gondwana.ecr.mu.oz.au/pub//Graphics.tar/Graphics/VOGLE.ZIP/VOGLE/DRIVERS/IBMPC/EGALINE.ASM

Assembly Source File | 2000-02-11 | 5KB | 345 lines

    TITLE    EGALINE - Fast line drawing routine.
    NAME    EGALINE
    PAGE    55,132


    COMMENT    $

    Name:        EGALINE

    Function:    Draw a line in the following EGA/VGA graphics modes:
            200 line 16 colour modes
            350 line modes
            640 x 480 16 colour modes

    Caller:        Microsoft C:

            void     egaline(x1, y1, x2, y2, n);
                int    x1, y1, x2, y2;    /* pixel co-ords */
                int    n;        /* pixel value */
        $


; Stack frame addressing - LARGE CODE MODEL

ARGx1        EQU    word ptr [bp+6]
ARGy1        EQU    word ptr [bp+8]
ARGx2        EQU    word ptr [bp+10]
ARGy2        EQU    word ptr [bp+12]
ARGn        EQU    byte ptr [bp+14]

VARvertincr    EQU    word ptr [bp-6]
VARincr1    EQU    word ptr [bp-8]
VARincr2    EQU    word ptr [bp-10]
VARroutine    EQU    word ptr [bp-12]

ByteOffsetShift    EQU    3
BytesPerLine    EQU    80
RMWbits        EQU    0


VEGA_TEXT    SEGMENT    byte public 'CODE'
        ASSUME    cs:VEGA_TEXT

        EXTRN    egapaddr:far
        PUBLIC    _egaline

_egaline    PROC    far

        push    bp        ; Set up stack frame
        mov    bp,sp
        sub    sp,10
        push    si
        push    di

; config graphics controller

        mov    dx,3CEH
        mov    ah,ARGn
        xor    al,al
        out    dx,ax

        mov    ax,0F01H
        out    dx,ax

        mov    ah,RMWbits
        mov    al,3
        out    dx,ax

; check for vertical line

        mov    si,BytesPerLine
        mov    cx,ARGx2
        sub    cx,ARGx1
        jz    VertLine

; force x1 < x2

        jns    L01

        neg    cx

        mov    bx,ARGx2
        xchg    bx,ARGx1
        mov    ARGx2,bx

        mov    bx,ARGy2
        xchg    bx,ARGy1
        mov    ARGy2,bx

; calc dy = abs(y2 - y1)

L01:
        mov    bx,ARGy2
        sub    bx,ARGy1
        jz    HorizLine
        jns    L03

        neg    bx
        neg    si

; select appropriate routine for slope of line

L03:
        mov    VARvertincr,si
        mov    VARroutine,offset LoSlopeLine
        cmp    bx,cx
        jle    L04
        mov    VARroutine,offset HiSlopeLine
        xchg    bx,cx

; calc initial decision variable and increments

L04:
        shl    bx,1
        mov    VARincr1,bx
        sub    bx,cx
        mov    si,bx
        sub    bx,cx
        mov    VARincr2,bx

; calc first pixel address

        push    cx
        mov    ax,ARGy1
        mov    bx,ARGx1
        call    egapaddr
        mov    di,bx
        shl    ah,cl
        mov    bl,ah
        mov    al,8
        pop    cx
        inc    cx
        jmp    VARroutine

; routine for verticle lines

VertLine:
        mov    ax,ARGy1
        mov    bx,ARGy2
        mov    cx,bx
        sub    cx,ax
        jge    L31
        neg    cx
        mov    ax,bx

L31:
        inc    cx
        mov    bx,ARGx1
        push    cx
        call    egapaddr

; set up graphics controller

        shl    ah,cl
        mov    al,8
        out    dx,ax
        pop    cx

; draw the line

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

; routine for horizontal line

HorizLine:
        push    ds

        mov    ax,ARGy1
        mov    bx,ARGx1
        call    egapaddr
        mov    di,bx
        mov    dh,ah
        not    dh
        shl    dh,cl
        not    dh

        mov    cx,ARGx2
        and    cl,7
        xor    cl,7
        mov    dl,0FFH
        shl    dl,cl

; determine byte offset of first and last pixel in line

        mov    ax,ARGx2
        mov    bx,ARGx1
        mov    cl,ByteOffsetShift

        shr    ax,cl
        shr    bx,cl
        mov    cx,ax
        sub    cx,bx

; get graphics controller port address into DX

        mov    bx,dx
        mov    dx,3CEH
        mov    al,8

; make video buffer addressable through DS:SI

        push    es
        pop    ds
        mov    si,di

; set pixels in leftmost byte of line

        or    bh,bh
        js    L43
        or    cx,cx
        jnz    L42
        and    bl,bh
        jmp    short L44

L42:
        mov    ah,bh
        out    dx,ax
        movsb
        dec    cx

; draw remainder of the line

L43:
        mov    ah,0FFH
        out    dx,ax
        rep    movsb

; set pixels in rightmost byte of line

L44:
        mov    ah,bl
        out    dx,ax
        movsb
        pop    ds
        jmp    short Lexit



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

LoSlopeLine:

L10:
        mov    ah,bl

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

; bit mask not shifted out

        or    si,si
        jns    L12
        add    si,VARincr1
        loop    L11

        out    dx,ax
        or    es:[di],al
        jmp    short Lexit

L12:
        add    si,VARincr2
        out    dx,ax
        or    es:[di],al
        add    di,VARvertincr
        loop    L10
        jmp    short Lexit

; bit mask shifted out

L14:
        out    dx,ax
        or    es:[di],al
        inc    di
        or    si,si
        jns    L15
        add    si,VARincr1
        loop    L10
        jmp    short Lexit

L15:
        add    si,VARincr2
        add    di,VARvertincr
        loop    L10
        jmp    short Lexit



; routine for dy > dx (slope > 1)

HiSlopeLine:
        mov    bx,VARvertincr

L21:
        out    dx,ax
        or    es:[di],al
        add    di,bx

L22:
        or    si,si
        jns    L23

        add    si,VARincr1
        loop    L21
        jmp    short Lexit

L23:
        add    si,VARincr2
        ror    ah,1
        adc    di,0
        loop    L21

; restore default graphics controoler state and return to caller

Lexit:

COMMENT $
        xor    ax,ax
        out    dx,ax
        inc    ax
        out    dx,ax
        mov    ax,3
        out    dx,ax
        mov    ax,0FF08H
        out    dx,ax
        $

        pop    di
        pop    si
        mov    sp,bp
        pop    bp
        ret

_egaline    endp

VEGA_TEXT    ends

        end