Thread: need help with TGA writer.

I'm working on a TGA writer for a ray-tracer, but I can't get it to work. Can anyone see what is wrong with it?

Code:

#include <fstream.h>
#include <iostream.h>

typedef unsigned char UCHAR;
typedef signed char SCHAR;
typedef unsigned short int USINT;

class TARGA
{
public:
	TARGA();
	UCHAR idfield_no;		// no. of chars in id field.
	UCHAR colormap_type;	// 1 = map 0 = no map
	UCHAR image_type;		// 1 = color mapped, 2 = rgb, 3 = b&w. All uncompressed
	USINT colormap_origin;	// index of first entry (lo-hi)
	USINT colormap_length;	// no. of color map entries  (lo-hi)
	UCHAR colormap_bit;		// 16 for 16bit, 24 for 24bit...
	USINT x_origin;			// lower left corner (lo-hi)
	USINT y_origin;			// lower left corner (lo-hi)
	USINT width;			// width of image (lo-hi)
	USINT height;			// height of image (lo-hi)
	UCHAR pixel_bit;		// 16 for 16bit, 24 for 24bit...
	UCHAR img_descriptor;	// Wierd bit-thingy (ignore?)
	//UCHAR* idfield;		// Usually omitted (idfield_no=0)
	//UCHAR* colormap;		// Omitted if truecolor
	UCHAR* image_data;		// data stored differently depending on bitrate and colormap etc.
							// The footer is ignored
};
TARGA::TARGA()
{
	idfield_no	= 0;	
	colormap_type	= 0;	
	image_type 	= 2;		// truecolor
	colormap_origin = 0;
	colormap_length = 0;
	colormap_bit 	= 24;	// 24 bit
	x_origin	= 0;	
	y_origin	= 0;	
	width		= 2;		// width
	height		= 2;		// height
	pixel_bit	= 24;		// 24 bit
	img_descriptor	= 0;
	//idfield; omitted!	
	//colormap; omitted!	
	image_data = new UCHAR[width*height*3];

	for (int n=0; n<width*height*3; n++)
	{
		image_data[n]= 128; // should make all pixels gray
	}
}	


main(int argc, char* argv)
{
	fstream file;
	TARGA targa;
	
	char outfile[] = "outfile.tga";

	file.open(outfile, ios::out);	// should it be "ios::binary"?
	if (!file)
	{
		cout << "Error in opening " << outfile << " for writing" << endl;
		return 1;
	}

	file.write((UCHAR *)&targa,sizeof(targa));
	file.close();

	file.open(outfile, ios::in);
	if (!file)
	{
		cout << "Error in opening " << outfile << " for reading" << endl;
		return 1;
	}

	char c;
	int n=0;
	while (true)
	{
		file.get(c);
		cout << n << ": " << int(c) << endl;

		if (file.eof()) { break; }
		
		n++;
	}
	//file.read((UCHAR *)&targa,sizeof(targa));
	file.close();


	return 0;
}

The written file is wierd, as one can see from the output. Why, for example, are there values in the written file that were not in the object targa?

Some bytes of the file seems to be correct while others are not. For example the forth byte, is "-52" (or something) when it should be "0' (colormap origin). Or is that because it is a USINT?

Any suggestions?

>should it be "ios::binary"?

Yep.

You should create a method in your class to write each field to a file individually (or overload the << operator).

When classes/structs are written to a file directly any alignment padding will also get written (your first three fields (each one byte long) will probably get padded to four bytes so that the following integer (colormap_origin) falls on a double word boundary which is why your values are out), and any pointers that get written will just be the pointers and not the values that they point to.