exit(2);
    }


    /* do the basic Windows initialization stuff, make the window and fill it
     * with the background color */

    if (rpng_win_create_window(hInst, showmode))
        exit(2);


    /* decode the image, all at once */

    Trace((stderr, "calling readpng_get_image()\n"))
    image_data = readpng_get_image(display_exponent, &image_channels,
      &image_rowbytes);
    Trace((stderr, "done with readpng_get_image()\n"))


    /* done with PNG file, so clean up to minimize memory usage (but do NOT
     * nuke image_data!) */

    readpng_cleanup(FALSE);
    fclose(infile);

    if (!image_data) {
        fprintf(stderr, PROGNAME ":  unable to decode PNG image\n");
        exit(3);
    }


    /* display image (composite with background if requested) */

    Trace((stderr, "calling rpng_win_display_image()\n"))
    if (rpng_win_display_image()) {
        free(image_data);
        exit(4);
    }
    Trace((stderr, "done with rpng_win_display_image()\n"))


    /* wait for the user to tell us when to quit */

    printf(
      "Done.  Press Q, Esc or mouse button 1 (within image window) to quit.\n");
    fflush(stdout);

    while (GetMessage(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }


    /* OK, we're done:  clean up all image and Windows resources and go away */

    rpng_win_cleanup();

    return msg.wParam;
}





static int rpng_win_create_window(HINSTANCE hInst, int showmode)
{
    uch *dest;
    int extra_width, extra_height;
    ulg i, j;
    WNDCLASSEX wndclass;


/*---------------------------------------------------------------------------
    Allocate memory for the display-specific version of the image (round up
    to multiple of 4 for Windows DIB).
  ---------------------------------------------------------------------------*/

    wimage_rowbytes = ((3*image_width + 3L) >> 2) << 2;

    if (!(dib = (uch *)malloc(sizeof(BITMAPINFOHEADER) +
                              wimage_rowbytes*image_height)))
    {
        return 4;   /* fail */
    }

/*---------------------------------------------------------------------------
    Initialize the DIB.  Negative height means to use top-down BMP ordering
    (must be uncompressed, but that's what we want).  Bit count of 1, 4 or 8
    implies a colormap of RGBX quads, but 24-bit BMPs just use B,G,R values
    directly => wimage_data begins immediately after BMP header.
  ---------------------------------------------------------------------------*/

    memset(dib, 0, sizeof(BITMAPINFOHEADER));
    bmih = (BITMAPINFOHEADER *)dib;
    bmih->biSize = sizeof(BITMAPINFOHEADER);
    bmih->biWidth = image_width;
    bmih->biHeight = -((long)image_height);
    bmih->biPlanes = 1;
    bmih->biBitCount = 24;
    bmih->biCompression = 0;
    wimage_data = dib + sizeof(BITMAPINFOHEADER);

/*---------------------------------------------------------------------------
    Fill in background color (black by default); data are in BGR order.
  ---------------------------------------------------------------------------*/

    for (j = 0;  j < image_height;  ++j) {
        dest = wimage_data + j*wimage_rowbytes;
        for (i = image_width;  i > 0;  --i) {
            *dest++ = bg_blue;
            *dest++ = bg_green;
            *dest++ = bg_red;
        }
    }

/*---------------------------------------------------------------------------
    Set the window parameters.
  ---------------------------------------------------------------------------*/

    memset(&wndclass, 0, sizeof(wndclass));

    wndclass.cbSize = sizeof(wndclass);
    wndclass.style = CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc = rpng_win_wndproc;
    wndclass.hInstance = hInst;
    wndclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wndclass.hCursor = LoadCursor(NULL, IDC_ARROW);
    wndclass.hbrBackground = (HBRUSH)GetStockObject(DKGRAY_BRUSH);
    wndclass.lpszMenuName = NULL;
    wndclass.lpszClassName = progname;
    wndclass.hIconSm = LoadIcon(NULL, IDI_APPLICATION);

