BMPLoader.cpp

/*BMPLoader - loads Microsoft .bmp format
    Copyright (C) 2006  Chris Backhouse

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License along
    with this program; if not, write to the Free Software Foundation, Inc.,
    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.


  cjbackhouse@hotmail.com 		www.backhouse.tk
  
  I would appreciate it if anyone using this in something cool would tell me
  so I can see where it ends up.

  Takes a filename, returns an array of RGB pixel data
  Loads:
  24bit bitmaps
  256 colour bitmaps
  16 colour bitmaps
  2 colour bitmaps  (Thanks to Charles Rabier)

  This code is designed for use in openGL programs, so bitmaps not correctly padded will not
  load properly, I believe this only applies to: 
  256cols if width is not a multiple of 4
  16cols if width is not a multiple of 8
  2cols if width is not a multiple of 32

  Sample code:

	BMPClass bmp;
	BMPLoad(fname,bmp);
	glTexImage2D(GL_TEXTURE_2D,0,3,bmp.width,bmp.height,0,GL_RGB,GL_UNSIGNED_BYTE,bmp.bytes);
*/


#include "BMPLoader.h"

BMPClass::BMPClass(){bytes=0;}
BMPClass::~BMPClass(){delete[] bytes;}
BYTE& BMPClass::pixel(int x,int y,int c){return bytes[(y*width+x)*3+c];}
void BMPClass::allocateMem(){delete[] bytes;bytes=new BYTE[width*height*3];}

std::string TranslateBMPError(BMPError err)
{
	switch(err)
	{
	case(BMPNOTABITMAP):
		return "This file is not a bitmap, specifically it doesn't start 'BM'";
	case(BMPNOOPEN):
		return "Failed to open the file, suspect it doesn't exist";
	case(BMPFILEERROR):
		return "ferror said we had an error. This error seems to not always mean anything, try ignoring it";
	case(BMPBADINT):
		return "sizeof(int)!=4 quite a lot of rewriting probably needs to be done on the code";
	case(BMPNOERROR):
		return "No errors detected";
	case(BMPUNKNOWNFORMAT):
		return "Unknown bmp format, ie not 24bit, 256,16 or 2 colour";
	default:
		return "Not a valid error code";
	}
}

BMPError BMPLoad(std::string fname,BMPClass& bmp)
{
	if(sizeof(int)!=4) return BMPBADINT;
		
	FILE* f=fopen(fname.c_str(),"rb");		//open for reading in binary mode
	if(!f) return BMPNOOPEN;
	char header[54];
	fread(header,54,1,f);			//read the 54bit main header

	if(header[0]!='B' || header[1]!='M') 
	{
		fclose(f);
		return BMPNOTABITMAP;		//all bitmaps should start "BM"
	}

	//it seems gimp sometimes makes its headers small, so we have to do this. hence all the fseeks
	int offset=*(unsigned int*)(header+10);
	
	bmp.width=*(int*)(header+18);
	bmp.height=*(int*)(header+22);
	//now the bitmap knows how big it is it can allocate its memory
	bmp.allocateMem();

	int bits=int(header[28]);		//colourdepth

	int x,y,c;
	BYTE cols[256*4];				//colourtable
	switch(bits)
	{
	case(24):
		fseek(f,offset,SEEK_SET);
		fread(bmp.bytes,bmp.width*bmp.height*3,1,f);	//24bit is easy
		for(x=0;x<bmp.width*bmp.height*3;x+=3)			//except the format is BGR, grr
		{
			BYTE temp=bmp.bytes[x];
			bmp.bytes[x]=bmp.bytes[x+2];
			bmp.bytes[x+2]=temp;
		}
		break;

	case(8):
		fread(cols,256*4,1,f);							//read colortable
		fseek(f,offset,SEEK_SET);
		for(y=0;y<bmp.height;++y)						//(Notice 4bytes/col for some reason)
			for(x=0;x<bmp.width;++x)
			{
				BYTE byte;			
				fread(&byte,1,1,f);						//just read byte					
				for(int c=0;c<3;++c)
					bmp.pixel(x,y,c)=cols[byte*4+2-c];	//and look up in the table
			}
		break;

	case(4):
		fread(cols,16*4,1,f);
		fseek(f,offset,SEEK_SET);
		for(y=0;y<256;++y)
			for(x=0;x<256;x+=2)
			{
				BYTE byte;
				fread(&byte,1,1,f);						//as above, but need to exract two
				for(c=0;c<3;++c)						//pixels from each byte
					bmp.pixel(x,y,c)=cols[byte/16*4+2-c];
				for(c=0;c<3;++c)
					bmp.pixel(x+1,y,c)=cols[byte%16*4+2-c];
			}
		break;

	case(1):
		fread(cols,8,1,f);
		fseek(f,offset,SEEK_SET);
		for(y=0;y<bmp.height;++y)
			for(x=0;x<bmp.width;x+=8)
			{
				BYTE byte;
				fread(&byte,1,1,f);
				//Every byte is eight pixels
				//so I'm shifting the byte to the relevant position, then masking out
				//all but the lowest bit in order to get the index into the colourtable.
				for(int x2=0;x2<8;++x2)
					for(int c=0;c<3;++c)
						bmp.pixel(x+x2,y,c)=cols[((byte>>(7-x2))&1)*4+2-c];
			}
		break;

	default:
		fclose(f);
		return BMPUNKNOWNFORMAT;
	}

	if(ferror(f))
	{
		fclose(f);
		return BMPFILEERROR;
	}
	
	fclose(f);

	return BMPNOERROR;
}

BMPError BMPLoad(std::string fname){BMPClass bmp;return BMPLoad(fname,bmp);}

#ifdef __gl_h
BMPError BMPLoadGL(std::string fname)
{
	BMPClass bmp;
	BMPError e=BMPLoad(fname,bmp);
	if(e!=BMPNOERROR) return e;
		
	glEnable(GL_TEXTURE_2D);
	glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
	glTexImage2D(GL_TEXTURE_2D,0,3,bmp.width,bmp.height,0,GL_RGB,GL_UNSIGNED_BYTE,bmp.bytes);

	return BMPNOERROR;
}
#endif