/*- * 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 #include #ifdef SYSV #include #else /* SYSV */ #include #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 (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"); } } } }