The following code from EDDHBBLT.ASM is similar to code found throughout the driver.

; ss:esp now points to the destination coordinates:
  pop these straight into
; the hardware
        pop     eax
        memregwrite     dest_map, eax

; write the pixel op to kick off the blt
        memregwrite     pixel_op, edx

IFDEF HARD_DRAW

; see if the source is vram or not by checking vram marker
        IFDEF   _8514
        push    ebx
        mov     ebx, AIxfer.pbmhSrc
        mov     eax, [ebx].bit map_address
        and     eax, 0f0000000h
        cmp     eax, 0f0000000h
        pop     ebx
        jz      short @f
        call    SoftSrcSpecialist
        jmp     short soft_done

@@:     call    SrcSpecialist

soft_done:
        ENDIF   ;_8514

ELSE

        saveregs
        call    _eddf_MESS
        restoreregs

ENDIF

The following code from EDDHLNE.ASM shows the procedure for Soft-Draw mode. In this code, setup is created and calls eddf_MESS.

ELSE ;SOFT_DRAW

IFDEF _8514

        mov             eax,_SPad.ptsNewStart
        memregwrite     dest_map,eax

        mov             ax,_SPad.sK1
        memregwrite     sr_K1,ax

        mov             ax,_SPad.sK2
        memregwrite     sr_K2,ax

        mov             ax,_SPad.usErrorTerm
        memregwrite     Err_Term,ax

        mov             ax,_SPad.usMajorAxis
        memregwrite     dim1,ax

ENDIF ;_8514

        saveregs
        call    _eddf_MESS
        restoreregs
ENDIF

The S3 driver draws to bit maps by having eddf_MESS emulate certain XGA operations in software. The eddf_MESS routine interprets the Shadow8514Regs, based on the parameters therein, and the pel operation, then calls one of a number of routines to perform the requested drawing operation. For the most part, eddf_MESS is a collection of jump tables to routines that do the work. Each case and each pel depth are broken out into special cased routines. To some extent, this explains the size of the code. Individually, the routines themselves are not complex, although many of them are implemented as macros. The following is a list of the files that comprise the MESS, and the functions they perform.