Shaderc system library FFI, building, and linking
This crate contains the lower-level C interface for the Shaderc library.
For the higher-level Rust-friendly interface, please see the
[shaderc](https://docs.rs/shaderc) crate.
The [Shaderc](https://github.com/google/shaderc) library provides an API
for compiling GLSL/HLSL source code to SPIRV modules. It has been shipping
in the Android NDK since version r12b.
This crate contains Rust FFI inteface to the Shaderc library. It also
handles system library detection and building from source if no system
library installed via `build.rs`.
The order of preference in which the build script will attempt to obtain
Shaderc can be controlled by several options:
1. The option `--features build-from-source` will prevent automatic library
detection and force building from source.
2. If the `SHADERC_LIB_DIR` environment variable is set to
`/path/to/shaderc/libs/`, it will take precedence and
`libshaderc_combined.a` (and the glslang and SPIRV libraries on Linux)
will be searched in the `/path/to/shaderc/libs/` directory.
3. On Linux, `/usr/lib/` will be automatically searched for system libraries
if none of the above were given.
4. If no other option was set or succeeded, shaderc-sys will fall back to
checking out and compiling a copy of Shaderc. This procedure is quite
slow.
The build script also tries to check whether [Ninja](https://ninja-build.org/)
is available on `PATH`. Ninja is required to build with Visual Studio because
MSBuild does not support paths longer than MAX_PATH. On other platforms,
Ninja is optional but is generally faster than the default build tool.