libpng/contrib/gregbook/rpng2-win.c

/*---------------------------------------------------------------------------

   rpng2 - progressive-model PNG display program                rpng2-win.c

   This program decodes and displays PNG files progressively, as if it were
   a web browser (though the front end is only set up to read from files).
   It supports gamma correction, user-specified background colors, and user-
   specified background patterns (for transparent images).  This version is
   for 32-bit Windows; it may compile under 16-bit Windows with a little
   tweaking (or maybe not).  Thanks to Adam Costello and Pieter S. van der
   Meulen for the "diamond" and "radial waves" patterns, respectively.

   to do:
    - handle quoted command-line args (especially filenames with spaces)
    - finish resizable checkerboard-gradient (sizes 4-128?)
    - use %.1023s to simplify truncation of title-bar string?
    - have minimum window width:  oh well

  ---------------------------------------------------------------------------

   Changelog:
    - 1.01:  initial public release
    - 1.02:  fixed cut-and-paste error in usage screen (oops...)
    - 1.03:  modified to allow abbreviated options
    - 1.04:  removed bogus extra argument from usage fprintf() [Glenn R-P?];
              fixed command-line parsing bug
    - 1.10:  enabled "message window"/console (thanks to David Geldreich)
    - 1.20:  added runtime MMX-enabling/disabling and new -mmx* options
    - 1.21:  made minor tweak to usage screen to fit within 25-line console

  ---------------------------------------------------------------------------

      Copyright (c) 1998-2001 Greg Roelofs.  All rights reserved.

      This software is provided "as is," without warranty of any kind,
      express or implied.  In no event shall the author or contributors
      be held liable for any damages arising in any way from the use of
      this software.

      Permission is granted to anyone to use this software for any purpose,
      including commercial applications, and to alter it and redistribute
      it freely, subject to the following restrictions:

      1. Redistributions of source code must retain the above copyright
         notice, disclaimer, and this list of conditions.
      2. Redistributions in binary form must reproduce the above copyright
         notice, disclaimer, and this list of conditions in the documenta-
         tion and/or other materials provided with the distribution.
      3. All advertising materials mentioning features or use of this
         software must display the following acknowledgment:

            This product includes software developed by Greg Roelofs
            and contributors for the book, "PNG: The Definitive Guide,"
            published by O'Reilly and Associates.

  ---------------------------------------------------------------------------*/

#define PROGNAME  "rpng2-win"
#define LONGNAME  "Progressive PNG Viewer for Windows"
#define VERSION   "1.21 of 29 June 2001"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <setjmp.h>    /* for jmpbuf declaration in readpng2.h */
#include <time.h>
#include <math.h>      /* only for PvdM background code */
#include <windows.h>
#include <conio.h>     /* only for _getch() */

/* all for PvdM background code: */
#ifndef PI
#  define PI             3.141592653589793238
#endif
#define PI_2             (PI*0.5)
#define INV_PI_360       (360.0 / PI)
#define MAX(a,b)         (a>b?a:b)
#define MIN(a,b)         (a<b?a:b)
#define CLIP(a,min,max)  MAX(min,MIN((a),max))
#define ABS(a)           ((a)<0?-(a):(a))
#define CLIP8P(c)        MAX(0,(MIN((c),255)))   /* 8-bit pos. integer (uch) */
#define ROUNDF(f)        ((int)(f + 0.5))

#define rgb1_max   bg_freq
#define rgb1_min   bg_gray
#define rgb2_max   bg_bsat
#define rgb2_min   bg_brot

/* #define DEBUG */     /* this enables the Trace() macros */

#include "readpng2.h"   /* typedefs, common macros, readpng2 prototypes */


/* could just include png.h, but this macro is the only thing we need
 * (name and typedefs changed to local versions); note that side effects
 * only happen with alpha (which could easily be avoided with
 * "ush acopy = (alpha);") */

