Return Value Consistency For Animation Decoder & Encoder

[LordOfXen]

As I have said I would make an issue for discussion regarding the return value of getting frames from our animation decoder.

Should we keep it this way or work on a more robust solution like an enum?
Most APIs returns a status rather than 0-1/boolean in such situations.

We can implement a similar status system both for decoder and encoder for symmetry.

Please let me know your thoughts.

[LordOfXen]

Example 1:

typedef Uint16 /* or just int */ coder_status;

EXTERN coder_status AddFrame(...) // for encoder

EXTERN coder_status GetFrame(...) // for decoder

[slouken]

It's a lot easier to just think in terms of boolean return values when using APIs, and practically speaking most people are just going to do this loop:

while (getnextframe(&frame)) {
    processframe(frame)
}

We solved this in the SDL IOStream system by adding a status field so you could check for EOF vs error. Maybe we should do something like that here, for the rare cases where the caller can do something useful with an error status vs a complete animation? e.g. IMG_GetAnimationDecoderStatus()

[LordOfXen]

Yeah, that makes sense. Rather than checking if SDL_GetError is empty or not, we can add IMG_GetAnimationDecoderStatus (and IMG_GetAnimationEncoderStatus maybe for symmetry?), hold the state value in our decoder/encoder struct, and return that in the function.

[LordOfXen]

To be continued in #611.