Fix typos in SDL2 example

[AileenLumina]

I read through the OpenGL docs and I think I found a typo that caused the example to crash unless VSync fails. I believe this is not what you wanted. :p

[coveralls]

Coverage remained the same at 42.488% when pulling 382388f on hackofthewild:patch-1 into 427ead5 on swistakm:master.

[swistakm]

Weird. Are you sure this is correct? The official docs say that SDL_GL_SetSwapInterval() returns -1 if it fails (link).

Anyway, by crash you mean something unexpected like in #71 or just exit(1) and message from print? If it's the latter could you share full stdout? Maybe there is problem with VSync. I will try to reproduce this on my own box.

[AileenLumina]

Oh? Let me see.

[AileenLumina]

This is the output I get without fixing the typo:

Warning: Unable to set VSync! SDL Error:  b'wglSwapIntervalEXT(): The operation completed successfully.\r\n'

I forgot, I also had to fix another error that involved explicitly casting the bytes returned by SDL_GetError() to a str. Let me add that to this PR.

[swistakm]

Still, that would mean that SDL_GL_SetSwapInterval() failed and it seems odd to fail on normal VSync. I think we could try in that situation to retry with SDL_GL_SetSwapInterval(0) or maybe even do not bother with VSync or try all three options (-1, 1, 0) from the most preferable to the least preferable.

Really weird.

[AileenLumina]

I tried all three options, always the same "issue". It looks like a warning is printed when actually, things work correctly (The operation completed successfully.) due to incorrect interpretation of the exit code of the operation.

[swistakm]

This is exactly why I find it really weird :)

See src/video/windows/SDL_windowsopengl.c:

826-int
827-WIN_GL_SetSwapInterval(_THIS, int interval)
828-{
829-    if ((interval < 0) && (!_this->gl_data->HAS_WGL_EXT_swap_control_tear)) {
830-        return SDL_SetError("Negative swap interval unsupported in this GL");
831:    } else if (_this->gl_data->wglSwapIntervalEXT) {
832:        if (_this->gl_data->wglSwapIntervalEXT(interval) != TRUE) {
833:            return WIN_SetError("wglSwapIntervalEXT()");
834-        }
835-    } else {
836-        return SDL_Unsupported();
837-    }
838-    return 0;
839-}

and src/video/SDL_video.c:

3475-int
3476:SDL_GL_SetSwapInterval(int interval)
3477-{
3478-    if (!_this) {
3479-        return SDL_UninitializedVideo();
3480-    } else if (SDL_GL_GetCurrentContext() == NULL) {
3481-        return SDL_SetError("No OpenGL context has been made current");
3482-    } else if (_this->GL_SetSwapInterval) {
3483-        return _this->GL_SetSwapInterval(_this, interval);
3484-    } else {
3485-        return SDL_SetError("Setting the swap interval is not supported");
3486-    }
3487-}

[AileenLumina]

Looks like this was my device's fault. Not surprised, seeing as it is powered by an Intel Atom.

[swistakm]

Closing because it was really old issue.