#define alpha_composite(composite, fg, alpha, bg) {               \
    ush temp = ((ush)(fg)*(ush)(alpha) +                          \
                (ush)(bg)*(ush)(255 - (ush)(alpha)) + (ush)128);  \
    (composite) = (uch)((temp + (temp >> 8)) >> 8);               \
}


#define INBUFSIZE 4096   /* with pseudo-timing on (1 sec delay/block), this
                          *  block size corresponds roughly to a download
                          *  speed 10% faster than theoretical 33.6K maximum
                          *  (assuming 8 data bits, 1 stop bit and no other
                          *  overhead) */

/* local prototypes */
static void       rpng2_win_init(void);
static int        rpng2_win_create_window(void);
static int        rpng2_win_load_bg_image(void);
static void       rpng2_win_display_row(ulg row);
static void       rpng2_win_finish_display(void);
static void       rpng2_win_cleanup(void);
LRESULT CALLBACK  rpng2_win_wndproc(HWND, UINT, WPARAM, LPARAM);


static char titlebar[1024], *window_name = titlebar;
static char *progname = PROGNAME;
static char *appname = LONGNAME;
static char *icon_name = PROGNAME;    /* GRR:  not (yet) used */
static char *filename;
static FILE *infile;

static mainprog_info rpng2_info;

static uch inbuf[INBUFSIZE];
static int incount;

static int pat = 6;         /* must be less than num_bgpat */
static int bg_image = 0;
static int bgscale = 16;
static ulg bg_rowbytes;
static uch *bg_data;

static struct rgb_color {
    uch r, g, b;
} rgb[] = {
    {  0,   0,   0},    /*  0:  black */
    {255, 255, 255},    /*  1:  white */
    {173, 132,  57},    /*  2:  tan */
    { 64, 132,   0},    /*  3:  medium green */
    {189, 117,   1},    /*  4:  gold */
    {253, 249,   1},    /*  5:  yellow */
    {  0,   0, 255},    /*  6:  blue */
    {  0,   0, 120},    /*  7:  medium blue */
    {255,   0, 255},    /*  8:  magenta */
    { 64,   0,  64},    /*  9:  dark magenta */
    {255,   0,   0},    /* 10:  red */
    { 64,   0,   0},    /* 11:  dark red */
    {255, 127,   0},    /* 12:  orange */
    {192,  96,   0},    /* 13:  darker orange */
    { 24,  60,   0},    /* 14:  dark green-yellow */
    { 85, 125, 200}     /* 15:  ice blue */
};
/* not used for now, but should be for error-checking:
static int num_rgb = sizeof(rgb) / sizeof(struct rgb_color);
 */

/*
    This whole struct is a fairly cheesy way to keep the number of
    command-line options to a minimum.  The radial-waves background
    type is a particularly poor fit to the integer elements of the
    struct...but a few macros and a little fixed-point math will do
    wonders for ya.

    type bits:
       F E D C B A 9 8 7 6 5 4 3 2 1 0
                             | | | | |
                             | | +-+-+-- 0 = sharp-edged checkerboard
                             | |         1 = soft diamonds
                             | |         2 = radial waves
                             | |       3-7 = undefined
                             | +-- gradient #2 inverted?
                             +-- alternating columns inverted?
 */
static struct background_pattern {
    ush type;
    int rgb1_max, rgb1_min;     /* or bg_freq, bg_gray */
    int rgb2_max, rgb2_min;     /* or bg_bsat, bg_brot (both scaled by 10)*/
} bg[] = {
    {0+8,   2,0,  1,15},        /* checkered:  tan/black vs. white/ice blue */
    {0+24,  2,0,  1,0},         /* checkered:  tan/black vs. white/black */
    {0+8,   4,5,  0,2},         /* checkered:  gold/yellow vs. black/tan */
    {0+8,   4,5,  0,6},         /* checkered:  gold/yellow vs. black/blue */
    {0,     7,0,  8,9},         /* checkered:  deep blue/black vs. magenta */
    {0+8,  13,0,  5,14},        /* checkered:  orange/black vs. yellow */
    {0+8,  12,0, 10,11},        /* checkered:  orange/black vs. red */
    {1,     7,0,  8,0},         /* diamonds:  deep blue/black vs. magenta */
    {1,    12,0, 11,0},         /* diamonds:  orange vs. dark red */
    {1,    10,0,  7,0},         /* diamonds:  red vs. medium blue */
    {1,     4,0,  5,0},         /* diamonds:  gold vs. yellow */
    {1,     3,0,  0,0},         /* diamonds:  medium green vs. black */
    {2,    16, 100,  20,   0},  /* radial:  ~hard radial color-beams */
    {2,    18, 100,  10,   2},  /* radial:  soft, curved radial color-beams */
    {2,    16, 256, 100, 250},  /* radial:  very tight spiral */
    {2, 10000, 256,  11,   0}   /* radial:  dipole-moire' (almost fractal) */
};
static int num_bgpat = sizeof(bg) / sizeof(struct background_pattern);


