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Is IMG_Load_RW freeing buffer created with new[] ?
sanitowi


Joined: 22 Jan 2015
Posts: 10
Post Posted: Sun Mar 22, 2015 8:58 pm
Hi, in some code I load images from a zip file via Physfs.

This Method loads the image from the zip file into a RWops
Code:

SDL_RWops* GameEngine::LoadFromZip(std::string target)
{
  // Archive is mounted in GameEngine::Init()

  // Check if target file is in archive
  if(PHYSFS_exists(target.c_str()) == 0)
  {
     // handle error
  }

  // Open target file
  PHYSFS_file *file = PHYSFS_openRead(target.c_str());
  if(file == nullptr)
  {
     // handle error
  }


  // Read target into memory
  PHYSFS_sint64 filesize = PHYSFS_fileLength(file);
  char *buffer = new char[filesize];
  if(PHYSFS_read(file, buffer, sizeof(char), filesize) != filesize)
  {
     // handle error
  }
  PHYSFS_close(file);


  // Create RWops
  SDL_RWops *rwops = SDL_RWFromMem(buffer, filesize);
  if(rwops == nullptr)
  {
     // handle error
  }

  // delete[] buffer;  // CRASH
  return rwops;
}


and the returned RWops is used in some functions to load create s Surface, Texture ect..
e.g.
Code:

SDL_Surface* GameEngine::LoadSurface(std::string filename)
{
  // Load image from memory
  SDL_RWops *rwops = LoadFromZip(filename);
  SDL_Surface *surface = IMG_Load_RW(rwops, 1);
  if(surface == nullptr)
  {
     // handle error
  }

  return surface;
}


I'm not sure what happens with the buffer allocated in the LoadFromZip Function.
Is it freed by

SDL_Surface *surface = IMG_Load_RW(rwops, 1);

?


The code works, but when I put a delete[] buffer just before the return of the LoadFromZip function,
the programm crashes.

What's the right way to do this, if I don't want to write the code of the LoadFromZip funtion in every function I use for loading
surfaces, textures, mix_chunks ect. from the zip file.

P.S.

I didn't post the error checkings in the code ... Wink
Is IMG_Load_RW freeing buffer created with new[] ?
Jonny D


Joined: 12 Sep 2009
Posts: 932
Post Posted: Sun Mar 22, 2015 11:04 pm
The rwops is only a handle for accessing the buffer data in a common way.  It does not keep an extra copy of the buffer, so if you delete the buffer before the rwops, then you're effectively pulling the rug out from under the rwops.  You will have to manually delete the buffer when you are all done with the rwops.

There's a PhysFS extension, physfsrwops, that you should use to avoid that extra buffer.  That might help your use case here.


Jonny D




On Sunday, March 22, 2015, sanitowi wrote:
Quote:
Hi, in some code I load images from a zip file via Physfs.

This Method loads the image from the zip file into a RWops



Code:


SDL_RWops* GameEngine::LoadFromZip(std::string target)
{
  // Archive is mounted in GameEngine::Init()

  // Check if target file is in archive
  if(PHYSFS_exists(target.c_str()) == 0)
  {
     // handle error
  }

  // Open target file
  PHYSFS_file *file = PHYSFS_openRead(target.c_str());
  if(file == nullptr)
  {
     // handle error
  }


  // Read target into memory
  PHYSFS_sint64 filesize = PHYSFS_fileLength(file);
  char *buffer = new char[filesize];
  if(PHYSFS_read(file, buffer, sizeof(char), filesize) != filesize)
  {
     // handle error
  }
  PHYSFS_close(file);


  // Create RWops
  SDL_RWops *rwops = SDL_RWFromMem(buffer, filesize);
  if(rwops == nullptr)
  {
     // handle error
  }

  // delete[] buffer;  // CRASH
  return rwops;
}





and the returned RWops is used in some functions to load create s Surface, Texture ect..
e.g.



Code:


SDL_Surface* GameEngine::LoadSurface(std::string filename)
{
  // Load image from memory
  SDL_RWops *rwops = LoadFromZip(filename);
  SDL_Surface *surface = IMG_Load_RW(rwops, 1);
  if(surface == nullptr)
  {
     // handle error
  }

  return surface;
}





I'm not sure what happens with the buffer allocated in the LoadFromZip Function.
Is it freed by

SDL_Surface *surface = IMG_Load_RW(rwops, 1);

?


The code works, but when I put a delete[] buffer just before the return of the LoadFromZip function,
the programm crashes.

What's the right way to do this, if I don't want to write the code of the LoadFromZip funtion in every function I use for loading
surfaces, textures, mix_chunks ect. from the zip file.

P.S.

I didn't post the error checkings in the code ... Wink

sanitowi


Joined: 22 Jan 2015
Posts: 10
Post Posted: Mon Mar 23, 2015 9:43 am
Thanks for your hint.
Are there some docs available for the physfsrwops extension?
I have not found any yet..

For now I use a std::vector as buffer in the LoadFromZip function, return a copy of it and create the rwops
in the calling function...
sanitowi


Joined: 22 Jan 2015
Posts: 10
Post Posted: Mon Mar 23, 2015 1:23 pm
Ok, I was able to get it working with physfsrwops,
but there are two little problems.

I opend another thread for that.
https://forums.libsdl.org/viewtopic.php?p=47383#47383