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Bug 4559 - SDL_SetVideoMode will fail when called twice if returned surface is freed with SDL_FreeSurface
Summary: SDL_SetVideoMode will fail when called twice if returned surface is freed wit...
Status: RESOLVED FIXED
Alias: None
Product: sdl12-compat
Classification: Unclassified
Component: everything (show other bugs)
Version: unspecified
Hardware: x86_64 Linux
: P2 normal
Assignee: Ryan C. Gordon
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2019-03-21 11:50 UTC by Dario
Modified: 2019-03-22 13:44 UTC (History)
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Description Dario 2019-03-21 11:50:31 UTC 
SDL_SetVideoMode(int,int,int,Uint32) returns a VideoSurface12 (SDL12_Surface *).
An application hold this pointer and call to SDL_FreeSurface(SDL12_Surface *).

A second call to SDL_SetVideo_Mode results in a segmentation fault because VideoSurface12 has been invalidated, is not NULL and will be accessed.

I can bypass this issue by adding a conditional on the SDL_FreeSurface that tests the SDL12_Surface pointer for equality against the VideoSurface12.

I encountered this problem while trying a game development engine called BennuGD (https://bitbucket.org/dacucar/bennugd/src/master/) which runs on SDL 1.2.

After doing my small hack, I was able to run a relatively complex game without much trouble.

If you need additional information, let me know.
Comment 1 Ryan C. Gordon 2019-03-21 15:15:19 UTC 
Ah, interesting...you aren't supposed to call SDL_FreeSurface() on the return value from SDL_SetVideoMode(), but I see that SDL 1.2 checks for this case and returns immediately if trying to free the screen surface.

I'll fix that.

--ryan.
Comment 2 Dario 2019-03-21 16:09:13 UTC 
Interesting, that is exactly what I did to solve it.

You are right in any case, I checked the SDL 1.2 documentation and it says the surface should not be freed. 

So I guess I will have to report that too to the other project :).

I can also advance that, when adding the VideoSurface12 check and returning on the SDL_FreeSurface I encountered that when switching from FullScreen to Windowed mode, the game was not correctly scaled: it is as if the game stayed "large" but the area was clipt to the size of the window screen.
Comment 3 Dario 2019-03-21 16:47:52 UTC 
Regarding the later, I will investigate further and report when I know more.
Comment 4 Ryan C. Gordon 2019-03-22 13:44:44 UTC 
> Regarding the later, I will investigate further and report when I know more.

Please do, and open a separate bug for it so we don't forget to fix it!  :)

As for this bug: fixed in https://hg.libsdl.org/sdl12-compat/rev/f4f3bf9e36e1, thanks!

--ryan.