C/C++ - Loading Bitmap Files (Manually)

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This is how you maually load a bmp file

The bitmap file format:
Bitmap file header
Bitmap info header
palette data
Bitmap Dada

so on with the code part, this is our struct we need to create to hold the bitmap file header

typedef struct tagBITMAPFILEHEADER
{
WORD bfType;  //specifies the file type
DWORD bfSize;  //specifies the size in bytes of the bitmap file
WORD bfReserved1;  //reserved; must be 0
WORD bfReserved2;  //reserved; must be 0
DWORD bOffBits;  //species the offset in bytes from the bitmapfileheader to the bitmap bits
}BITMAPFILEHEADER;

the bftype field checks to see if you are infact loading a bmp file, and if you are the field should be 0x4D42.

Now we need to create our bitmapinfoheader struct. This holds info about our bitmap(self explainitory).

typedef struct tagBITMAPINFOHEADER
{
DWORD biSize;  //specifies the number of bytes required by the struct
LONG biWidth;  //specifies width in pixels
LONG biHeight;  //species height in pixels
WORD biPlanes; //specifies the number of color planes, must be 1
WORD biBitCount; //specifies the number of bit per pixel
DWORD biCompression;//spcifies the type of compression
DWORD biSizeImage;  //size of image in bytes
LONG biXPelsPerMeter;  //number of pixels per meter in x axis
LONG biYPelsPerMeter;  //number of pixels per meter in y axis
DWORD biClrUsed;  //number of colors used by th ebitmap
DWORD biClrImportant;  //number of colors that are important
}BITMAPINFOHEADER;

Now on to loading our Bitmap

unsigned char *LoadBitmapFile(char *filename, BITMAPINFOHEADER *bitmapInfoHeader)

FILE *filePtr; //our file pointer
BITMAPFILEHEADER bitmapFileHeader; //our bitmap file header
unsigned char *bitmapImage;  //store image data
int imageIdx=0;  //image index counter
unsigned char tempRGB;  //our swap variable

//open filename in read binary mode
filePtr = fopen(filename,"rb");
if (filePtr == NULL)
return NULL;

//read the bitmap file header
fread(&bitmapFileHeader, sizeof(BITMAPFILEHEADER,1,filePtr);

//verify that this is a bmp file by check bitmap id
if (bitmapFileHeader.bfType !=0x4D42)
{
fclose(filePtr);
return NULL;
}

//read the bitmap info header
fread(bitmapInfoHeader, sizeof(BITMAPINFOHEADER),1,filePtr);

//move file point to the begging of bitmap data
fseek(filePtr, bitmapFileHeader.bfOffBits, SEEK_SET);

//allocate enough memory for the bitmap image data
bitmapImage = (unsigned char*)malloc(bitmapInfoHeader->biSizeImage);

//verify memory allocation
if (!bitmapImage)
{
free(bitmapImage);
fclose(filePtr);
return NULL;
}

//read in the bitmap image data
fread(bitmapImage,bitmapInfoHeader->biSizeImage,filePtr);

//make sure bitmap image data was read
if (bitmapImage == NULL)
{
fclose(filePtr);
return NULL;
}

//swap the r and b values to get RGB (bitmap is BGR)
for (imageIdx = 0,imageIdx < bitmapInfoHeader->biSizeImage;imageIdx+=3)
{
tempRGB = bitmapImage[imageIdx];
bitmapImage[imageIdx] = bitmapImage[imageIdx + 2];
bitmapImage[imageIdx + 2] = tempRGB;
}

//close file and return bitmap iamge data
fclose(filePtr);
return bitmapImage;
}

Now to make use of all of this:

BITMAPINFOHEADER bitmapInfoHeader;
unsigned char *bitmapData;
...
bitmapData = LoadBitmapFile("mypic.bmp",&bitmapInfoHeader);
//now do what you want with it, later on i will show you how to display it in a normal window

Later on ill put up Writing a to bmp and how to load a targa file and how to display them.