Using the Zig build system to ease Windows compilation.

[arrufat]

As mentioned in #2652 (comment), creating a build.zig file to compile dlib would help reduce the number of bug reports and issues open due to people not being able to install dlib.

I have already started and you can follow the progress here.

It's still very raw, but it can already compile dlib and this simple example:

#include <dlib/image_io.h>
using rgb_image = dlib::matrix<dlib::rgb_pixel>;
int main(int argc, char** argv) {
    if (argc < 2) return 1;
    rgb_image image;
    dlib::load_image(image, argv[1]);
    dlib::save_jpeg(image, "image.jpg");
    dlib::save_png(image, "image.png");
}

All you need to do is add this at the end of the build.zig file:

// this function is already in the build.zig file
pub fn build(b: *std.build.Builder) void {

//  rest of the body

    const exe = b.addExecutable(.{
        .name = "image",
        .target = target,
        .optimize = optimize,
    });
    exe.addCSourceFile("main.cpp", &.{
        "-DDLIB_PNG_SUPPORT=1",
        "-DDLIB_JPEG_SUPPORT=1",
    });
    exe.linkLibrary(dlib);
    b.installArtifact(exe);
}

The whole steps look like

1. Download the latest Zig nightly from https://ziglang.org/download/
2. Decompress the file somewhere
3. Use my dlib branch: https://github.com/arrufat/dlib/tree/zig-build
4. Type: path/to/the/binary/zig build
5. Done!

If you added those lines to the build.zig file, you'll have an image executable in zig-out/bin/ that will read an image from the first argument and save a PNG and a JPEG version.

I've also seen that, on Windows, Zig can target MSVC: https://github.com/adamserafini/zaml/blob/main/builder.py#L21.

So, it should be possible to build the Python module on Windows targeting MSVC.
I will keep developing this when I have free time :)

I haven't managed to use the compiled libdlib.a with clang or gcc, apparently I don't know how to pass linker flags properly.
Here's what I am doing, in case someone can spot the mistake:

g++ -DDLIB_PNG_SUPPORT=1 -DDLIB_JPEG_SUPPORT=1 main.cpp -Izig-out/include -Lzig-out/lib -lz -lpng -ldlib

[arrufat]

Good news: I know how to pass linker flags properly.
The problem is, since I built with those dependencies with Zig, I need to build the executable with Zig as well:

zig c++ -DDLIB_PNG_SUPPORT=1 -DDLIB_JPEG_SUPPORT=1 main.cpp -Izig-out/include -Lzig-out/lib -lz -lpng -ljpeg -ldlib

[pfeatherstone]

It looks like the Zig build is similar to Meson

[pfeatherstone]

That's just one thing though. I don't know if coroutines, ranges and other 20 bits are in clang yet.

[arrufat]

So, that's why I'd like to try to make a build.zig for dlib.
If I manage to build the python module targeting the MSVC ABI, users won't need to install CMake, or Visual Studio, or anything like that on Windows, and we will avoid countless bug reports.

[arrufat]

I don't think I'll ever use the build.zig, but it's a good way to learn how to use their build system.

[pfeatherstone]

Amazing stuff. C++ should definitely have a master build tool that encapsulates compilers for different targets, build system and project configuration stuff. Zig seems to be very close. But I would prefer python as the build language to be honest.

[pfeatherstone]

Need to try SCons