    RegisterClassEx(&wndclass);

/*---------------------------------------------------------------------------
    Finally, create the window.
  ---------------------------------------------------------------------------*/

    extra_width  = 2*(GetSystemMetrics(SM_CXBORDER) +
                      GetSystemMetrics(SM_CXDLGFRAME));
    extra_height = 2*(GetSystemMetrics(SM_CYBORDER) +
                      GetSystemMetrics(SM_CYDLGFRAME)) +
                      GetSystemMetrics(SM_CYCAPTION);

    global_hwnd = CreateWindow(progname, titlebar, WS_OVERLAPPEDWINDOW,
      CW_USEDEFAULT, CW_USEDEFAULT, image_width+extra_width,
      image_height+extra_height, NULL, NULL, hInst, NULL);

    ShowWindow(global_hwnd, showmode);
    UpdateWindow(global_hwnd);

    return 0;

} /* end function rpng_win_create_window() */





static int rpng_win_display_image()
{
    uch *src, *dest;
    uch r, g, b, a;
    ulg i, row, lastrow;
    RECT rect;


    Trace((stderr, "beginning display loop (image_channels == %d)\n",
      image_channels))
    Trace((stderr, "(width = %ld, rowbytes = %ld, wimage_rowbytes = %d)\n",
      image_width, image_rowbytes, wimage_rowbytes))


/*---------------------------------------------------------------------------
    Blast image data to buffer.  This whole routine takes place before the
    message loop begins, so there's no real point in any pseudo-progressive
    display...
  ---------------------------------------------------------------------------*/

    for (lastrow = row = 0;  row < image_height;  ++row) {
        src = image_data + row*image_rowbytes;
        dest = wimage_data + row*wimage_rowbytes;
        if (image_channels == 3) {
            for (i = image_width;  i > 0;  --i) {
                r = *src++;
                g = *src++;
                b = *src++;
                *dest++ = b;
                *dest++ = g;   /* note reverse order */
                *dest++ = r;
            }
        } else /* if (image_channels == 4) */ {
            for (i = image_width;  i > 0;  --i) {
                r = *src++;
                g = *src++;
                b = *src++;
                a = *src++;
                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 lines */
        if (((row+1) & 0xf) == 0) {
            rect.left = 0L;
            rect.top = (LONG)lastrow;
            rect.right = (LONG)image_width;      /* possibly off by one? */
            rect.bottom = (LONG)lastrow + 16L;   /* possibly off by one? */
            InvalidateRect(global_hwnd, &rect, FALSE);
            UpdateWindow(global_hwnd);     /* similar to XFlush() */
            lastrow = row + 1;
        }
    }

    Trace((stderr, "calling final image-flush routine\n"))
    if (lastrow < image_height) {
        rect.left = 0L;
        rect.top = (LONG)lastrow;
        rect.right = (LONG)image_width;      /* possibly off by one? */
        rect.bottom = (LONG)image_height;    /* possibly off by one? */
        InvalidateRect(global_hwnd, &rect, FALSE);
        UpdateWindow(global_hwnd);     /* similar to XFlush() */
    }

/*
    last param determines whether or not background is wiped before paint
    InvalidateRect(global_hwnd, NULL, TRUE);
    UpdateWindow(global_hwnd);
 */

    return 0;
}





static void rpng_win_cleanup()
{
    if (image_data) {
        free(image_data);
        image_data = NULL;
    }

    if (dib) {
        free(dib);
        dib = NULL;
    }
}





LRESULT CALLBACK rpng_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);
                    /*                    dest                          */
            rc = StretchDIBits(hdc, 0, 0, image_width, image_height,
                    /*                    source                        */
                                    0, 0, image_width, image_height,
                                    wimage_data, (BITMAPINFO *)bmih,
                    /*              iUsage: no clue                     */
                                    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);
}