bmptotexture.cpp

#include <stdio.h>

#define VERBOSE		false

#define BMP_MAGIC_NUMBER	0x4d42
#ifndef BI_RGB
#define BI_RGB			0
#define BI_RLE8			1
#define BI_RLE4			2
#endif


// bmp file header:
struct bmfh
{
	short bfType;		// BMP_MAGIC_NUMBER = "BM"
	int bfSize;		// size of this file in bytes
	short bfReserved1;
	short bfReserved2;
	int bfOffBytes;		// # bytes to get to the start of the per-pixel data
} FileHeader;

// bmp info header:
struct bmih
{
	int biSize;		// info header size, should be 40
	int biWidth;		// image width
	int biHeight;		// image height
	short biPlanes;		// #color planes, should be 1
	short biBitCount;	// #bits/pixel, should be 1, 4, 8, 16, 24, 32
	int biCompression;	// BI_RGB, BI_RLE4, BI_RLE8
	int biSizeImage;
	int biXPixelsPerMeter;
	int biYPixelsPerMeter;
	int biClrUsed;		// # colors in the palette
	int biClrImportant;
} InfoHeader;

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


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



// read a BMP file into a Texture:

unsigned char *
BmpToTexture( char *filename, int *width, int *height )
{
	FILE* fp;
#ifdef _WIN32
        errno_t err = fopen_s( &fp, filename, "rb" );
        if( err != 0 )
        {
		fprintf( stderr, "Cannot open Bmp file '%s'\n", filename );
		return NULL;
        }
#else
	fp = fopen( filename, "rb" );
	if( fp == NULL )
	{
		fprintf( stderr, "Cannot open Bmp file '%s'\n", filename );
		return NULL;
	}
#endif

	FileHeader.bfType = ReadShort( fp );


	// if bfType is not BMP_MAGIC_NUMBER, the file is not a bmp:

	if( VERBOSE ) fprintf( stderr, "FileHeader.bfType = 0x%0x = \"%c%c\"\n",
			FileHeader.bfType, FileHeader.bfType&0xff, (FileHeader.bfType>>8)&0xff );
	if( FileHeader.bfType != BMP_MAGIC_NUMBER )
	{
		fprintf( stderr, "Wrong type of file: 0x%0x\n", FileHeader.bfType );
		fclose( fp );
		return NULL;
	}


	FileHeader.bfSize = ReadInt( fp );
	if( VERBOSE )	fprintf( stderr, "FileHeader.bfSize = %d\n", FileHeader.bfSize );

	FileHeader.bfReserved1 = ReadShort( fp );
	FileHeader.bfReserved2 = ReadShort( fp );

	FileHeader.bfOffBytes = ReadInt( fp );
	if( VERBOSE )	fprintf( stderr, "FileHeader.bfOffBytes = %d\n", FileHeader.bfOffBytes );


	InfoHeader.biSize = ReadInt( fp );
	if( VERBOSE )	fprintf( stderr, "InfoHeader.biSize = %d\n", InfoHeader.biSize );
	InfoHeader.biWidth = ReadInt( fp );
	if( VERBOSE )	fprintf( stderr, "InfoHeader.biWidth = %d\n", InfoHeader.biWidth );
	InfoHeader.biHeight = ReadInt( fp );
	if( VERBOSE )	fprintf( stderr, "InfoHeader.biHeight = %d\n", InfoHeader.biHeight );

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

	InfoHeader.biPlanes = ReadShort( fp );
	if( VERBOSE )	fprintf( stderr, "InfoHeader.biPlanes = %d\n", InfoHeader.biPlanes );

	InfoHeader.biBitCount = ReadShort( fp );
	if( VERBOSE )	fprintf( stderr, "InfoHeader.biBitCount = %d\n", InfoHeader.biBitCount );

	InfoHeader.biCompression = ReadInt( fp );
	if( VERBOSE )	fprintf( stderr, "InfoHeader.biCompression = %d\n", InfoHeader.biCompression );

	InfoHeader.biSizeImage = ReadInt( fp );
	if( VERBOSE )	fprintf( stderr, "InfoHeader.biSizeImage = %d\n", InfoHeader.biSizeImage );

	InfoHeader.biXPixelsPerMeter = ReadInt( fp );
	InfoHeader.biYPixelsPerMeter = ReadInt( fp );

	InfoHeader.biClrUsed = ReadInt( fp );
	if( VERBOSE )	fprintf( stderr, "InfoHeader.biClrUsed = %d\n", InfoHeader.biClrUsed );

	InfoHeader.biClrImportant = ReadInt( fp );


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


	// pixels will be stored bottom-to-top, left-to-right:
	unsigned char *texture = new unsigned char[ 3 * nums * numt ];
	if( texture == NULL )
	{
		fprintf( stderr, "Cannot allocate the texture array!\n" );
		return NULL;
	}