/* Windows-specific global variables (could go in struct, but messy...) */
static ulg wimage_rowbytes;
static uch *dib;
static uch *wimage_data;
static BITMAPINFOHEADER *bmih;

static HWND global_hwnd;
static HINSTANCE global_hInst;
static int global_showmode;




int WINAPI WinMain(HINSTANCE hInst, HINSTANCE hPrevInst, PSTR cmd, int showmode)
{
    char *args[1024];                 /* arbitrary limit, but should suffice */
    char **argv = args;
    char *p, *q, *bgstr = NULL;
    int argc = 0;
    int rc, alen, flen;
    int error = 0;
    int timing = FALSE;
    int have_bg = FALSE;
    double LUT_exponent;              /* just the lookup table */
    double CRT_exponent = 2.2;        /* just the monitor */
    double default_display_exponent;  /* whole display system */
    MSG msg;


    /* First initialize a few things, just to be sure--memset takes care of
     * default background color (black), booleans (FALSE), pointers (NULL),
     * etc. */

    global_hInst = hInst;
    global_showmode = showmode;
    filename = (char *)NULL;
    memset(&rpng2_info, 0, sizeof(mainprog_info));


    /* Next reenable console output, which normally goes to the bit bucket
     * for windowed apps.  Closing the console window will terminate the
     * app.  Thanks to David.Geldreich@realviz.com for supplying the magical
     * incantation. */

    AllocConsole();
    freopen("CONOUT$", "a", stderr);
    freopen("CONOUT$", "a", stdout);


    /* Set the default value for our display-system exponent, i.e., the
     * product of the CRT exponent and the exponent corresponding to
     * the frame-buffer's lookup table (LUT), if any.  This is not an
     * exhaustive list of LUT values (e.g., OpenStep has a lot of weird
     * ones), but it should cover 99% of the current possibilities.  And
     * yes, these ifdefs are completely wasted in a Windows program... */

#if defined(NeXT)
    /* third-party utilities can modify the default LUT exponent */
    LUT_exponent = 1.0 / 2.2;
    /*
    if (some_next_function_that_returns_gamma(&next_gamma))
        LUT_exponent = 1.0 / next_gamma;
     */
#elif defined(sgi)
    LUT_exponent = 1.0 / 1.7;
    /* there doesn't seem to be any documented function to
     * get the "gamma" value, so we do it the hard way */
    infile = fopen("/etc/config/system.glGammaVal", "r");
    if (infile) {
        double sgi_gamma;

        fgets(tmpline, 80, infile);
        fclose(infile);
        sgi_gamma = atof(tmpline);
        if (sgi_gamma > 0.0)
            LUT_exponent = 1.0 / sgi_gamma;
    }
#elif defined(Macintosh)
    LUT_exponent = 1.8 / 2.61;
    /*
    if (some_mac_function_that_returns_gamma(&mac_gamma))
        LUT_exponent = mac_gamma / 2.61;
     */
#else
    LUT_exponent = 1.0;   /* assume no LUT:  most PCs */
#endif

