if ((bg[pat].type & 0x07) == 0) {        uch r1_min  = rgb[bg[pat].rgb1_min].r;        uch g1_min  = rgb[bg[pat].rgb1_min].g;        uch b1_min  = rgb[bg[pat].rgb1_min].b;        uch r2_min  = rgb[bg[pat].rgb2_min].r;        uch g2_min  = rgb[bg[pat].rgb2_min].g;        uch b2_min  = rgb[bg[pat].rgb2_min].b;        int r1_diff = rgb[bg[pat].rgb1_max].r - r1_min;        int g1_diff = rgb[bg[pat].rgb1_max].g - g1_min;        int b1_diff = rgb[bg[pat].rgb1_max].b - b1_min;        int r2_diff = rgb[bg[pat].rgb2_max].r - r2_min;        int g2_diff = rgb[bg[pat].rgb2_max].g - g2_min;        int b2_diff = rgb[bg[pat].rgb2_max].b - b2_min;        for (row = 0;  row < rpng2_info.height;  ++row) {            yidx = row % bgscale;            even_odd_vert = (row / bgscale) & 1;            r1 = r1_min + (r1_diff * yidx) / yidx_max;            g1 = g1_min + (g1_diff * yidx) / yidx_max;            b1 = b1_min + (b1_diff * yidx) / yidx_max;            r1_inv = r1_min + (r1_diff * (yidx_max-yidx)) / yidx_max;            g1_inv = g1_min + (g1_diff * (yidx_max-yidx)) / yidx_max;            b1_inv = b1_min + (b1_diff * (yidx_max-yidx)) / yidx_max;            r2 = r2_min + (r2_diff * yidx) / yidx_max;            g2 = g2_min + (g2_diff * yidx) / yidx_max;            b2 = b2_min + (b2_diff * yidx) / yidx_max;            r2_inv = r2_min + (r2_diff * (yidx_max-yidx)) / yidx_max;            g2_inv = g2_min + (g2_diff * (yidx_max-yidx)) / yidx_max;            b2_inv = b2_min + (b2_diff * (yidx_max-yidx)) / yidx_max;            dest = bg_data + row*bg_rowbytes;            for (i = 0;  i < rpng2_info.width;  ++i) {                even_odd_horiz = (i / bgscale) & 1;                even_odd = even_odd_vert ^ even_odd_horiz;                invert_column =                  (even_odd_horiz && (bg[pat].type & 0x10));                if (even_odd == 0) {         /* gradient #1 */                    if (invert_column) {                        *dest++ = r1_inv;                        *dest++ = g1_inv;                        *dest++ = b1_inv;                    } else {                        *dest++ = r1;                        *dest++ = g1;                        *dest++ = b1;                    }                } else {                     /* gradient #2 */                    if ((invert_column && invert_gradient2) ||                        (!invert_column && !invert_gradient2))                    {                        *dest++ = r2;        /* not inverted or */                        *dest++ = g2;        /*  doubly inverted */                        *dest++ = b2;                    } else {                        *dest++ = r2_inv;                        *dest++ = g2_inv;    /* singly inverted */                        *dest++ = b2_inv;                    }                }            }        }/*---------------------------------------------------------------------------    Soft gradient-diamonds with scale = bgscale.  Code contributed by Adam    M. Costello.  ---------------------------------------------------------------------------*/    } else if ((bg[pat].type & 0x07) == 1) {        hmax = (bgscale-1)/2;   /* half the max weight of a color */        max = 2*hmax;           /* the max weight of a color */        r1 = rgb[bg[pat].rgb1_max].r;        g1 = rgb[bg[pat].rgb1_max].g;        b1 = rgb[bg[pat].rgb1_max].b;        r2 = rgb[bg[pat].rgb2_max].r;        g2 = rgb[bg[pat].rgb2_max].g;        b2 = rgb[bg[pat].rgb2_max].b;        for (row = 0;  row < rpng2_info.height;  ++row) {            yidx = row % bgscale;            if (yidx > hmax)                yidx = bgscale-1 - yidx;            dest = bg_data + row*bg_rowbytes;            for (i = 0;  i < rpng2_info.width;  ++i) {                xidx = i % bgscale;                if (xidx > hmax)                    xidx = bgscale-1 - xidx;                k = xidx + yidx;                *dest++ = (k*r1 + (max-k)*r2) / max;                *dest++ = (k*g1 + (max-k)*g2) / max;                *dest++ = (k*b1 + (max-k)*b2) / max;            }        }/*---------------------------------------------------------------------------    Radial "starburst" with azimuthal sinusoids; [eventually number of sinu-    soids will equal bgscale?].  This one is slow but very cool.  Code con-    tributed by Pieter S. van der Meulen (originally in Smalltalk).  ---------------------------------------------------------------------------*/    } else if ((bg[pat].type & 0x07) == 2) {        uch ch;        int ii, x, y, hw, hh, grayspot;        double freq, rotate, saturate, gray, intensity;        double angle=0.0, aoffset=0.0, maxDist, dist;        double red=0.0, green=0.0, blue=0.0, hue, s, v, f, p, q, t;        fprintf(stderr, "%s:  computing radial background...",          PROGNAME);        fflush(stderr);        hh = rpng2_info.height / 2;        hw = rpng2_info.width / 2;        /* variables for radial waves:         *   aoffset:  number of degrees to rotate hue [CURRENTLY NOT USED]         *   freq:  number of color beams originating from the center         *   grayspot:  size of the graying center area (anti-alias)         *   rotate:  rotation of the beams as a function of radius         *   saturate:  saturation of beams' shape azimuthally         */        angle = CLIP(angle, 0.0, 360.0);        grayspot = CLIP(bg[pat].bg_gray, 1, (hh + hw));        freq = MAX((double)bg[pat].bg_freq, 0.0);        saturate = (double)bg[pat].bg_bsat * 0.1;        rotate = (double)bg[pat].bg_brot * 0.1;        gray = 0.0;        intensity = 0.0;        maxDist = (double)((hw*hw) + (hh*hh));        for (row = 0;  row < rpng2_info.height;  ++row) {            y = row - hh;            dest = bg_data + row*bg_rowbytes;            for (i = 0;  i < rpng2_info.width;  ++i) {                x = i - hw;                angle = (x == 0)? PI_2 : atan((double)y / (double)x);                gray = (double)MAX(ABS(y), ABS(x)) / grayspot;                gray = MIN(1.0, gray);                dist = (double)((x*x) + (y*y)) / maxDist;                intensity = cos((angle+(rotate*dist*PI)) * freq) *                  gray * saturate;                intensity = (MAX(MIN(intensity,1.0),-1.0) + 1.0) * 0.5;                hue = (angle + PI) * INV_PI_360 + aoffset;                s = gray * ((double)(ABS(x)+ABS(y)) / (double)(hw + hh));                s = MIN(MAX(s,0.0), 1.0);                v = MIN(MAX(intensity,0.0), 1.0);                if (s == 0.0) {                    ch = (uch)(v * 255.0);                    *dest++ = ch;                    *dest++ = ch;                    *dest++ = ch;                } else {                    if ((hue < 0.0) || (hue >= 360.0))                        hue -= (((int)(hue / 360.0)) * 360.0);                    hue /= 60.0;                    ii = (int)hue;                    f = hue - (double)ii;                    p = (1.0 - s) * v;                    q = (1.0 - (s * f)) * v;                    t = (1.0 - (s * (1.0 - f))) * v;                    if      (ii == 0) { red = v; green = t; blue = p; }                    else if (ii == 1) { red = q; green = v; blue = p; }                    else if (ii == 2) { red = p; green = v; blue = t; }                    else if (ii == 3) { red = p; green = q; blue = v; }                    else if (ii == 4) { red = t; green = p; blue = v; }                    else if (ii == 5) { red = v; green = p; blue = q; }                    *dest++ = (uch)(red * 255.0);                    *dest++ = (uch)(green * 255.0);                    *dest++ = (uch)(blue * 255.0);                }            }        }        fprintf(stderr, "done.\n");        fflush(stderr);    }/*---------------------------------------------------------------------------    Blast background image to display buffer before beginning PNG decode;    calling function will handle invalidation and UpdateWindow() call.  ---------------------------------------------------------------------------*/    for (row = 0;  row < rpng2_info.height;  ++row) {        src = bg_data + row*bg_rowbytes;        dest = wimage_data + row*wimage_rowbytes;        for (i = rpng2_info.width;  i > 0;  --i) {            r1 = *src++;            g1 = *src++;            b1 = *src++;            *dest++ = b1;            *dest++ = g1;   /* note reverse order */            *dest++ = r1;        }    }    return 0;} /* end function rpng2_win_load_bg_image() */static void rpng2_win_display_row(ulg row){    uch bg_red   = rpng2_info.bg_red;    uch bg_green = rpng2_info.bg_green;    uch bg_blue  = rpng2_info.bg_blue;    uch *src, *src2=NULL, *dest;    uch r, g, b, a;    ulg i;    static int rows=0;    static ulg firstrow;/*---------------------------------------------------------------------------    rows and firstrow simply track how many rows (and which ones) have not    yet been displayed; alternatively, we could call InvalidateRect() for    every row and not bother with the records-keeping.  ---------------------------------------------------------------------------*/    Trace((stderr, "beginning rpng2_win_display_row()\n"))    if (rows == 0)        firstrow = row;   /* first row not yet displayed */    ++rows;   /* count of rows received but not yet displayed *//*---------------------------------------------------------------------------    Aside from the use of the rpng2_info struct and the lack of an outer    loop (over rows), this routine is identical to rpng_win_display_image()    in the non-progressive version of the program.  ---------------------------------------------------------------------------*/    src = rpng2_info.image_data + row*rpng2_info.rowbytes;    if (bg_image)        src2 = bg_data + row*bg_rowbytes;    dest = wimage_data + row*wimage_rowbytes;    if (rpng2_info.channels == 3) {        for (i = rpng2_info.width;  i > 0;  --i) {            r = *src++;            g = *src++;            b = *src++;            *dest++ = b;            *dest++ = g;   /* note reverse order */            *dest++ = r;        }    } else /* if (rpng2_info.channels == 4) */ {        for (i = rpng2_info.width;  i > 0;  --i) {            r = *src++;            g = *src++;            b = *src++;            a = *src++;            if (bg_image) {                bg_red   = *src2++;                bg_green = *src2++;                bg_blue  = *src2++;            }            if (a == 255) {                *dest++ = b;                *dest++ = g;                *dest++ = r;            } else if (a == 0) {                *dest++ = bg_blue;                *dest++ = bg_green;                *dest++ = bg_red;            } else {                /* this macro (copied from png.h) composites the                 * foreground and background values and puts the                 * result into the first argument; there are no                 * side effects with the first argument */                alpha_composite(*dest++, b, a, bg_blue);                alpha_composite(*dest++, g, a, bg_green);                alpha_composite(*dest++, r, a, bg_red);            }        }    }/*---------------------------------------------------------------------------    Display after every 16 rows or when on last row.  (Region may include    previously displayed lines due to interlacing--i.e., not contiguous.)  ---------------------------------------------------------------------------*/    if ((rows & 0xf) == 0 || row == rpng2_info.height-1) {        RECT rect;        rect.left = 0L;        rect.top = (LONG)firstrow;        rect.right = (LONG)rpng2_info.width;       /* possibly off by one? */        rect.bottom = (LONG)row + 1L;              /* possibly off by one? */        InvalidateRect(global_hwnd, &rect, FALSE);        UpdateWindow(global_hwnd);                 /* similar to XFlush() */        rows = 0;    }} /* end function rpng2_win_display_row() */static void rpng2_win_finish_display(){    Trace((stderr, "beginning rpng2_win_finish_display()\n"))    /* last row has already been displayed by rpng2_win_display_row(), so     * we have nothing to do here except set a flag and let the user know     * that the image is done */    rpng2_info.done = TRUE;    printf(      "Done.  Press Q, Esc or mouse button 1 (within image window) to quit.\n");    fflush(stdout);}static void rpng2_win_cleanup(){    if (bg_image && bg_data) {        free(bg_data);        bg_data = NULL;    }    if (rpng2_info.image_data) {        free(rpng2_info.image_data);        rpng2_info.image_data = NULL;    }    if (rpng2_info.row_pointers) {        free(rpng2_info.row_pointers);        rpng2_info.row_pointers = NULL;    }    if (dib) {        free(dib);        dib = NULL;    }}LRESULT CALLBACK rpng2_win_wndproc(HWND hwnd, UINT iMsg, WPARAM wP, LPARAM lP){    HDC         hdc;    PAINTSTRUCT ps;    int rc;    switch (iMsg) {        case WM_CREATE:            /* one-time processing here, if any */            return 0;        case WM_PAINT:            hdc = BeginPaint(hwnd, &ps);            rc = StretchDIBits(hdc, 0, 0, rpng2_info.width, rpng2_info.height,                                    0, 0, rpng2_info.width, rpng2_info.height,                                    wimage_data, (BITMAPINFO *)bmih,                                    0, SRCCOPY);            EndPaint(hwnd, &ps);            return 0;        /* wait for the user to tell us when to quit */        case WM_CHAR:            switch (wP) {       /* only need one, so ignore repeat count */                case 'q':                case 'Q':                case 0x1B:      /* Esc key */                    PostQuitMessage(0);            }            return 0;        case WM_LBUTTONDOWN:    /* another way of quitting */        case WM_DESTROY:            PostQuitMessage(0);            return 0;    }    return DefWindowProc(hwnd, iMsg, wP, lP);}