/*-
 * giftoppm.c - Converts from a Compuserve GIF (tm) image to a PPM file.
 *
 * Copyright (c) 1988, 1989 by Patrick J. Naughton
 *
 * Author: Patrick J. Naughton
 * naughton@wind.sun.com
 *
 * Permission to use, copy, modify, and distribute this software and its
 * documentation for any purpose and without fee is hereby granted,
 * provided that the above copyright notice appear in all copies and that
 * both that copyright notice and this permission notice appear in
 * supporting documentation.
 *
 * This file is provided AS IS with no warranties of any kind.  The author
 * shall have no liability with respect to the infringement of copyrights,
 * trade secrets or any patents by this file or any part thereof.  In no
 * event will the author be liable for any lost revenue or profits or
 * other special, indirect and consequential damages.
 *
 * Comments and additions should be sent to the author:
 *
 *                     Patrick J. Naughton
 *                     Sun Microsystems
 *                     2550 Garcia Ave, MS 14-40
 *                     Mountain View, CA 94043
 *                     (415) 336-1080
 *
 * Revision History:
 * 15-Apr-89: (JP) Changed to use pbm_ error routines.
 * 23-Feb-89: (JP) Changed from PBM to PPM.
 * 03-Feb-89: (JP) Changed u_char to unsigned char, and unincluded types.h.
 * 01-Jan-89: Added error checking and removed NEXTSHORT.
 * 07-Sep-88: Added BytesPerScanline fix.
 * 30-Aug-88: Allow stdin/stdout. Restructured argument parser.
 * 28-Aug-88: (JP) Modified to output PBM instead of Sun raster.
 * 27-Jul-88: Updated to use libpixrect to fix 386i byteswapping problems.
 * 11-Apr-88: Converted to C and changed to write Sun rasterfiles.
 * 19-Jan-88: GIFSLOW.PAS posted to comp.graphics by Jim Briebel,
 *            a Turbo Pascal 4.0 program to painfully slowly display
 *            GIF images on an EGA equipped IBM-PC.
 *
 * Description:
 *   This program takes a Compuserve "Graphics Interchange Format" or "GIF"
 * file as input and writes a PPM file.
 *
 * Portability:
 *   To make this program convert to some image format other than PPM
 * format simply seach for the tag "PPMS:" in the source and
 * replace these simple mechanisms with the appropriate ones for the
 * other output format.  I have marked all (six) PPM Specific pieces
 * of code with this comment.
 *
 * PPMS: compile with "cc -o giftoppm -O giftoppm.c libppm.a
 */

#include <X11/Intrinsi.h>
#include <stdio.h>
#if  defined(SYSV) || defined(SVR4)
#include <string.h>
#else	/* SYSV */
#include <strings.h>
#endif	/* SYSV */

/*EJB*/
struct rgb_color {
        unsigned int red, green, blue;
        int pix_len;
};



typedef int boolean;

#define NEXTBYTE (*ptr++)
#define IMAGESEP 0x2c
#define INTERLACEMASK 0x40
#define COLORMAPMASK 0x80


int BitOffset = 0,		/* Bit Offset of next code */
    XC = 0, YC = 0,		/* Output X and Y coords of current pixel */
    Pass = 0,			/* Used by output routine if interlaced pic */
    OutCount = 0,		/* Decompressor output 'stack count' */
    RWidth, RHeight,		/* screen dimensions */
    Width, Height,		/* image dimensions */
    LeftOfs, TopOfs,		/* image offset */
    BitsPerPixel,		/* Bits per pixel, read from GIF header */
    BytesPerScanline,		/* bytes per scanline in output raster */
    ColorMapSize,		/* number of colors */
    CodeSize,			/* Code size, read from GIF header */
    InitCodeSize,		/* Starting code size, used during Clear */
    Code,			/* Value returned by ReadCode */
    MaxCode,			/* limiting value for current code size */
    ClearCode,			/* GIF clear code */
    EOFCode,			/* GIF end-of-information code */
    CurCode, OldCode, InCode,	/* Decompressor variables */
    FirstFree,			/* First free code, generated per GIF spec */
    FreeCode,			/* Decompressor, next free slot in hash table */
    FinChar,			/* Decompressor variable */
    BitMask,			/* AND mask for data size */
    ReadMask;			/* Code AND mask for current code size */

boolean Interlace, HasColormap;

/*EJB*/
unsigned char *pixels;

unsigned char *RawGIF;			/* The heap array to hold it, raw */
unsigned char *Raster;			/* The raster data stream, unblocked */

    /* The hash table used by the decompressor */
int Prefix[4096];
int Suffix[4096];

    /* An output array used by the decompressor */
int OutCode[1025];