    /* the defaults above give 1.0, 1.3, 1.5 and 2.2, respectively: */
    default_display_exponent = LUT_exponent * CRT_exponent;


    /* If the user has set the SCREEN_GAMMA environment variable as suggested
     * (somewhat imprecisely) in the libpng documentation, use that; otherwise
     * use the default value we just calculated.  Either way, the user may
     * override this via a command-line option. */

    if ((p = getenv("SCREEN_GAMMA")) != NULL)
        rpng2_info.display_exponent = atof(p);
    else
        rpng2_info.display_exponent = default_display_exponent;


    /* Windows really hates command lines, so we have to set up our own argv.
     * Note that we do NOT bother with quoted arguments here, so don't use
     * filenames with spaces in 'em! */

    argv[argc++] = PROGNAME;
    p = cmd;
    for (;;) {
        if (*p == ' ')
            while (*++p == ' ')
                ;
        /* now p points at the first non-space after some spaces */
        if (*p == '\0')
            break;    /* nothing after the spaces:  done */
        argv[argc++] = q = p;
        while (*q && *q != ' ')
            ++q;
        /* now q points at a space or the end of the string */
        if (*q == '\0')
            break;    /* last argv already terminated; quit */
        *q = '\0';    /* change space to terminator */
        p = q + 1;
    }
    argv[argc] = NULL;   /* terminate the argv array itself */


    /* Now parse the command line for options and the PNG filename. */

    while (*++argv && !error) {
        if (!strncmp(*argv, "-gamma", 2)) {
            if (!*++argv)
                ++error;
            else {
                rpng2_info.display_exponent = atof(*argv);
                if (rpng2_info.display_exponent <= 0.0)
                    ++error;
            }
        } else if (!strncmp(*argv, "-bgcolor", 4)) {
            if (!*++argv)
                ++error;
            else {
                bgstr = *argv;
                if (strlen(bgstr) != 7 || bgstr[0] != '#')
                    ++error;
                else {
                    have_bg = TRUE;
                    bg_image = FALSE;
                }
            }
        } else if (!strncmp(*argv, "-bgpat", 4)) {
            if (!*++argv)
                ++error;
            else {
                pat = atoi(*argv) - 1;
                if (pat < 0 || pat >= num_bgpat)
                    ++error;
                else {
                    bg_image = TRUE;
                    have_bg = FALSE;
                }
            }
        } else if (!strncmp(*argv, "-timing", 2)) {
            timing = TRUE;
#if (defined(__i386__) || defined(_M_IX86))
        } else if (!strncmp(*argv, "-nommxfilters", 7)) {
            rpng2_info.nommxfilters = TRUE;
        } else if (!strncmp(*argv, "-nommxcombine", 7)) {
            rpng2_info.nommxcombine = TRUE;
        } else if (!strncmp(*argv, "-nommxinterlace", 7)) {
            rpng2_info.nommxinterlace = TRUE;
        } else if (!strcmp(*argv, "-nommx")) {
            rpng2_info.nommxfilters = TRUE;
            rpng2_info.nommxcombine = TRUE;
            rpng2_info.nommxinterlace = TRUE;
#endif
        } else {
            if (**argv != '-') {
                filename = *argv;
                if (argv[1])   /* shouldn't be any more args after filename */
                    ++error;
            } else
                ++error;   /* not expecting any other options */
        }
    }

