leptonica write to memory with PNG format

insert to leptonica -> pngio.c
//-------------------------------------------------------------------------------
struct mem_encode
{
  char *buffer;
  size_t size;
};


void
my_png_write_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
  /* with libpng15 next line causes pointer deference error; use libpng12 */
  struct mem_encode* p=(struct mem_encode*)png_ptr->io_ptr;
  size_t nsize = p->size + length;

  /* allocate or grow buffer */
  if(p->buffer)
    p->buffer = (char *)realloc(p->buffer, nsize);
  else
    p->buffer = (char *)malloc(nsize);

  if(!p->buffer)
    png_error(png_ptr, "Write Error");

  /* copy new bytes to end of buffer */
  memcpy(p->buffer + p->size, data, length);
  p->size += length;
}

void
my_png_flush(png_structp png_ptr)
{
}
//------------------------------------------------------------------------------------------

change "pixWriteMemPng"  function in leptonica -> pngio.c
//------------------------------------------------------------------------------------------
l_int32
pixWriteMemPng(l_uint8  **pdata,
               size_t    *psize,
               PIX       *pix,
               l_float32  gamma)
{
struct mem_encode state;
char         commentstring[] = "Comment";
l_int32      i, j, k;
l_int32      wpl, d, cmflag;
l_int32      ncolors;
l_int32     *rmap, *gmap, *bmap;
l_uint32    *data, *ppixel;
png_byte     bit_depth, color_type;
png_uint_32  w, h;
png_uint_32  xres, yres;
png_bytep   *row_pointers;
png_bytep    rowbuffer;
png_structp  png_ptr;
png_infop    info_ptr;
png_colorp   palette;
PIX         *pixt;
PIXCMAP     *cmap;
char        *text;

    PROCNAME("pixWriteMemPng");
    if (!pix)
        return ERROR_INT("pix not defined", procName, 1);

        /* Allocate the 2 data structures */
    if ((png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING,
                   (png_voidp)NULL, NULL, NULL)) == NULL)
        return ERROR_INT("png_ptr not made", procName, 1);

    if ((info_ptr = png_create_info_struct(png_ptr)) == NULL) {
        png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
        return ERROR_INT("info_ptr not made", procName, 1);
    }

        /* Set up png setjmp error handling */
    if (setjmp(png_jmpbuf(png_ptr))) {
        png_destroy_write_struct(&png_ptr, &info_ptr);
        return ERROR_INT("internal png error", procName, 1);
    }
    state.buffer = NULL;
    state.size = 0;

   png_set_write_fn(png_ptr, &state, my_png_write_data, my_png_flush);

        /* With best zlib compression (9), get between 1 and 10% improvement
         * over default (5), but the compression is 3 to 10 times slower.
         * Our default compression is the zlib default (5). */
    png_set_compression_level(png_ptr, var_ZLIB_COMPRESSION);

    w = pixGetWidth(pix);
    h = pixGetHeight(pix);
    d = pixGetDepth(pix);
    if ((cmap = pixGetColormap(pix)))
        cmflag = 1;
    else
        cmflag = 0;

        /* Set the color type and bit depth. */
    if (d == 32 && var_PNG_WRITE_ALPHA == 1) {
        bit_depth = 8;
        color_type = PNG_COLOR_TYPE_RGBA;   /* 6 */
        cmflag = 0;  /* ignore if it exists */
    }
    else if (d == 24 || d == 32) {
        bit_depth = 8;
        color_type = PNG_COLOR_TYPE_RGB;   /* 2 */
        cmflag = 0;  /* ignore if it exists */
    }
    else {
        bit_depth = d;
        color_type = PNG_COLOR_TYPE_GRAY;  /* 0 */
    }
    if (cmflag)
        color_type = PNG_COLOR_TYPE_PALETTE;  /* 3 */

#if  DEBUG
    fprintf(stderr, "cmflag = %d, bit_depth = %d, color_type = %d\n",
            cmflag, bit_depth, color_type);
#endif  /* DEBUG */

    png_set_IHDR(png_ptr, info_ptr, w, h, bit_depth, color_type,
                 PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE,
                 PNG_FILTER_TYPE_BASE);

        /* Store resolution in ppm, if known */
    xres = (png_uint_32)(39.37 * (l_float32)pixGetXRes(pix) + 0.5);
    yres = (png_uint_32)(39.37 * (l_float32)pixGetYRes(pix) + 0.5);
    if ((xres == 0) || (yres == 0))
        png_set_pHYs(png_ptr, info_ptr, 0, 0, PNG_RESOLUTION_UNKNOWN);
    else
        png_set_pHYs(png_ptr, info_ptr, xres, yres, PNG_RESOLUTION_METER);

    if (cmflag) {
        pixcmapToArrays(cmap, &rmap, &gmap, &bmap);
        ncolors = pixcmapGetCount(cmap);

            /* Make and save the palette */
        if ((palette = (png_colorp)(CALLOC(ncolors, sizeof(png_color))))
                == NULL)
            return ERROR_INT("palette not made", procName, 1);

        for (i = 0; i < ncolors; i++) {
            palette.red = (png_byte)rmap;
            palette.green = (png_byte)gmap;
            palette.blue = (png_byte)bmap;
        }

        png_set_PLTE(png_ptr, info_ptr, palette, (int)ncolors);
        FREE(rmap);
        FREE(gmap);
        FREE(bmap);
    }

