                  ; mask first byte
    inc    di
    dec    cx                          ; mask rest
    mov    al,0ffh                     ; rep faster than test and jmp
    rep    stosb                       ; for zero byte case
    and    es:[di],ah                  ; mask last byte
    jmp    short doneline

onebyte:
    and    al,ah
    and    es:[di],al        ; single byte mask

doneline:
    mov    ax,40                   ; next line address
    add    vline,ax

    add    edx,DWORD PTR l_incr    ; step left, right edges
    add    esi,DWORD PTR r_incr
    mov    ebx,edx            ; convert fixed pt to integer
    sar    ebx,16
    mov    ecx,esi
    sar    ecx,16

    dec    WORD PTR lines          ; done lines?
    jg    short nextline

donetri:                                ; finished all drawing
exit:
    retn

    end