Plugin System – an alternative to GetProcAddress and interfaces

// BMPParser.cpp - a very simple BMP file parser
//
// Part of the Plugin System tutorial
//
///////////////////////////////////////////////////////////////////////////////

#include <windows.h>
#include <stdio.h>
#include "..\ImageParser.h"

// CBMPParser implements the IImageParser interface
class CBMPParser: public IImageParser
{
public:
	virtual HBITMAP ParseFile( const char *fname );
	virtual bool SupportsType( const char *type ) const;

private:
	HBITMAP CreateBitmap( int width, int height, void **data );
};

// Creates a bitmap with the specified size
HBITMAP CBMPParser::CreateBitmap( int width, int height, void **data )
{
	BITMAPINFO bmi={sizeof(BITMAPINFOHEADER),width,height,1,24,0,0,0,0,0,0};
	return CreateDIBSection(NULL,&bmi,DIB_RGB_COLORS,data,0,0);
}

// Parses a BMP file
HBITMAP CBMPParser::ParseFile( const char *fname )
{
	FILE *f=fopen(fname,"rb");
	if (!f) return NULL;

	BITMAPFILEHEADER bmfh;
	memset(&bmfh,0,sizeof(bmfh));
	fread(&bmfh,sizeof(bmfh),1,f);
	BITMAPINFOHEADER bmih;
	memset(&bmih,0,sizeof(bmih));
	fread(&bmih,sizeof(bmih),1,f);
	int width=bmih.biWidth;
	int height=bmih.biHeight;

	if (bmih.biBitCount!=24) {
		// only 24 bit images are supported
		fclose(f);
		return NULL;
	}

	// create the HBITMAP
	void *data;
	HBITMAP bitmap=CreateBitmap(width,height,&data);
	if (!bitmap) {
		fclose(f);
		return NULL;
	}

	// read the pixels
	int pitch=(width*3+3)&~3;
	fread(data,pitch,height,f);

	fclose(f);
	return bitmap;
}

// Notifies the host that the plugin supports the BMP type
bool CBMPParser::SupportsType( const char *type ) const
{
	return stricmp(type,".bmp")==0;
}

static CBMPParser g_BMPParser;

// The host calls this function to get access to the image parser
extern "C" __declspec(dllexport) IImageParser *GetParser( void ) { return &g_BMPParser; }