Displaying BMP Graphic Files in C

#include #include #ifdef __DJGPP #include #endif #ifdef __DJGPP char *Screen; #else char far *Screen; #endif //This sets the display to VGA 320x200 in 256 colours void VGAScreen () { union REGS r; r.h.ah = 0; r.h.al = 0x13; int86(0x10, &r, &r); } //This resets the display to text mode void TextScreen () { union REGS r; r.h.ah = 0; r.h.al = 0x3; int86(0x10, &r, &r); } //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 loads in the actual BMP-file and displays it. void LoadBMP (char *FileName) { //BMP Header structure struct BMPHeader { #ifdef __DJGPP unsigned short bfType __attribute__((packed)); long bfSize __attribute__((packed)); long bfReserved __attribute__((packed)); long bfOffBits __attribute__((packed)); long biSize __attribute__((packed)); long biWidth __attribute__((packed)); long biHeight __attribute__((packed)); unsigned short biPlanes __attribute__((packed)); unsigned short biBitCount __attribute__((packed)); long biCompression __attribute__((packed)); long biSizeImage __attribute__((packed)); long biXPelsPerMeter __attribute__((packed)); long biYPelsPerMeter __attribute__((packed)); long biClrUsed __attribute__((packed)); long biClrImportant __attribute__((packed)); #else unsigned short bfType; long bfSize, bfReserved, bfOffBits, biSize, biWidth, biHeight; unsigned short biPlanes, biBitCount; long biCompression, biSizeImage, biXPelsPerMeter, biYPelsPerMeter, biClrUsed, biClrImportant; #endif } Header; //File handle FILE *BMPFile; //Required for palette unsigned char c, Palette[256][4]; //USed for loading into video memory unsigned int offset, lines, paddedWidth; //Check to see whether the file exists and can be opened BMPFile = fopen (FileName, "rb"); if (BMPFile == NULL) { strcat (FileName,".BMP"); BMPFile = fopen (FileName, "rb"); if (BMPFile == NULL) { printf ("Couldn't open file."); return; } } //Read in header information fread (&Header, 54, 1, BMPFile); //Check to see whether we can display it if (Header.bfType != 19778 || Header.bfReserved != 0 || Header.biPlanes !=1) { //Not a valid bitmap file - don't display fclose (BMPFile); return; } if (Header.biCompression != 0) { //Compressed file - don't display fclose (BMPFile); return; } if (Header.biBitCount != 8) { //Other than 8-bit colour - don't display fclose (BMPFile); return; } if (Header.biWidth > 320 || Header.biHeight > 200) { //Too large - don't display fclose (BMPFile); return; } //Load in the palette fread (&Palette, 1024, 1, BMPFile); for (c = 0; c < 255; c++) { SetDAC (c, Palette[c][2] >> 2, Palette[c][1] >> 2, Palette[c][0] >> 2); } //Set appropriate position to display graphics data offset = (100 + (Header.biHeight >> 1)) * 320 + 160 - (Header.biWidth >> 1); //We've read no lines so far lines = 0; //Pad line length to 4bytes paddedWidth = Header.biWidth & 0xFFFC; if (Header.biWidth != paddedWidth) paddedWidth += 4; //Decode and display graphics while (lines < Header.biHeight) { //Read next line fread (Screen + offset, paddedWidth, 1, BMPFile); //Move up one line on the screen offset -= 320; //increase amount of lines read lines++; } fclose (BMPFile); } void main (int argcount, char *argvalue[]) { char FileName[80]; //Set up a pointer to the vga memory at A000:0000 #ifdef __DJGPP __djgpp_nearptr_enable (); Screen = (char *)(__djgpp_conventional_base + 0xA0000); #else Screen = (char far *)0xA0000000L; #endif if (argcount>1) { strcpy (FileName,argvalue[1]); } else { printf ("Enter filename:"); gets (FileName); } VGAScreen (); LoadBMP (FileName); getch (); TextScreen (); }