Plugin System – an alternative to GetProcAddress and interfaces

// TGAParser.cpp - a very simple TGA file parser
//
// Part of the Plugin System tutorial
//
///////////////////////////////////////////////////////////////////////////////

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

// CTGAParser implements the IImageParser interface
class CTGAParser: 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 CTGAParser::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 TGA file
HBITMAP CTGAParser::ParseFile( const char *fname )
{
	FILE *f=fopen(fname,"rb");
	if (!f) return NULL;

// Targa header structure
#pragma pack(push,1)
	struct TGAHeader
	{
		unsigned char idFieldLength;
		unsigned char colorMapType;
		unsigned char imageType;
		unsigned short firstColorMapEntry;
		unsigned short colorMapLength;
		unsigned char colorMapEntrySize;
		unsigned short xOrigin;
		unsigned short yOrigin;
		unsigned short width;
		unsigned short height;
		unsigned char bitsPerPixel;
		unsigned char descriptorBits;
	};
#pragma pack(pop)

	TGAHeader header;
	fread(&header,sizeof(header),1,f);

	int width=header.width;
	int height=header.height;

	if (header.imageType&8) {
		// compressed images are not supported
		fclose(f);
		return NULL;
	}
	if (header.bitsPerPixel!=24) {
		// only 24 bit images are supported
		fclose(f);
		return NULL;
	}

	// create the HBITMAP
	void *data;
	HBITMAP bitmap=CreateBitmap(width,(header.descriptorBits&32)?-height:height,&data);
	if (!bitmap) {
		fclose(f);
		return NULL;
	}

	// read the pixels
	int pitch=(width*3+3)&~3;
	char *ptr=(char*)data;
	fseek(f,ftell(f)+header.idFieldLength,SEEK_SET);
	for (int y=0;y<height;y++,ptr+=pitch)
		fread(ptr,width,3,f);

	fclose(f);
	return bitmap;
}

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

static CTGAParser g_TGAParser;

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