    /* The color map, read from the GIF header */
unsigned char Red[256], Green[256], Blue[256];

char *id = "GIF87a";

unsigned char *ReadGifBitmap(fp, w, h, colrs)
FILE *fp;
int *w, *h;
struct rgb_color *colrs;
{
    int filesize;
    int scale;
    register unsigned char ch, ch1;
    register unsigned char *ptr, *ptr1;
    unsigned char *bitp;
    register int i;

    fseek(fp, 0L, 0);

    ptr = (unsigned char *) malloc(strlen(id) + 1);
    fread(ptr, strlen(id) + 1, 1, fp);
    if (strncmp(ptr, id, 6))
    {
	free(ptr);
	return((unsigned char *)NULL);
    }
    free(ptr);

    fseek(fp, 0L, 0);
    /* find the size of the file */
    fseek(fp, 0L, 2);
    filesize = ftell(fp);
    fseek(fp, 0L, 0);

    if (!(ptr = RawGIF = (unsigned char *) malloc(filesize)))
	fprintf(stderr, "not enough memory to read gif file\n");

    if (!(Raster = (unsigned char *) malloc(filesize)))
	fprintf(stderr, "not enough memory to read gif file\n");

    if (fread(ptr, filesize, 1, fp) != 1)
	fprintf(stderr, "GIF data read failed\n");

    ptr += 6;

/* Initialize variables */
    BitOffset = 0;
    XC = 0;
    YC = 0;
    Pass = 0;
    OutCount = 0;

/* Get variables from the GIF screen descriptor */

    ch = NEXTBYTE;
    RWidth = ch + 0x100 * NEXTBYTE;	/* screen dimensions... not used. */
    ch = NEXTBYTE;
    RHeight = ch + 0x100 * NEXTBYTE;

    ch = NEXTBYTE;
    HasColormap = ((ch & COLORMAPMASK) ? True : False);

    BitsPerPixel = (ch & 7) + 1;
    ColorMapSize = 1 << BitsPerPixel;
    BitMask = ColorMapSize - 1;

    ch = NEXTBYTE;		/* background color... not used. */

    if (NEXTBYTE)		/* supposed to be NULL */
	fprintf(stderr, "Corrupt GIF file (nonull)\n");

/* Read in global colormap. */

    if (HasColormap) {
	for (i = 0; i < ColorMapSize; i++) {
	    Red[i] = NEXTBYTE;
	    Green[i] = NEXTBYTE;
	    Blue[i] = NEXTBYTE;
	}

	/* PPMS: Don't have to do anything special here. */
    }
    else fprintf(stderr, "does not have a colormap\n");


/* Check for image seperator */

    if (NEXTBYTE != IMAGESEP)
	fprintf(stderr, "Corrupt GIF file (nosep)\n");

/* Now read in values from the image descriptor */

    ch = NEXTBYTE;
    LeftOfs = ch + 0x100 * NEXTBYTE;
    ch = NEXTBYTE;
    TopOfs = ch + 0x100 * NEXTBYTE;
    ch = NEXTBYTE;
    Width = ch + 0x100 * NEXTBYTE;
    ch = NEXTBYTE;
    Height = ch + 0x100 * NEXTBYTE;
    Interlace = ((NEXTBYTE & INTERLACEMASK) ? True : False);

    


/* Note that I ignore the possible existence of a local color map.
 * I'm told there aren't many files around that use them, and the spec
 * says it's defined for future use.  This could lead to an error
 * reading some files. 
 */

/* Start reading the raster data. First we get the intial code size
 * and compute decompressor constant values, based on this code size.
 */

    CodeSize = NEXTBYTE;
    ClearCode = (1 << CodeSize);
    EOFCode = ClearCode + 1;
    FreeCode = FirstFree = ClearCode + 2;

/* The GIF spec has it that the code size is the code size used to
 * compute the above values is the code size given in the file, but the
 * code size used in compression/decompression is the code size given in
 * the file plus one. (thus the ++).
 */

    CodeSize++;
    InitCodeSize = CodeSize;
    MaxCode = (1 << CodeSize);
    ReadMask = MaxCode - 1;

/* Read the raster data.  Here we just transpose it from the GIF array
 * to the Raster array, turning it from a series of blocks into one long
 * data stream, which makes life much easier for ReadCode().
 */

    ptr1 = Raster;
    do {
	ch = ch1 = NEXTBYTE;
	while (ch--) *ptr1++ = NEXTBYTE;
	if ((ptr1 - Raster) > filesize)
	    fprintf(stderr, "Corrupt GIF file (unblock)\n");
    } while(ch1);

    free(RawGIF);		/* We're done with the raw data now... */



/*EJB*/
    pixels = (unsigned char *)malloc(Width * Height);
    if (pixels == NULL)
    {
	fprintf(stderr, "Cannot allocate space for bitmap\n");
    }


/* Decompress the file, continuing until you see the GIF EOF code.
 * One obvious enhancement is to add checking for corrupt files here.
 */