    if (!filename) {
        ++error;
    } else if (!(infile = fopen(filename, "rb"))) {
        fprintf(stderr, PROGNAME ":  can't open PNG file [%s]\n", filename);
        ++error;
    } else {
        incount = fread(inbuf, 1, INBUFSIZE, infile);
        if (incount < 8 || !readpng2_check_sig(inbuf, 8)) {
            fprintf(stderr, PROGNAME
              ":  [%s] is not a PNG file: incorrect signature\n",
              filename);
            ++error;
        } else if ((rc = readpng2_init(&rpng2_info)) != 0) {
            switch (rc) {
                case 2:
                    fprintf(stderr, PROGNAME
                      ":  [%s] has bad IHDR (libpng longjmp)\n",
                      filename);
                    break;
                case 4:
                    fprintf(stderr, PROGNAME ":  insufficient memory\n");
                    break;
                default:
                    fprintf(stderr, PROGNAME
                      ":  unknown readpng2_init() error\n");
                    break;
            }
            ++error;
        }
        if (error)
            fclose(infile);
    }


    /* usage screen */

    if (error) {
        int ch;

        fprintf(stderr, "\n%s %s:  %s\n\n", PROGNAME, VERSION, appname);
        readpng2_version_info();
        fprintf(stderr, "\n"
          "Usage:  %s [-gamma exp] [-bgcolor bg | -bgpat pat] [-timing]\n"
#if (defined(__i386__) || defined(_M_IX86))
          "        %*s [[-nommxfilters] [-nommxcombine] [-nommxinterlace] | -nommx]\n"
#endif
          "        %*s file.png\n\n"
          "    exp \ttransfer-function exponent (``gamma'') of the display\n"
          "\t\t  system in floating-point format (e.g., ``%.1f''); equal\n"
          "\t\t  to the product of the lookup-table exponent (varies)\n"
          "\t\t  and the CRT exponent (usually 2.2); must be positive\n"
          "    bg  \tdesired background color in 7-character hex RGB format\n"
          "\t\t  (e.g., ``#ff7700'' for orange:  same as HTML colors);\n"
          "\t\t  used with transparent images; overrides -bgpat option\n"
          "    pat \tdesired background pattern number (1-%d); used with\n"
          "\t\t  transparent images; overrides -bgcolor option\n"
          "    -timing\tenables delay for every block read, to simulate modem\n"
          "\t\t  download of image (~36 Kbps)\n"
#if (defined(__i386__) || defined(_M_IX86))
          "    -nommx*\tdisable optimized MMX routines for decoding row filters,\n"
          "\t\t  combining rows, and expanding interlacing, respectively\n"
#endif
          "\nPress Q, Esc or mouse button 1 after image is displayed to quit.\n"
          "Press Q or Esc to quit this usage screen. ",
          PROGNAME,
#if (defined(__i386__) || defined(_M_IX86))
          strlen(PROGNAME), " ",
#endif
          strlen(PROGNAME), " ", default_display_exponent, num_bgpat);
        fflush(stderr);
        do
            ch = _getch();
        while (ch != 'q' && ch != 'Q' && ch != 0x1B);
        exit(1);
    } else {
        fprintf(stderr, "\n%s %s:  %s\n", PROGNAME, VERSION, appname);
        fprintf(stderr,
          "\n   [console window:  closing this window will terminate %s]\n\n",
          PROGNAME);
        fflush(stderr);
    }


    /* set the title-bar string, but make sure buffer doesn't overflow */

    alen = strlen(appname);
    flen = strlen(filename);
    if (alen + flen + 3 > 1023)
        sprintf(titlebar, "%s:  ...%s", appname, filename+(alen+flen+6-1023));
    else
        sprintf(titlebar, "%s:  %s", appname, filename);


    /* set some final rpng2_info variables before entering main data loop */

    if (have_bg) {
        unsigned r, g, b;   /* this approach quiets compiler warnings */

        sscanf(bgstr+1, "%2x%2x%2x", &r, &g, &b);
        rpng2_info.bg_red   = (uch)r;
        rpng2_info.bg_green = (uch)g;
        rpng2_info.bg_blue  = (uch)b;
    } else
        rpng2_info.need_bgcolor = TRUE;

    rpng2_info.done = FALSE;
    rpng2_info.mainprog_init = rpng2_win_init;
    rpng2_info.mainprog_display_row = rpng2_win_display_row;
    rpng2_info.mainprog_finish_display = rpng2_win_finish_display;


