Creating a png-file out of a SDL surface

[Oromis]

How to create a png-file out of a SDL surface? Searching this site and google didn't gave me an answer.

[helios]

SDL has a function that prepares an in-memory BMP (there's also a macro that calls this function and saves the BMP). You can pass this to any of the image libraries available. There's libpng, ImageMagick, FreeImage...

[Oromis]

Thanks for the reply.

So I'll need an image library. Do you recommend one? And what is this function? If you could show how it is done with a sample-code, or post a link where it's explained, that would be great.

[helios]

SDL_SaveBMP(screen,filename);
That's an example of the macro. The macro is declared like this:

#define SDL_SaveBMP(surface, file) \
		SDL_SaveBMP_RW(surface, SDL_RWFromFile(file, "wb"), 1) 

In case you don't know, an SDL_RWops abstracts some type of storage. It can linked to a file, a portion of memory, and not-sure-what-else.

I've used FreeImage with good results. It supports many formats and includes some useful algorithms (Lanczos is one of my favorites). It can be a bit difficult to get the hang of at first, but if you follow the examples you'll get it.

[Oromis]

Thanks helios.

This more complicated as I hoped it would be :). I thought the file would just contain a serie of numbers (the RGB-values or something like that), and then it would be quit easy to store those values into a file.
I don't know SDL quit wel yet, so I'll concentrate on that for now. I'll come back to this later, and learn about image libraries etc. Thanks for your help!

[helios]

What you said is true for BMP, but not for PNG. PNG images are compressed using a lossless algorithm (unlike JPEG which are compressed using a lossy algorithm).

Unless you have a very specific requirement for space, I'd recommend you stick you BMPs and SDL_SaveBMP().

[Oromis]

Oke, thanks! In that case, I'll stick to BMP for now. I need this to create files I'll use in other SDL applications, and because I'm always using png-images, I asked how to do. But this will work fine for me to.