fix stbi__parse_png_file() reading too much bytes

[miniupnp]

just "rewind" the bytes that have been read past the IEND chunk.

should fix #360 and #524

[miniupnp]

@flowCRANE could you check if that fixes your issue ?

I added a couple of bytes at the end of a file and checked using ftell() that is is indeed rewinding the additional bytes ;)

I guess I should submit the patch to https://github.com/nothings/stb if it works for you

[flowCRANE]

If it works for you, it will work for me. You can test it on my sample file — test.files.zip (inside is sdl.dat file).

If you are able to open sdl.dat file and read two images from the stream successively, without any errors, in this way:

Stream := SDL_IOFromFile('sdl.dat', 'rb');

Image1 := IMG_LoadTexture_IO(Renderer, Stream, False);
Image2 := IMG_LoadTexture_IO(Renderer, Stream, False);

then it means that your fix is correct and solves the problem. And thanks so much for looking into this topic and finding the cause of the problems!

[miniupnp]

Some Pascal :)

@flowCRANE So you are not able to test the patch ?

[miniupnp]

With the following code, img2 is null without the patch and is not null with the patch.
So I guess it works.

{
	SDL_IOStream *src = SDL_IOFromFile("/home/nanard/code/git/SDL_image/sdl.dat", "rb");
	SDL_Texture *img1 = IMG_LoadTexture_IO(renderer, src, false);
	SDL_Texture *img2 = IMG_LoadTexture_IO(renderer, src, true);
        printf("src=%p img1=%p img2=%p\n", src, img1, img2);
}

[miniupnp]

nothings/stb#1751

[slouken]

Merged, thanks!

[flowCRANE]

@miniupnp: yeah, I'm in Free Pascal's camp and have no thought of betraying the colors. ;)

The main idea is that the data stream can be constructed in such a way that multiple PNG images can be written one after the other and that they can be loaded one after the other, like in the example above. This will mean that when the image is read, the pointer is in the correct place.

I haven't done extensive testing, so I don't know if the same problem exists for other formats. But I'll look into it and let you know if I find anything. Thanks again for the fix!

[sezero]

Merged, thanks!

Add to SDL2 branch too.

And also to SDL3 main repo?

[slouken]

Yep, done