	// extra padding bytes:

	int requiredRowSizeInBytes = 4 * ( ( InfoHeader.biBitCount*InfoHeader.biWidth + 31 ) / 32 );
	if( VERBOSE )	fprintf( stderr, "requiredRowSizeInBytes = %d\n", requiredRowSizeInBytes );

	int myRowSizeInBytes = ( InfoHeader.biBitCount*InfoHeader.biWidth + 7 ) / 8;
	if( VERBOSE )	fprintf( stderr, "myRowSizeInBytes = %d\n", myRowSizeInBytes );

	int oldNumExtra =  4*(( (3*InfoHeader.biWidth)+3)/4) - 3*InfoHeader.biWidth;
	if( VERBOSE )	fprintf( stderr, "Old NumExtra padding = %d\n", oldNumExtra );

	int numExtra = requiredRowSizeInBytes - myRowSizeInBytes;
	if( VERBOSE )	fprintf( stderr, "New NumExtra padding = %d\n", numExtra );



	

	// we can handle 24 bits of direct color:
	if( InfoHeader.biBitCount == 24 )
	{
		// 24-bit does not want to see the compression bits set:

		if (InfoHeader.biCompression != 0)
		{
			fprintf(stderr, "Wrong type of image compression: %d\n", InfoHeader.biCompression);
			fclose(fp);
			return NULL;
		}
		rewind( fp );
		fseek( fp, FileHeader.bfOffBytes, SEEK_SET );
		unsigned char *tp = texture;
		for( int t = 0; t < numt; t++ )
		{
			for( int s = 0; s < nums; s++, tp += 3 )
			{
				*(tp+2) = fgetc( fp );		// b
				*(tp+1) = fgetc( fp );		// g
				*(tp+0) = fgetc( fp );		// r
			}

			for( int e = 0; e < numExtra; e++ )
			{
				(void)fgetc( fp );
			}
		}
	}

	// we can also handle 8 bits of indirect color:
	if (InfoHeader.biBitCount == 8 && InfoHeader.biClrUsed == 256)
	{
		// 8-bit does not want to see the compression bits set:

		if (InfoHeader.biCompression != 0)
		{
			fprintf(stderr, "Wrong type of image compression: %d\n", InfoHeader.biCompression);
			fclose(fp);
			return NULL;
		}
		struct rgba32
		{
			unsigned char r, g, b, a;
		};
		struct rgba32* colorTable = new struct rgba32[InfoHeader.biClrUsed];

		rewind(fp);
		fseek(fp, sizeof(struct bmfh) + InfoHeader.biSize - 2, SEEK_SET);
		for (int c = 0; c < InfoHeader.biClrUsed; c++)
		{
			colorTable[c].b = fgetc(fp);
			colorTable[c].g = fgetc(fp);
			colorTable[c].r = fgetc(fp);
			colorTable[c].a = fgetc(fp);
			if (VERBOSE)	fprintf(stderr, "%4d:\t0x%02x\t0x%02x\t0x%02x\t0x%02x\n",
				c, colorTable[c].r, colorTable[c].g, colorTable[c].b, colorTable[c].a);
		}

		rewind(fp);
		fseek(fp, FileHeader.bfOffBytes, SEEK_SET);
		unsigned char* tp = texture;
		for (int t = 0; t < numt; t++)
		{
			for (int s = 0; s < nums; s++)
			{
				int index = fgetc(fp);
				*(tp + 0) = colorTable[index].r;	// r
				*(tp + 1) = colorTable[index].g;	// g
				*(tp + 2) = colorTable[index].b;	// b
				tp += 3;
			}

			for (int e = 0; e < numExtra; e++)
			{
				(void)fgetc(fp);
			}
		}

		delete[] colorTable;
	}

	// we can handle 32 bits of direct color:
	if (InfoHeader.biBitCount == 32)
	{
		// 32-bit doesn't mind if the compression bits are set -- we just ignore them:
		rewind( fp );
		fseek( fp, FileHeader.bfOffBytes, SEEK_SET );
		//numextra = 4 * (((4 * InfoHeader.biWidth) + 3) / 4) - 4 * InfoHeader.biWidth;
		unsigned char* tp = texture;
		for (int t = 0; t < numt; t++)
		{
			for (int s = 0; s < nums; s++, tp += 3)
			{
				*(tp+2) = fgetc(fp);		// b
				*(tp+1) = fgetc(fp);		// g
				*(tp+0) = fgetc(fp);		// r
				(void)fgetc(fp);
			}

			for (int e = 0; e < numExtra; e++)
			{
				(void)fgetc(fp);
			}
		}
	}


	fclose( fp );

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