[SDL] SDL_RWFromFile & IMG_LoadTyped_RW - 2 times

[Tyler Montbriand]

On June 18, 2005 07:40 am, Talie wrote:
> Hello !
>
> In my game, I pre-load all frames.  I use the function:
>    file_image = SDL_RWFromFile ("test.jpg", "rw");
> With this function, I have many pointers to files loaded in memory.
The files are NOT loaded into memory.  They're still on disk.  An SDL_RWops is 
not necessarly a memory block, or even necessarily a file -- it's just an 
abstraction that lets you read from lots of different things the same way.  
Once you load an image IMG_Load or whatever, *then* they're loaded into 
memory.

> Later in the game, I use the file in memory... so, I use:
>     the_image = IMG_LoadTyped_RW (file_image,0,"JPG");
Any particular reason you need IMG_LoadTyped_RW?  Nothing wrong with it, I 
just tend to use IMG_Load_RW since it can detect and load many different file 
formats, not just jpg.

> It works OK.  But, if later, I want to display again the same jpg file,
> with the same function:
>     the_image = IMG_LoadTyped_RW (file_image,0,"JPG");
Unless you freed the_image you loaded earlier with SDL_FreeSurface(the_image), 
it's still in memory!  Your program will leak memory like a screen door in a 
spaceship, waste massive amounts of CPU time, and thrash the hard disk by 
repeatedly loading images.  If all you're doing is loading from files, I 
think a better idea would be to just call IMG_Load("test.jpg") once, then 
repeatedly use the surface pointers it gives you.

Incidentally, the image probably fails to load the second time because the 
SDL_RWops stream was at the end of the file.  an SDL_RWops stream doesn't 
necessarily hold anything -- it's just an abstraction on some sort of stream.