bmptotexture.cpp

//
// Produced by Professor Mike Bailey at Oregon State University, from 2019
//

#include <stdio.h>

int	ReadInt( FILE * );
short	ReadShort( FILE * );


struct bmfh
{
	short bfType;
	int bfSize;
	short bfReserved1;
	short bfReserved2;
	int bfOffBits;
} FileHeader;

struct bmih
{
	int biSize;
	int biWidth;
	int biHeight;
	short biPlanes;
	short biBitCount;
	int biCompression;
	int biSizeImage;
	int biXPelsPerMeter;
	int biYPelsPerMeter;
	int biClrUsed;
	int biClrImportant;
} InfoHeader;

const int birgb = { 0 };



/**
 ** read a BMP file into a Texture:
 **/

unsigned char *
BmpToTexture( char *filename, int *width, int *height )
{

	int s, t, e;		// counters
	int numextra;		// # extra bytes each line in the file is padded with
	FILE *fp;
	unsigned char *texture;
	int nums, numt;
	unsigned char *tp;


	fp = fopen( filename, "rb" );
	if( fp == NULL )
	{
		fprintf( stderr, "Cannot open Bmp file '%s'\n", filename );
		return NULL;
	}

	FileHeader.bfType = ReadShort( fp );


	// if bfType is not 0x4d42, the file is not a bmp:

	if( FileHeader.bfType != 0x4d42 )
	{
		fprintf( stderr, "Wrong type of file: 0x%0x\n", FileHeader.bfType );
		fclose( fp );
		return NULL;
	}


	FileHeader.bfSize = ReadInt( fp );
	FileHeader.bfReserved1 = ReadShort( fp );
	FileHeader.bfReserved2 = ReadShort( fp );
	FileHeader.bfOffBits = ReadInt( fp );


	InfoHeader.biSize = ReadInt( fp );
	InfoHeader.biWidth = ReadInt( fp );
	InfoHeader.biHeight = ReadInt( fp );

	nums = InfoHeader.biWidth;
	numt = InfoHeader.biHeight;

	InfoHeader.biPlanes = ReadShort( fp );
	InfoHeader.biBitCount = ReadShort( fp );
	InfoHeader.biCompression = ReadInt( fp );
	InfoHeader.biSizeImage = ReadInt( fp );
	InfoHeader.biXPelsPerMeter = ReadInt( fp );
	InfoHeader.biYPelsPerMeter = ReadInt( fp );
	InfoHeader.biClrUsed = ReadInt( fp );
	InfoHeader.biClrImportant = ReadInt( fp );


	// fprintf( stderr, "Image size found: %d x %d\n", ImageWidth, ImageHeight );


	texture = new unsigned char[ 3 * nums * numt ];
	if( texture == NULL )
	{
		fprintf( stderr, "Cannot allocate the texture array!\b" );
		return NULL;
	}


	// extra padding bytes:

	numextra =  4*(( (3*InfoHeader.biWidth)+3)/4) - 3*InfoHeader.biWidth;


	// we do not support compression:

	if( InfoHeader.biCompression != birgb )
	{
		fprintf( stderr, "Wrong type of image compression: %d\n", InfoHeader.biCompression );
		fclose( fp );
		return NULL;
	}



	rewind( fp );
	fseek( fp, 14+40, SEEK_SET );

	if( InfoHeader.biBitCount == 24 )
	{
		for( t = 0, tp = texture; t < numt; t++ )
		{
			for( s = 0; s < nums; s++, tp += 3 )
			{
				*(tp+2) = fgetc( fp );		// b
				*(tp+1) = fgetc( fp );		// g
				*(tp+0) = fgetc( fp );		// r
			}

			for( e = 0; e < numextra; e++ )
			{
				fgetc( fp );
			}
		}
	}

	fclose( fp );

	*width = nums;
	*height = numt;
	return texture;
}



int
ReadInt( FILE *fp )
{
	unsigned char b3, b2, b1, b0;
	b0 = fgetc( fp );
	b1 = fgetc( fp );
	b2 = fgetc( fp );
	b3 = fgetc( fp );
	return ( b3 << 24 )  |  ( b2 << 16 )  |  ( b1 << 8 )  |  b0;
}


short
ReadShort( FILE *fp )
{
	unsigned char b1, b0;
	b0 = fgetc( fp );
	b1 = fgetc( fp );
	return ( b1 << 8 )  |  b0;
}