Replace rust-freetype with freetype-rs

[jdm]

freetype-rs looks so much more pleasant to use. We could get rid of lots of unsafe blocks in the font-related code in gfx, and probably fix some of those lurking crashes that appear every few months.

[jdm]

Note: NCSU students might be working on this, so please contact me before commencing any work to avoid overlap.

[kmcallister]

They submitted #4215, which switches to Piston's freetype-sys but not to the high level bindings.

This issue is up for grabs again and would be a great start for an eager contributor from the Rust community!

[schuster]

I'd like to work on this. What's the best way to test that this works, once I've made the change?

[jdm]

@schuster Likely just test some sites that use various fonts and check that they look the same before and after.

[bgdncz]

Any news on this?

[jdm]

@boghison You're welcome to start working on it if you'd like.

[schuster]

@boghison I'm working on it my free time now and then, but I haven't had nearly as much time as I'd like. Feel free to start on it, although I'm still going to work on it as well (as a Rust learning exercise for myself as much as anything else).

It should be pretty simple if you already know Rust; I'm just slowed down by learning about lifetimes, lifetime parameters, and other parts of the ownership model as I go through it all.

[bgdncz]

Ok, I am gonna give this a try :)

[bgdncz]

@jdm What I am worried about is FreeTypeLibraryHandle and its use, because AFAIU this relies on the raw implementation and therefore has to be entirely replaced. Thoughts?

[jdm]

@boghison I think it's fine to leave raw API when necessary - you can replace the FT_Library with the Library type (https://github.com/PistonDevelopers/freetype-rs/blob/master/src/library.rs#L34), but it looks like our use of FT_Memory and the UserPtr should stay, since we do special things with them.

[bgdncz]

@jdm Wouldn't it be better to reformat the code entirely, because my prediction is that this is just gonna end up a mess because of the mixing of unsafe code (using freetype_rs::ffi types) and the safe code (provided by the library). Is it still OK?

[jdm]

Well, your other option is to add the bits that are missing to freetype-rs - the code at http://mxr.mozilla.org/servo/source/components/gfx/platform/freetype/font_context.rs#115 is different than the code at https://github.com/PistonDevelopers/freetype-rs/blob/master/src/library.rs#L27, so we would need an API that allows us to provide our own allocation functions and user pointer when creating a Library. That would be a useful addition :)

[bgdncz]

@jdm So basically send code upstream? That would be the optimal solution IMHO. Getting rid of unsafe code in servo is the end result, I will start working on freetype-rs then :)

[jdm]

Thanks!

[bgdncz]

@jdm Question about Rust: can any function be marked as extern?

[jdm]

https://doc.rust-lang.org/nightly/reference.html#extern-functions suggests yes!

[bgdncz]

@jdm Great! Then consider that API done! Also, I was thinking this could be sent upstream. What do you think? (I am asking all those questions to get the facts right)

[jdm]

Makes sense, but it probably shouldn't include the pt_size and set_char_size call.

[bgdncz]

@jdm Actually I didn't notice, but there's a new_memory_face function in library.rs, which is almost the same thing.

I am trying to understand how servo handles fonts cross-platform and I see that FontHandle is where all the magic happens. It augments the bindings to the platform-dependent libs into a struct that has the same calls on all platforms, is that right? I need to know something: all possible calls are encapsulated in FontHandleMethods, correct? Because I have to understand what I can delete/change and what not (so for example I can edit the FontHandle impl, because it is platform-dependent and not used externally)

[jdm]

Good question! Yes, it appears that FontHandleMethods is the trait that encapsulates all cross-platform font API usage.

[bgdncz]

Awesome! I'll let you know if I have any more questions

[bgdncz]

@jdm What is stretchiness?

[jdm]

https://developer.mozilla.org/en-US/docs/Web/CSS/font-stretch

[bgdncz]

@jdm I have a problem:
native library freetype is being linked to by more than one package, and can only be linked to by one package

freetype-sys v0.1.2
freetype-sys v2.4.11 (https://github.com/servo/libfreetype2#3f22b9dd)

[jdm]

You probably need to remove the appropriate entries from http://mxr.mozilla.org/servo/source/components/gfx/Cargo.toml#79 .

[bgdncz]

@jdm I've updated those fields when I started. Maybe the problem lies in the fact that servo has dependencies which depend respectively on either freetype-sys (servo) or rust-freetype, but I can't deal with that.

[jdm]

I don't have any good ideas right now. If you push your changes to a branch (as well as your changes to freetype-rs), perhaps we can play with it.

[jdm]

Oh wait, Cargo.lock helped me figure out that https://github.com/servo/rust-azure/blob/master/Cargo.toml#L31is also using it.

[jdm]

As are skia and libfontconfig.

[bgdncz]

@jdm That is correct, because Cargo.lock is what I was basing my assumption on. Any thoughts?

[jdm]

Yeah, all of skia, libfontconfig and rust-azure should switch to using the same freetype-sys that freetype-rs uses: https://github.com/PistonDevelopers/freetype-rs/blob/master/Cargo.toml#L21

[jdm]

You can deal with them by cloning the repositories, making changes, and following http://doc.crates.io/guide.html#overriding-dependencies

[bgdncz]

@jdm In file included from libazure/mozilla/TypedEnumInternal.h:15:0,
from libazure/mozilla/TypedEnum.h:12,
from libazure/Types.h:10,
from libazure/2D.h:9,
from src/azure-c.cpp:6:
libazure/mozilla/Attributes.h:419:0: warning: "MOZ_WARN_UNUSED_RESULT" redefined

define MOZ_WARN_UNUSED_RESULT attribute ((warn_unused_result))

^
:0:0: note: this is the location of the previous definition
In file included from src/azure-c.cpp:6:0:
libazure/2D.h:32:22: fatal error: ft2build.h: No such file or directory
compilation terminated.

UPDATE: I fixed this by manually adding -I/usr/include/freetype2/ to CXXFLAGS in makefile.cargo.

[bgdncz]

@jdm What if we ship all the necessary files directly with rust-azure?

[bgdncz]

My code changes are here. Until the freetype-sys issue is solved, it's in limbo.

[nox]

What do we need to do here? WR depends on our freetype crate and I want to remove that.

[jdm]

We need to switch all of the packages that depend on freetype-sys away from it.

[nox]

@jdm I'm not sure I parse what you mean. Do you mean we should switch all the packages that depend on servo/rust-freetype away from it?

[jdm]

Yes, that's what I meant.