CODEWITHSUNDEEP
c++sdl
KingKoopa
KingKoopa

Reputation: 99

How to use SDL functions like SDL_DestroyTexture() properly?

I am doing this lazyfoo SDL tutorial right now.

The render class they using has some image to texture function which is using SDL_Surface* and SDL_Texture. At the end of the function they "free" the created surface by calling SDL_FreeSurface().

Now, I am wondering:

  1. Why exactly i have to free the Surface at all (variables are local?)?
  2. Why its ok to let the created Texture be without calling SDL_DestroyTexture?
  3. What exacty does it mean when i destroy a texture or free a surface?
    bool Tile::loadTexture(const char* path){  
    SDL_Texture* newTexture = NULL;  
    SDL_Surface* loadedSurface = IMG_Load(path);  
    //...some code  
    Texture = newTexture;  
    SDL_FreeSurface(loadedSurface);         
    return Texture != NULL;}

Upvotes: 1

Views: 3722

Answers (1)

Nelfeal
Nelfeal

Reputation: 13269

Why exactly i have to free the Surface at all (variables are local?)?

The pointer loadedSurface is local. The actual surface isn't: there is something similar to malloc inside of IMG_Load. The same way you use free on memory allocated with malloc, you use SDL_FreeSurface on surfaces allocated with IMG_Load (or SDL_CreateRGBSurface and so on).

Why its ok to let the created Texture be without calling SDL_DestroyTexture?

SDL_DestroyTexture is called, inside of LTexture::free, which is called by the destructor of LTexture. So SDL_DestroyTexture is pretty much guaranteed to be called at some point if loadFromFile was called.

What exacty does it mean when i destroy a texture or free a surface?

It means the same thing as using free on memory allocated with malloc, or using delete on memory allocated with new, or calling std::unique_ptr::reset (without argument), and so on. Each variant does something sligthly different. If you want to know what exactly differs between SDL_DestroyTexture, SDL_FreeSurface, free, etc, you can look at the source code: SDL is open source and there are quite a few open source implementations of free out there.

Upvotes: 4

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