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There is a gotcha I ran into when mixing SDL's openGL interface with direct openGL calls to glTexImage2D.

libsdl adjusts the state variables GL_UNPACK_ROW_LENGTH and GL_UNPACK_ALIGNMENT when converting pixel data in memory to textures inside the SDL_UpdateTexture function.

The trouble is, the library doesn't restore those to default values. Online searches for example code that makes use of glTexImage2D don't explicitly set those values, particularly GL_UNPACK_ROW_LENGTH. So when you cut and paste supposedly working code into your project, it won't work out of the box. Incorrect GL_UNPACK_ROW_LENGTH (which is default 0 in openGL's state) can cause seg faults, or at the very least textures will be skewed in some way.

The safe solution is to set GL_UNPACK_ROW_LENGTH and GL_UNPACK_ALIGNMENT to their default values before using glTexImage2D:
	glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
	glPixelStorei(GL_UNPACK_ALIGNMENT, 4);
or, set them to whatever is necessary at the time. It is unsafe to assume they are set to default values.

I don't think it's reasonable to expect libsdl to restore those variables to default values. This is just some detail programmers need to be aware of. I'm entering this as a bug because I'd like somewhere for there to be a warning about this issue in the libsdl documentation.

I wasted some time tracking down the cause of the problems I was experiencing, and had to examine the libsdl source to get a hint of what was going on. I had never made use of those GL_UNPACK_* variables, wasn't aware of their existence. Hopefully other people can benefit from my experience.