sdl .raw image-based map loading

elvee · 09-08-2004, 10:50 PM

Hi! I am attempting to make an destructable terrain demo using sdl. I made the maps using gimp and saved as .pnm in raw format. Right now the program loaded the images, and using pixel functions, it draws the image. The problem is that it doesnt turn out right. At all. Using 2 test maps, 1 (a 640x480 map) turns out somewhat familiar (but not at all right), and a 60x40 map is totally wrong.

here are screen shots to demonstrate the results:
640x480 map
60x40 map
*the application is DeterraGen. The results are in the deterragen window, and the map is in the gimp window
** the first image isn't completely up to date. The current one will not rotate the image, however it still looks the same (the interlace look that only shows about 1/4 of the picture)

Here is my image loading and printing functions, as well as my pixel function (pixel function from a tutorial, so if it looks familiar, thats why)

Code:

int map::load( const char* path )
{	
	unsigned long wloaded = 0, hloaded = 0;		
	ifstream mapfile(path, ios::binary );
	if( !mapfile )
	{
		return 0;
	}
	mapfile.ignore(255, '\n' );
	mapfile.ignore(255, '\n' );
	mapfile>> width >> height;
	cout<<"width: "<<width<<" height: "<<height<<endl;
	data = new terrain*[width];
	cout<<"map data pointer array initilized.\n";
	for(int i = 0; i< height; i++)
		data[i] = new terrain[width];
	mapfile.ignore(255, '\n' );
	for( int y = 0; y<height; y++)
	{
		for( int x = 0; x<width; x++ )
		{
			char buffer;
			buffer = mapfile.get();
			if( (unsigned short) buffer == 0 ) data[y][x].exists = 0;
			else 
			{
				data[y][x].exists = 1;
			}
			if( wloaded==0 )hloaded++;
		}
		wloaded++;
	}
	cout<<wloaded<<"x"<<hloaded<<" loaded.\n";
	mapfile.close();
	return 1;
}
void map::display( SDL_Surface *screen )
{
#ifdef DEBUG
	cout<<sizeof(terrain)<<endl;
	unsigned short hprinted =0, wprinted =0;
#endif
	for( int y = 0; y < height; y++ )
	{
		for( int x = 0; x < width; x++ )		
		{
//		cout<<x+1<<", "<<y+1<<": "<<data[x][y].exists<<endl;

			if( data[y][x].exists )
			{
				drawPixel( screen, x, y, 255, 255, 255 );
			}
			else  if( !data[y][x].exists )
			{
				drawPixel( screen, x, y, 0, 0, 0 );
			}
#ifdef DEBUG
			if(wprinted==0) hprinted++;
#endif
		}
#ifdef DEBUG
		wprinted++;
#endif
	}
#ifdef DEBUG
	cout<<wprinted<<"x"<<hprinted<<" printed.\n";
#endif
}

Code:

void drawPixel ( SDL_Surface *screen, int x, int y, Uint8 R, Uint8 G, Uint8 B )
{
	if( SDL_MUSTLOCK( screen ) ) SDL_LockSurface( screen );
	
	Uint32 color = SDL_MapRGB(screen->format, R, G, B);
	switch (screen->format->BytesPerPixel)
	{
		case 1: // Assuming 8-bpp
		{
			Uint8 *bufp;
			bufp = (Uint8 *)screen->pixels + y*screen->pitch + x;
			*bufp = color;
		}
		break;
		case 2: // Probably 15-bpp or 16-bpp
		{
			Uint16 *bufp;
			bufp = (Uint16 *)screen->pixels + y*screen->pitch/2 + x;
			*bufp = color;
		}
		break;
		case 3: // Slow 24-bpp mode, usually not used
		{
			Uint8 *bufp;
			bufp = (Uint8 *)screen->pixels + y*screen->pitch + x * 3;
			if(SDL_BYTEORDER == SDL_LIL_ENDIAN)
			{
				bufp[0] = color;					
				bufp[1] = color >> 8;
				bufp[2] = color >> 16;
			} else 
			{
				bufp[2] = color;
				bufp[1] = color >> 8;
				bufp[0] = color >> 16;
			}
		}
		break;
		case 4: // Probably 32-bpp
		{
			Uint32 *bufp;
			bufp = (Uint32 *)screen->pixels + y*screen->pitch/4 + x;
			*bufp = color;
		}
		break;
	}
	if( SDL_MUSTLOCK( screen ) ) SDL_UnlockSurface( screen );
}

I have spent many hours on this, and it has been VERY frustrating. Can anyone see why the weird results are produced? Can anyone help me fix it?

elvee · 09-09-2004, 11:25 PM

anyone?

dixy · 10-09-2004, 02:03 AM

Assuming that your image has the same pixel format like the screen surface you could easely use the following code:

SDL_Surface * loadsurface(char* filename) {
FILE *foo;
void *pixels;
SDL_Surface *loader;
int width;
int height;
int depth;
int pitch;
Uint32 Rmask;
Uint32 Gmask;
Uint32 Bmask;
Uint32 Amask;

foo = fopen(filename, "r");
fread((void *) &width, sizeof(int), 1, foo);
fread((void *) &height, sizeof(int), 1, foo);
cout<<"\n"<<width<<" "<<height;
pixels = (void *) new char(width*height*4);
fread(pixels, width*4, height, foo);
fclose(foo);
loader = SDL_CreateRGBSurfaceFrom(pixels, width, height, screen->format->BytesPerPixel, screen->pitch
, screen->format->Rmask, screen->format->Gmask, screen->format->Bmask, screen->format->Amask);
return loader;
}

void savesurface(SDL_Surface *pic, char *filename) {
FILE *foo;
foo = fopen(filename, "w+");
fwrite((void *) &pic->w, sizeof(pic->w), 1, foo);
fwrite((void *) &pic->h, sizeof(pic->h), 1, foo);
fwrite(pic->pixels, pic->w*pic->format->BytesPerPixel, pic->h, foo);
fclose(foo);
}

To make your image use the same pixel format the screen has:
temp = SDL_DisplayFormat(screen);

I wish you success.

And don't use fstream, ofstream and ifstream in writing binary data. You'll get them corrupt even if you use open(filename, ios::binary);
If you don't believe me try this:
ofstream foo;
ifstream bar;
char b[100];
int n;
double f;

foo = open("file.data", ios::binary);
foo<<"Hello world!\n"<<175<<12356.4325;
foo.close();

bar = open("file.data", ios::binary);
bar>>b;
bar>>n;
bar>>f;
bar.close();
cout<<"\n"<<b<<n<<f;

What did u see?U can even use bar.get(b,13);bar>>n;bar>>f;

Take a look to the "binary" file file.data. Open it with a text editor. How do u see the int number and the double number written in the file?They appear like binary data?No, they were written like text data even if you used ios::binary flag.