    /* OK, this is the fun part:  call readpng2_decode_data() at the start of
     * the loop to deal with our first buffer of data (read in above to verify
     * that the file is a PNG image), then loop through the file and continue
     * calling the same routine to handle each chunk of data.  It in turn
     * passes the data to libpng, which will invoke one or more of our call-
     * backs as decoded data become available.  We optionally call Sleep() for
     * one second per iteration to simulate downloading the image via an analog
     * modem. */

    for (;;) {
        Trace((stderr, "about to call readpng2_decode_data()\n"))
        if (readpng2_decode_data(&rpng2_info, inbuf, incount))
            ++error;
        Trace((stderr, "done with readpng2_decode_data()\n"))
        if (error || feof(infile) || rpng2_info.done)
            break;
        if (timing)
            Sleep(1000L);
        incount = fread(inbuf, 1, INBUFSIZE, infile);
    }


    /* clean up PNG stuff and report any decoding errors */

    fclose(infile);
    Trace((stderr, "about to call readpng2_cleanup()\n"))
    readpng2_cleanup(&rpng2_info);

    if (error) {
        fprintf(stderr, PROGNAME ":  libpng error while decoding PNG image\n");
        exit(3);
    }


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

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


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

    Trace((stderr, "about to call rpng2_win_cleanup()\n"))
    rpng2_win_cleanup();

    return msg.wParam;
}





/* this function is called by readpng2_info_callback() in readpng2.c, which
 * in turn is called by libpng after all of the pre-IDAT chunks have been
 * read and processed--i.e., we now have enough info to finish initializing */

static void rpng2_win_init()
{
    ulg i;
    ulg rowbytes = rpng2_info.rowbytes;

    Trace((stderr, "beginning rpng2_win_init()\n"))
    Trace((stderr, "  rowbytes = %ld\n", rpng2_info.rowbytes))
    Trace((stderr, "  width  = %ld\n", rpng2_info.width))
    Trace((stderr, "  height = %ld\n", rpng2_info.height))

    rpng2_info.image_data = (uch *)malloc(rowbytes * rpng2_info.height);
    if (!rpng2_info.image_data) {
        readpng2_cleanup(&rpng2_info);
        return;
    }

    rpng2_info.row_pointers = (uch **)malloc(rpng2_info.height * sizeof(uch *));
    if (!rpng2_info.row_pointers) {
        free(rpng2_info.image_data);
        rpng2_info.image_data = NULL;
        readpng2_cleanup(&rpng2_info);
        return;
    }

    for (i = 0;  i < rpng2_info.height;  ++i)
        rpng2_info.row_pointers[i] = rpng2_info.image_data + i*rowbytes;

/*---------------------------------------------------------------------------
    Do the basic Windows initialization stuff, make the window, and fill it
    with the user-specified, file-specified or default background color.
  ---------------------------------------------------------------------------*/

    if (rpng2_win_create_window()) {
        readpng2_cleanup(&rpng2_info);
        return;
    }
}





static int rpng2_win_create_window()
{
    uch bg_red   = rpng2_info.bg_red;
    uch bg_green = rpng2_info.bg_green;
    uch bg_blue  = rpng2_info.bg_blue;
    uch *dest;
    int extra_width, extra_height;
    ulg i, j;
    WNDCLASSEX wndclass;
    RECT rect;


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

    wimage_rowbytes = ((3*rpng2_info.width + 3L) >> 2) << 2;

    if (!(dib = (uch *)malloc(sizeof(BITMAPINFOHEADER) +
                              wimage_rowbytes*rpng2_info.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 = rpng2_info.width;
    bmih->biHeight = -((long)rpng2_info.height);
    bmih->biPlanes = 1;
    bmih->biBitCount = 24;
    bmih->biCompression = 0;
    wimage_data = dib + sizeof(BITMAPINFOHEADER);

