Fix psd load error on windows

[fabiencastan]

On windows, ifstream::open does not guarantee to be at the beginning of
the file.

[lgritz]

Really? What are the circumstances in which something else happens?

[lgritz]

LGTM, by the way, I'm just curious about what's really going on here.

Also, do you need this backported to any release branches, or only the master?

[fabiencastan]

Really? What are the circumstances in which something else happens?

No idea ! Just systematically reads values from anywhere when I load a psd on windows...

Also, do you need this backported to any release branches, or only the master?

Only master.
Thanks

[c42f]

Yikes, this one makes me uncomfortable. The behaviour that

std::ifstream file("blah")

reads from the beginning seems like very basic and important standard behaviour. Reading section 27.9.1.4 of the C++ standard http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3376.pdf says that the underlying filebuf is opened as if by calling fopen() with mode "rb".

I too wonder what's really going on here...

[lgritz]

I'm uncomfortable with the weirdness of this, I'm worried we're just masking another problem.

Do you have a specific PSD file that can reproduce the problem? (Can you send it to me? Or does it have this problem for all PSD files?)

I think you should try this: instead of seeking, try instead checking and printing the current file position :

streampos pos = m_file.tellg();
if (pos != 0)
    std::cerr << "Weird, current position is " << pos << "\n";

Let us know what it prints. And if it never prints anything at all, then perhaps this is not the problem.

[fabiencastan]

It's not specific to one psd file.

See the streampos before and after the manual seekg to 0.
http://static.inky.ws/image/2800/image.jpg

[fabiencastan]

Does that answer your question?

[lgritz]

Sorry, the image appears to have no size for me. Can you just cut and paste the text?

[fabiencastan]

Can't use your code directly as std::streampos is an implementation defined class.

//////////////////////////////////////////////////////
// ... m_file.open...
std::streampos pos1 = m_file.tellg();
m_file.seekg( 0, std::ios::beg );
std::streampos pos2 = m_file.tellg();
// ... load_header...
//////////////////////////////////////////////////////

Debug values:

pos1._Stz == 0
pos1._Myoff == -1
pos1._Fpos == 0
pos1._Mystate == 0

pos2._Stz == 0
pos2._Myoff == 0
pos2._Fpos == 0
pos2._Mystate == 0

[lgritz]

This patch is no longer necessary, since we have added the seek() to Filesystem::open, it happens automatically on Windows. Closing.