        /* 0.4545 is treated as the default by some image
         * display programs (not gqview).  A value > 0.4545 will
         * lighten an image as displayed by xv, display, etc. */
    if (gamma > 0.0)
        png_set_gAMA(png_ptr, info_ptr, (l_float64)gamma);

    if ((text = pixGetText(pix))) {
        png_text text_chunk;
        text_chunk.compression = PNG_TEXT_COMPRESSION_NONE;
        text_chunk.key = commentstring;
        text_chunk.text = text;
        text_chunk.text_length = strlen(text);
#ifdef PNG_ITXT_SUPPORTED
        text_chunk.itxt_length = 0;
        text_chunk.lang = NULL;
        text_chunk.lang_key = NULL;
#endif
        png_set_text(png_ptr, info_ptr, &text_chunk, 1);
    }

        /* Write header and palette info */
    png_write_info(png_ptr, info_ptr);

    if ((d != 32) && (d != 24))
    {  /* not rgb color */
            /* Generate a temporary pix with bytes swapped.
             * For a binary image, there are two conditions in
             * which you must first invert the data for writing png:
             *    (a) no colormap
             *    (b) colormap with BLACK set to 0
             * png writes binary with BLACK = 0, unless contradicted
             * by a colormap.  If the colormap has BLACK = "1"
             * (typ. about 255), do not invert the data.  If there
             * is no colormap, you must invert the data to store
             * in default BLACK = 0 state.  */
        if (d == 1 &&
            (!cmap || (cmap && ((l_uint8 *)(cmap->array))[0] == 0x0))) {
            pixt = pixInvert(NULL, pix);
            pixEndianByteSwap(pixt);
        }
        else
            pixt = pixEndianByteSwapNew(pix);
        if (!pixt) {
            png_destroy_write_struct(&png_ptr, &info_ptr);
            return ERROR_INT("pixt not made", procName, 1);
        }

            /* Make and assign array of image row pointers */
        if ((row_pointers = (png_bytep *)CALLOC(h, sizeof(png_bytep))) == NULL)
            return ERROR_INT("row-pointers not made", procName, 1);
        wpl = pixGetWpl(pixt);
        data = pixGetData(pixt);
        for (i = 0; i < h; i++)
            row_pointers = (png_bytep)(data + i * wpl);
        png_set_rows(png_ptr, info_ptr, row_pointers);

            /* Transfer the data */
        png_write_image(png_ptr, row_pointers);
        png_write_end(png_ptr, info_ptr);

        if (cmflag)
            FREE(palette);
        FREE(row_pointers);
        pixDestroy(&pixt);
        png_destroy_write_struct(&png_ptr, &info_ptr);
        *pdata=(unsigned char *)state.buffer;
        *psize=state.size;
        return 0;
    }

        /* For rgb, compose and write a row at a time */
    data = pixGetData(pix);
    wpl = pixGetWpl(pix);
    if (d == 24) {  /* See note 7 above: special case of 24 bpp rgb */
        for (i = 0; i < h; i++) {
            ppixel = data + i * wpl;
            png_write_rows(png_ptr, (png_bytepp)&ppixel, 1);
        }
    }
    else {  /* 32 bpp rgb and rgba */
        if ((rowbuffer = (png_bytep)CALLOC(w, 4)) == NULL)
            return ERROR_INT("rowbuffer not made", procName, 1);
        for (i = 0; i < h; i++) {
            ppixel = data + i * wpl;
            for (j = k = 0; j < w; j++) {
                rowbuffer[k++] = GET_DATA_BYTE(ppixel, COLOR_RED);
                rowbuffer[k++] = GET_DATA_BYTE(ppixel, COLOR_GREEN);
                rowbuffer[k++] = GET_DATA_BYTE(ppixel, COLOR_BLUE);
                if (var_PNG_WRITE_ALPHA == 1)
                    rowbuffer[k++] = GET_DATA_BYTE(ppixel, L_ALPHA_CHANNEL);
                ppixel++;
            }

            png_write_rows(png_ptr, &rowbuffer, 1);
        }
        FREE(rowbuffer);
    }

    png_write_end(png_ptr, info_ptr);

    if (cmflag)
        FREE(palette);
    png_destroy_write_struct(&png_ptr, &info_ptr);
    *pdata=(unsigned char *)state.buffer;
    *psize=state.size;
    return 0;
}

TEST
//----------------------------------------------------------------------------------------------------

    unsigned char* dstTmp = NULL;
    FILE *file;
    file =fopen("d:/b.bmp","rb");
    fseek (file , 0 , SEEK_END);
    size_t length=ftell (file);
    rewind (file);
    dstTmp = (unsigned char*) malloc (sizeof(unsigned char)*length);
    fread (dstTmp,1,length,file);
    fclose(file);

    Pix *pix = pixReadMem(dstTmp,length);
   
    pixWriteMemPng(&dstTmp,&length,pix,0);

    file=fopen("d:/test.png","wb");
    fwrite(dstTmp,1,length,file);
    fclose(file);
//----------------------------------------------------------------------------------------------------