/*---------------------------------------------------------------------------
    Fill window with the specified background color (default is black), but
    defer loading faked "background image" until window is displayed (may be
    slow to compute).  Data are in BGR order.
  ---------------------------------------------------------------------------*/

    if (bg_image) {   /* just fill with black for now */
        memset(wimage_data, 0, wimage_rowbytes*rpng2_info.height);
    } else {
        for (j = 0;  j < rpng2_info.height;  ++j) {
            dest = wimage_data + j*wimage_rowbytes;
            for (i = rpng2_info.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 = rpng2_win_wndproc;
    wndclass.hInstance = global_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, rpng2_info.width+extra_width,
      rpng2_info.height+extra_height, NULL, NULL, global_hInst, NULL);

    ShowWindow(global_hwnd, global_showmode);
    UpdateWindow(global_hwnd);

/*---------------------------------------------------------------------------
    Now compute the background image and display it.  If it fails (memory
    allocation), revert to a plain background color.
  ---------------------------------------------------------------------------*/

    if (bg_image) {
        static const char *msg = "Computing background image...";
        int x, y, len = strlen(msg);
        HDC hdc = GetDC(global_hwnd);
        TEXTMETRIC tm;

        GetTextMetrics(hdc, &tm);
        x = (rpng2_info.width - len*tm.tmAveCharWidth)/2;
        y = (rpng2_info.height - tm.tmHeight)/2;
        SetBkMode(hdc, TRANSPARENT);
        SetTextColor(hdc, GetSysColor(COLOR_HIGHLIGHTTEXT));
        /* this can still begin out of bounds even if x is positive (???): */
        TextOut(hdc, ((x < 0)? 0 : x), ((y < 0)? 0 : y), msg, len);
        ReleaseDC(global_hwnd, hdc);

        rpng2_win_load_bg_image();   /* resets bg_image if fails */
    }

    if (!bg_image) {
        for (j = 0;  j < rpng2_info.height;  ++j) {
            dest = wimage_data + j*wimage_rowbytes;
            for (i = rpng2_info.width;  i > 0;  --i) {
                *dest++ = bg_blue;
                *dest++ = bg_green;
                *dest++ = bg_red;
            }
        }
    }

    rect.left = 0L;
    rect.top = 0L;
    rect.right = (LONG)rpng2_info.width;       /* possibly off by one? */
    rect.bottom = (LONG)rpng2_info.height;     /* possibly off by one? */
    InvalidateRect(global_hwnd, &rect, FALSE);
    UpdateWindow(global_hwnd);                 /* similar to XFlush() */

    return 0;

} /* end function rpng2_win_create_window() */





static int rpng2_win_load_bg_image()
{
    uch *src, *dest;
    uch r1, r2, g1, g2, b1, b2;
    uch r1_inv, r2_inv, g1_inv, g2_inv, b1_inv, b2_inv;
    int k, hmax, max;
    int xidx, yidx, yidx_max = (bgscale-1);
    int even_odd_vert, even_odd_horiz, even_odd;
    int invert_gradient2 = (bg[pat].type & 0x08);
    int invert_column;
    ulg i, row;

/*---------------------------------------------------------------------------
    Allocate buffer for fake background image to be used with transparent
    images; if this fails, revert to plain background color.
  ---------------------------------------------------------------------------*/

    bg_rowbytes = 3 * rpng2_info.width;
    bg_data = (uch *)malloc(bg_rowbytes * rpng2_info.height);
    if (!bg_data) {
        fprintf(stderr, PROGNAME
          ":  unable to allocate memory for background image\n");
        bg_image = 0;
        return 1;
    }

/*---------------------------------------------------------------------------
    Vertical gradients (ramps) in NxN squares, alternating direction and
    colors (N == bgscale).
  ---------------------------------------------------------------------------*/

    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);
}