Displaying GIF Graphic Files In C

/**************************************************************************** ** This support Compuserve 256 colour GIF87a and GIF89a image up to ** ** 320x200 in size. ** ****************************************************************************/ //This program requires a stack of at least 19.5K!! #include "stdio.h" typedef struct GIFHeader { char Signature [7]; unsigned int ScreenWidth, ScreenHeight; unsigned char Depth, Background, Zero; }; struct GIFDescriptor { char Separator; unsigned int ImageLeft, ImageTop, ImageWidth, ImageHeight; unsigned char Depth; }; char far *Screen = (char far *)0xA0000000L; //For loading from the file FILE *GIFFile; unsigned int BPointer; unsigned char Buffer [257]; //GIF data is stored in blocks of a certain size unsigned char BlockSize; //For loading the code unsigned char CodeSize; char BitsIn; unsigned char Temp; //Coordinates unsigned int X, Y, tlX, tlY, brX, brY; //The string table unsigned int Prefix [4096]; unsigned char Suffix [4096]; //This sets the display to VGA 320x200 in 256 colours void VGAScreen () { asm { mov ax, 0x13 int 0x10 } } //This resets the display to text mode void TextScreen () { asm { mov ax, 0x3 int 0x10 } } //This sets a DAC register to a specific Red Green Blue-value void SetDAC(unsigned char DAC, unsigned char R, unsigned char G, unsigned char B) { outportb (0x3C8, DAC); outportb (0x3C9, R); outportb (0x3C9, G); outportb (0x3C9, B); } //This sets one pixel on the screen void PutPixel (unsigned int x, unsigned int y, unsigned char c) { Screen [(y << 8) + (y << 6) + x] = c; } //Function to read from the buffer unsigned char LoadByte () { //Read next block} if (BPointer == BlockSize) { fread (Buffer, BlockSize + 1, 1, GIFFile); BPointer = 0; } //Return byte return Buffer [BPointer++]; } //Procedure to read the next code from the file unsigned int ReadCode () { int Counter; unsigned int Code; Code = 0; //Read the code, bit by bit for (Counter = 0; Counter < CodeSize; Counter++) { //Maybe, a new byte needs to be loaded with a further 8 bits if (++BitsIn == 9) { Temp = LoadByte (); BitsIn = 1; } //Add the current bit to the code if (Temp & 1) Code += 1 << Counter; Temp >>= 1; } return Code; } //Procedure to draw a pixel void NextPixel (unsigned int c) { //Actually draw the pixel on screen PutPixel (X, Y, c & 255); //Move to next row, if necessary if (++X == brX) { X = tlX; Y++; } } //Local function to output a string. Returns the first character. unsigned char OutString (unsigned int CurCode) { unsigned int OutCount; unsigned char OutCode [1024]; //If it's a single character, output that if (CurCode < 256) { NextPixel (CurCode); } else { OutCount = 0; //Store the string, which ends up in reverse order do { OutCode [OutCount++] = Suffix [CurCode]; CurCode = Prefix [CurCode]; } while (CurCode > 255); //Add the last character OutCode [OutCount++] = CurCode; //Output all the string, in the correct order do { NextPixel (OutCode [--OutCount]); } while (OutCount); } //Return 1st character return CurCode; } //This actually loads the GIF void LoadGIF (char *Filename) { //For loading from the GIF file struct GIFHeader Header; struct GIFDescriptor Descriptor; //Colour information unsigned char BitsPerPixel, NumOfColours; unsigned int DAC; unsigned char Palette [256][3]; //For indexing the string table unsigned int FirstFree, FreeCode; //All the code information unsigned char InitCodeSize; unsigned int Code, OldCode, MaxCode; //Special codes unsigned int ClearCode, EOICode; //Check whether the GIF file exists, and open it GIFFile = fopen (Filename, "rb"); if (GIFFile == 0) { TextScreen (); printf ("Could not open file %s", Filename); return; } //Read header fread (&Header, 6, 1, GIFFile); Header.Signature [6] = 0; fread (&Header.ScreenWidth, sizeof (Header) - 7, 1, GIFFile); //Check signature and terminator if ((strcmp (Header.Signature, "GIF87a") && strcmp (Header.Signature, "GIF89a")) || Header.Zero) { TextScreen (); printf ("Not a valid GIF file\n"); return; } //Get amount of colours in image BitsPerPixel = 1 + (Header.Depth & 7); NumOfColours = (1 << BitsPerPixel) - 1; //Load global colour map fread (Palette, 3, (NumOfColours + 1), GIFFile); for (DAC = 0; DAC <= NumOfColours; DAC++) SetDAC (DAC, Palette [DAC][0] >> 2, Palette [DAC][1] >> 2, Palette [DAC][2] >> 2); //Load the image descriptor fread (&Descriptor, sizeof (Descriptor), 1, GIFFile); if (Descriptor.Separator != ',') { TextScreen (); printf ("Incorrect image descriptor.\n"); return; } //Get image corner coordinates tlX = Descriptor.ImageLeft; tlY = Descriptor.ImageTop; brX = tlX + Descriptor.ImageWidth; brY = tlY + Descriptor.ImageHeight; //Some restrictions apply if (Descriptor.Depth & 128) { TextScreen (); printf ("Local colour maps not supported\n"); return; } if (Descriptor.Depth & 64) { TextScreen (); printf ("Interlaced images not supported\n"); return; } //Get initial code size fread (&CodeSize, 1, 1, GIFFile); //GIF data is stored in blocks, so it's necessary to know the size fread (&BlockSize, 1, 1, GIFFile); //Start loader BPointer = BlockSize; //Special codes used in the GIF spec ClearCode = 1 << CodeSize; //Code to reset EOICode = ClearCode + 1; //End of file //Initialize the string table FirstFree = ClearCode + 2; //Strings start here FreeCode = FirstFree; //Strings can be added here //Initial size of the code and its maximum value InitCodeSize = ++CodeSize; MaxCode = 1 << CodeSize; BitsIn = 8; //Start at top left of image X = Descriptor.ImageLeft; Y = Descriptor.ImageTop; do { //Read next code Code = ReadCode (); //If it's an End-Of-Information code, stop processing if (Code == EOICode) break; //If it's a clear code... else if (Code == ClearCode) { //Clear the string table FreeCode = FirstFree; //Set the code size to initial values CodeSize = InitCodeSize; MaxCode = 1 << CodeSize; //The next code may be read Code = ReadCode (); OldCode = Code; //Set pixel NextPixel (Code); //Other codes } else { /*If the code is already in the string table, it's string is displayed, and the old string followed by the new string's first character is added to the string table.*/ if (Code < FreeCode) Suffix [FreeCode] = OutString (Code); else { /*If it is not already in the string table, the old string followed by the old string's first character is added to the string table and displayed.*/ Suffix [FreeCode] = OutString (OldCode); NextPixel (Suffix [FreeCode]); } //Finish adding to string table Prefix [FreeCode++] = OldCode; //If the code size needs to be adjusted, do so if (FreeCode >= MaxCode && CodeSize < 12) { CodeSize++; MaxCode <<= 1; } //The current code is now old OldCode = Code; } } while (Code != EOICode); //Close the GIF file fclose (GIFFile); } void main (int argcount, char *argvalue[]) { char FileName [80]; //Check if a filename was passed as a parameter, otherwise ask for one if (argcount > 1) { strcpy (FileName, argvalue [1]); } else { printf ("Enter filename:"); gets (FileName); } //Switch to graphics screen VGAScreen (); //Load GIF file LoadGIF (FileName); //Wait for keypress getch (); //Switch back to text mode TextScreen (); }