Tech Arsenal 1/Tech Arsenal (Arsenal Computer).ISO/tek-04/xlib03.zip/XLINE.ASM

Assembly Source File | 1993-04-05 | 5KB | 320 lines

;-----------------------------------------------------------------------
; MODULE XLINE
;
; Line drawing functions.
;
; Compile with Tasm.
; C callable.
;
;
; ****** XLIB - Mode X graphics library                ****************
; ******                                               ****************
; ****** Written By Themie Gouthas                     ****************
; ****** Aeronautical Research Laboratory              ****************
; ****** Defence Science and Technology Organisation   ****************
; ****** Australia                                     ****************
;
; [e-mail]
; [e-mail]
;-----------------------------------------------------------------------
include xlib.inc
include xline.inc

    .code


ModeXAddr       macro
    mov    cl,bl
    push    dx
    mov    dx,[_ScrnLogicalByteWidth]
    mul    dx
    pop    dx
    shr    bx,2
    add    bx,ax
    add     bx,[PgOffs]
    and    cl,3
    endm


;-----------------------------------------------------------------------
; _x_line
;
; Line drawing function for all MODE X 256 Color resolutions
; Based on code from "PC and PS/2 Video Systems" by Richard Wilton.
;
; Compile with Tasm.
; C callable.
;

_x_line     proc
ARG     x1:word,y1:word,x2:word,y2:word,Color:word,PgOffs:word
LOCAL   vertincr:word,incr1:word,incr2:word,routine:word=LocalStk
    push    bp        ; Set up stack frame
    mov    bp,sp
    sub    sp,LocalStk
    push    si
    push    di

    mov    ax,0a000h
    mov    es,ax

    mov    dx,SC_INDEX    ; setup for plane mask access

; check for vertical line

    mov    si,[_ScrnLogicalByteWidth]
    mov    cx,[x2]
    sub    cx,[x1]
    jz    VertLine

; force x1 < x2

    jns    L01

    neg    cx

    mov    bx,[x2]
    xchg    bx,[x1]
    mov    [x2],bx

    mov    bx,[y2]
    xchg    bx,[y1]
    mov    [y2],bx

; calc dy = abs(y2 - y1)

L01:
    mov    bx,[y2]
    sub    bx,[y1]
    jnz    short skip
    jmp     HorizLine
skip:        jns    L03

    neg    bx
    neg    si

; select appropriate routine for slope of line

L03:
    mov    [vertincr],si
    mov    [routine],offset LoSlopeLine
    cmp    bx,cx
    jle    L04
    mov    [routine],offset HiSlopeLine
    xchg    bx,cx

; calc initial decision variable and increments

L04:
    shl    bx,1
    mov    [incr1],bx
    sub    bx,cx
    mov    si,bx
    sub    bx,cx
    mov    [incr2],bx

; calc first pixel address

    push    cx
    mov    ax,[y1]
    mov    bx,[x1]
    ModeXAddr
    mov    di,bx
    mov    al,1
    shl    al,cl
    mov    ah,al        ; duplicate nybble
    shl    al,4
    add    ah,al
    mov    bl,ah
    pop    cx
    inc    cx
    jmp    [routine]

; routine for verticle lines

VertLine:
    mov    ax,[y1]
    mov    bx,[y2]
    mov    cx,bx
    sub    cx,ax
    jge    L31
    neg    cx
    mov    ax,bx

L31:
    inc    cx
    mov    bx,[x1]
    push    cx
    ModeXAddr

    mov    ah,1
    shl    ah,cl
    mov    al,MAP_MASK
    out    dx,ax
    pop    cx
    mov    ax, word ptr [Color]

; draw the line

L32:
    mov    es:[bx],al
    add    bx,si
    loop    L32
    jmp    Lexit

; routine for horizontal line

HorizLine:
    push    ds

    mov    ax,[y1]
    mov    bx,[x1]
    ModeXAddr

    mov    di,bx     ; set dl = first byte mask
    mov    dl,00fh
    shl    dl,cl

    mov    cx,[x2] ; set dh = last byte mask
    and    cl,3
    mov    dh,00eh
    shl    dh,cl
    not    dh

; determine byte offset of first and last pixel in line

    mov    ax,[x2]
    mov    bx,[x1]

    shr    ax,2     ; set ax = last byte column
    shr    bx,2    ; set bx = first byte column
    mov    cx,ax    ; cx = ax - bx
    sub    cx,bx

    mov    ax,dx    ; mov end byte masks to ax
    mov    dx,SC_INDEX ; setup dx for VGA outs
    mov     bx, [Color]

; set pixels in leftmost byte of line

    or    cx,cx      ; is start and end pt in same byte
    jnz    L42        ; no !
    and    ah,al      ; combine start and end masks
    jmp    short L44

L42:            push    ax
    mov     ah,al
    mov     al,MAP_MASK
    out     dx,ax
    mov    al,bl
    stosb
    dec    cx

; draw remainder of the line

L43:
    mov    ah,0Fh
    mov    al,MAP_MASK
    out    dx,ax
    mov    al,bl
    rep    stosb
    pop     ax

; set pixels in rightmost byte of line

L44:
    mov    al,MAP_MASK
    out    dx, ax
    mov     byte ptr es:[di],bl
    pop    ds
    jmp    short Lexit


; routine for dy >= dx (slope <= 1)

LoSlopeLine:
    mov    al,MAP_MASK
    mov    bh,byte ptr [Color]
L10:
    mov    ah,bl

L11:
    or    ah,bl
    rol    bl,1
    jc    L14

; bit mask not shifted out

    or    si,si
    jns    L12
    add    si,[incr1]
    loop    L11

    out    dx,ax
    mov    es:[di],bh
    jmp    short Lexit

L12:
    add    si,[incr2]
    out    dx,ax
    mov    es:[di],bh
    add    di,[vertincr]
    loop    L10
    jmp    short Lexit

; bit mask shifted out

L14:            out    dx,ax
    mov    es:[di],bh
    inc    di
    or    si,si
    jns    L15
    add    si,[incr1]
    loop    L10
    jmp    short Lexit

L15:
    add    si,[incr2]
    add    di,[vertincr]
    loop    L10
    jmp    short Lexit

; routine for dy > dx (slope > 1)

HiSlopeLine:
    mov    bx,[vertincr]
    mov    al,MAP_MASK
L21:            out    dx,ax
    push    ax
    mov    ax,[Color]
    mov    es:[di],al
    pop    ax
    add    di,bx

L22:
    or    si,si
    jns    L23

    add    si,[incr1]
    loop    L21
    jmp    short Lexit

L23:
    add    si,[incr2]
    rol    ah,1
    adc    di,0
lx21:    loop    L21

; return to caller

Lexit:
    pop    di
    pop    si
    mov    sp,bp
    pop    bp
    ret

_x_line    endp

end