Assembly code snippets

Details

Title	Resampling 1/2x
Author	Thomas
Submitted by:	Thomas
Date added:	2002-02-17 16:33:29
Date modified:	2002-02-17 16:33:29

Comments

This snippet rescales bitmap data (32-bits per pixel) into a bitmap of half the size.
lpSrc is a pointer to the source bitmap data
lpDest is a pointer for the output data
dwWidth is the width of the source bitmap
dwHeight is the height of the source bitmap.
It resamples the bitmap which means it calculates one output pixel by averaging four input pixels. The algorithm uses MMX, the width should be a multiple of 4, height should be a multiple of 2.

Snippet

Resample proc uses edi esi ebx lpSrc:DWORD, lpDest:DWORD, dwWidth:DWORD, dwHeight:DWORD
    mov     esi, lpSrc
    mov     edi, lpDest
    mov     edx, dwWidth
    shr     edx, 1

    mov     ecx, dwWidth

    pxor    MM4, MM4

    mov     ebx, dwHeight
    shr     ebx, 1
    ALIGN 16
    @nextline:

        mov     edx, ecx
        shr     edx, 2
        ALIGN 16
        @nextpixel:
            movq        MM0, [esi]          ; MM0: X2 R2 G2 B2-X1 R1 G1 B1
            movq        MM1, [esi+8]        ; MM1: X4 R4 G4 B4-X3 R3 G3 B3
            movq        MM2, [esi+4*ecx]        ; MM2: X6 R6 G6 B6-X5 R5 G5 B5
            movq        MM3, [esi+4*ecx+8]  ; MM3: X8 R8 G8 B8-X7 R7 G7 B7

            movq        MM5, MM0
            movq        MM6, MM2

            punpckhbw   MM0, MM4            ; MM0: 00 X2 00 R2-00 G2 00 B2
            punpckhbw   MM2, MM4            ; MM2: 00 X6 00 R6-00 B6 00 B6
            punpcklbw   MM5, MM4            ; MM5: 00 X1 00 R1-00 G1 00 B1
            punpcklbw   MM6, MM4            ; MM6: 00 X5 00 R5-00 G5 00 B5

            paddw       MM0, MM2
            paddw       MM0, MM5
            paddw       MM0, MM6
            psrlw       MM0, 2

            ; second pixel:

            movq        MM5, MM1
            movq        MM6, MM3

            punpckhbw   MM1, MM4            ; MM1: 00 X4 00 R4-00 G4 00 B4
            punpckhbw   MM3, MM4            ; MM3: 00 X8 00 R8-00 B8 00 B8
            punpcklbw   MM5, MM4            ; MM5: 00 X3 00 R3-00 G3 00 B3
            punpcklbw   MM6, MM4            ; MM6: 00 X7 00 R7-00 G7 00 B7

            paddw       MM1, MM3
            paddw       MM1, MM5
            paddw       MM1, MM6
            psrlw       MM1, 2

            ; now:  MM0: 00 XQ 00 RQ-00 GQ 00 BQ ;where Q is the first mixed pixel
            ; now:  MM1: 00 XP 00 RP-00 GP 00 BP ;where P is the second mixed pixel
            ; output should be: BQ GQ RQ XQ-BP GP RP XP (in mem)
            ;                   XP RP GP BP XQ RQ GQ BQ (in reg)

            packuswb    MM0, MM1
            movq        [edi], MM0

            add     esi, 16
            add     edi, 8
            dec     edx
            jnz     @nextpixel

        lea     esi, [esi+4*ecx]
        dec     ebx
        jnz     @nextline
    emms
ret
Resample endp