Support raw formats on windows

[til-schneider]

Reading raw camera formats is currently only supported on macOS and Linux - not on Windows.

The problem on Windows is that node-libraw doesn't compile on Windows. I forked node-libraw and tried some things but I didn't get it to work.

There is a compile error in the code of LibRaw (LibRaw is wrapped by node-libraw). Compiling LibRaw should generally be possible, since they provide downloads for Windows.

Here is the error (see full log):

c:\projects\ansel\node_modules\libraw\vendor\libraw\src\libraw_c_api.cpp(277): error C2491: 'libraw_set_demosaic': definition of dllimport function not allowed [C:\projects\ansel\node_modules\libraw\build\vendor\libraw.vcxproj]

According to Microsoft's description of error C2491, the code of LibRaw marks DLL imports the wrong way - see source code of libraw_c_api.cpp. So I wonder why the LibRaw-Team can build this on windows. I also tried to build node-libraw as static library, but this doesn't work either.

I'm a relative nowise when it comes to building C code. I don't know what else to do. So if anybody can help here - please go ahead.

[stefano-xy]

Try to add #define LIBRAW_LIBRARY_BUILD before the #include of libraw.h, without that it seems the DllDef macro is not expanded properly. If it works, please contribute it back to upstream.

Sorry I could not test it myself due to lack of time, I've just had a quick look at the upstream code.

[til-schneider]

Sorry for the long time not answering. I didn't have a Windows building environment all the time. Now I set one up and managed to try your hint.

Unfortunately it still doesn't build.

I still get the same error (I'm using LibRaw 0.19.5):

c:\users\til\workspace\picturama\submodules\node-libraw\vendor\libraw\src\libraw_c_api.cpp(277): error C2491: "libraw_set_demosaic": definition of dllimport function not allowed [C:\Users\Til\workspace\picturama\subm
odules\node-libraw\build\vendor\libraw.vcxproj]

[akjoshi]

FYI - I checked with Libraw team in github LibRaw/LibRaw#161 (comment) and the team has confirmed that it's build-able in windows using both Microsoft compiler and gcc (mingw32).

[til-schneider]

Thank you for asking the Libraw team. I already knew that Libraw itself builds on Windows. What I didn't get to work yet is building Libraw as node package (using gyp). But I'm no C expert and don't know what else to do. So if anyone can help here, please go ahead.

Maybe the hint from @LibRaw's comment can help:

[...] building without windows-specific memory mapped input stream is also possible

[akjoshi]

I submitted a pull request in node-libraw repo to support windows compilation.

m0g/node-libraw#8 (comment)

[rohrlaf]

Have you considered compiling LibRaw directly with WASM, which is Emscripten for C++: https://developer.mozilla.org/en-US/docs/WebAssembly/C_to_wasm

This could get rid of the additional layer provided by node-libraw and also offer performance improvements as it will be pre-compiled and optimised code to be executed.

Maybe this proof-of-concept might help as well: https://github.com/arbarlow/libraw-wasm-example

[til-schneider]

I'm not sure, whether checking out the pull request of @akjoshi or compiling LibRaw with WASM is the better way to go. In the end, performance is most important for Picturama (because it sucks if switching between photos is not fast).

@rohrlaf: Why do you think, performance would be better with WASM? My experience with Emscripten was the exact opposite. For HEIC/HEIF support, I ended up creating node-libheif, because using a native binding was 3x faster than using Emscripten.