CODEWITHSUNDEEP
c++texturessdlsegmentation-fault
Arlington
Arlington

Reputation: 79

SDL2 SIGSEGV in creating texture from surface

I am trying to create an SDL_Texture using SDL_CreateTextureFromSurface. I have successfully implemented this function multiple times without issue. Currently I am getting the following backtrace information:

#0  0xb7ef1e80 in ?? () from /usr/lib/libSDL2-2.0.so.0
#1  0xb7edf19c in ?? () from /usr/lib/libSDL2-2.0.so.0
#2  0xb7f12e1d in ?? () from /usr/lib/libSDL2-2.0.so.0
#3  0xb7f13ee7 in ?? () from /usr/lib/libSDL2-2.0.so.0
#4  0xb7eb2c08 in ?? () from /usr/lib/libSDL2-2.0.so.0
#5  0xb7e9f474 in SDL_CreateTextureFromSurface () from /usr/lib/libSDL2-2.0.so.0
#6  0x0805999e in Building::draw (this=0xbfffe9a8, Render=@0xbffff6d8: 0x81bd1b8)
    at /code/directory/LIBRARY.h:194
#7  0x08063df7 in main (argc=1, args=0xbffffac4) at Program.cpp:1151

The only thing different between the rest of my code and this particular implementation is that my SDL_Surface is a pointer array defined as follows:

//<Initialize window and renderer (not included here)>
SDL_Surface** Surf;
SDL_Surface* SomeOtherSurface;
int SurfSize = 0;

SomeOtherSurface = LoadBMP("Filename.bmp");
for (i = 0; i < 2; i++)
{
    Surf = (SDL_Surface**) realloc(Surf,SurfSize+1)*sizeof(SDL_Surface*));

    SDL_LockSurface(SomeOtherSurface);
    Surf[i] = SDL_CreateRGBSurfaceFrom(SomeOtherSurface->pixels,SomeOtherSurface->w,SomeOtherSurface->h,32,SomeOtherSurface->pitch,0xFF000000,0x00FF0000,0x0000FF00,0x000000FF); //Create a surface in Surf based on SomeOtherSurface
    SDL_UnlockSurface(SomeOtherSurface);
    SurfSize++;
}
SDL_FreeSurface(SomeOtherSurface);
SDL_Texture* Tex1;
Tex1 = SDL_CreateTextureFromSurface(Render,Surf[0]); //Create the texture; this throws the SIGSEGV

I've written a similar code elsewhere in the program and it hasn't failed; can anyone figure out what's going wrong here? The error would seem to suggest a problem with the memory, but if I try to access Surf[0]->w it returns values as expected.

EDIT: Some additional info which could help solve this: In my code, I free the 'SomeOtherSurface' surface prior to defining the texture. If I define the texture prior to freeing the surface, everything works fine. Is it possible that the two surfaces are sharing the pixel data address?

SOLVED: I need to use SDL_BlitSurface to copy the data and modify it. If I then proceed to free the surface after using SDL_CreateRGBSurfaceFrom then the existing pixel data is also deleted resulting in a segfault when the program tries to access that memory address.

Upvotes: 0

Views: 534

Answers (1)

Arlington
Arlington

Reputation: 79

The issue with this code is that SDL_CreateRGBSurfaceFrom uses existing pixel data; thus, when you call an SDL_FreeSurface, the pixel data gets lost. Now, Surf[i] tries to find that pixel data when calling SDL_CreateTextureFromSurface and the memory is not accessible.

Solution: using an SDL_BlitSurface to make a copy of the pixel data for further use.

Upvotes: 1

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