    Code = ReadCode();
    while (Code != EOFCode) {

/* Clear code sets everything back to its initial value, then reads the
 * immediately subsequent code as uncompressed data.
 */

	if (Code == ClearCode) {
	    CodeSize = InitCodeSize;
	    MaxCode = (1 << CodeSize);
	    ReadMask = MaxCode - 1;
	    FreeCode = FirstFree;
	    CurCode = OldCode = Code = ReadCode();
	    FinChar = CurCode & BitMask;
	    AddToPixel(FinChar);
	}
	else {

/* If not a clear code, then must be data: save same as CurCode and InCode */

	    CurCode = InCode = Code;

/* If greater or equal to FreeCode, not in the hash table yet;
 * repeat the last character decoded
 */

	    if (CurCode >= FreeCode) {
		CurCode = OldCode;
		OutCode[OutCount++] = FinChar;
	    }

/* Unless this code is raw data, pursue the chain pointed to by CurCode
 * through the hash table to its end; each code in the chain puts its
 * associated output code on the output queue.
 */

	    while (CurCode > BitMask) {
		if (OutCount > 1024)
		    fprintf(stderr,
			"Corrupt GIF file (OutCount)\n");
		OutCode[OutCount++] = Suffix[CurCode];
		CurCode = Prefix[CurCode];
	    }

/* The last code in the chain is treated as raw data. */

	    FinChar = CurCode & BitMask;
	    OutCode[OutCount++] = FinChar;

/* Now we put the data out to the Output routine.
 * It's been stacked LIFO, so deal with it that way...
 */

	    for (i = OutCount - 1; i >= 0; i--)
		AddToPixel(OutCode[i]);
	    OutCount = 0;

/* Build the hash table on-the-fly. No table is stored in the file. */

	    Prefix[FreeCode] = OldCode;
	    Suffix[FreeCode] = FinChar;
	    OldCode = InCode;

/* Point to the next slot in the table.  If we exceed the current
 * MaxCode value, increment the code size unless it's already 12.  If it
 * is, do nothing: the next code decompressed better be CLEAR
 */

	    FreeCode++;
	    if (FreeCode >= MaxCode) {
		if (CodeSize < 12) {
		    CodeSize++;
		    MaxCode *= 2;
		    ReadMask = (1 << CodeSize) - 1;
		}
	    }
	}
	Code = ReadCode();
    }

    free(Raster);

/*EJB*/
	*w = Width;
	*h = Height;
	scale = 256;
	for (i=0; i<ColorMapSize; i++)
	{
		colrs[i].red = Red[i];
		colrs[i].green = Green[i];
		colrs[i].blue = Blue[i];
	}
	for (i=ColorMapSize; i<256; i++)
	{
		colrs[i].red = 0;
		colrs[i].green = 0;
		colrs[i].blue = 0;
	}

	bitp = pixels;
	for (i=0; i<((*w) * (*h)); i++)
	{
		if ((int)*bitp > (scale - 1))
			*bitp = (unsigned char)0;
		bitp++;
	}

	return(pixels);


}


/* Fetch the next code from the raster data stream.  The codes can be
 * any length from 3 to 12 bits, packed into 8-bit bytes, so we have to
 * maintain our location in the Raster array as a BIT Offset.  We compute
 * the byte Offset into the raster array by dividing this by 8, pick up
 * three bytes, compute the bit Offset into our 24-bit chunk, shift to
 * bring the desired code to the bottom, then mask it off and return it. 
 */
ReadCode()
{
int RawCode, ByteOffset;

    ByteOffset = BitOffset / 8;
    RawCode = Raster[ByteOffset] + (0x100 * Raster[ByteOffset + 1]);
    if (CodeSize >= 8)
	RawCode += (0x10000 * Raster[ByteOffset + 2]);
    RawCode >>= (BitOffset % 8);
    BitOffset += CodeSize;
    return(RawCode & ReadMask);
}


AddToPixel(Index)
unsigned char Index;
{
/*EJB*/
unsigned char *ptr;
ptr = (unsigned char *)(pixels + (Width * YC) + XC);
*ptr = Index;

/* Update the X-coordinate, and if it overflows, update the Y-coordinate */

    if (++XC == Width) {

/* If a non-interlaced picture, just increment YC to the next scan line. 
 * If it's interlaced, deal with the interlace as described in the GIF
 * spec.  Put the decoded scan line out to the screen if we haven't gone
 * past the bottom of it
 */

	XC = 0;
	if (!Interlace) YC++;
	else {
	    switch (Pass) {
		case 0:
		    YC += 8;
		    if (YC >= Height) {
			Pass++;
			YC = 4;
		    }
		break;
		case 1:
		    YC += 8;
		    if (YC >= Height) {
			Pass++;
			YC = 2;
		    }
		break;
		case 2:
		    YC += 4;
		    if (YC >= Height) {
			Pass++;
			YC = 1;
		    }
		break;
		case 3:
		    YC += 2;
		break;
		default:
		fprintf(stderr, "can't happen\n");
	    }
	}
    }
}
