gl-rs

An OpenGL function pointer loader for the Rust Programming Language.

Basic usage

The easiest way to use OpenGL is to simply include the gl crate.

To do so, add this to your Cargo.toml:

[dependencies.gl]
git = "https://github.com/bjz/gl-rs"

You can import the pointer style loader and type aliases like so:

extern crate gl;
// include the OpenGL type aliases
use gl::types::*;

You must load the function pointers into their respective function pointers using the load_with function. You must supply a loader function from your context library, This is how it would look using [glfw-rs] (https://github.com/bjz/glfw-rs):

// the supplied function must be of the type:
// `&fn(symbol: &str) -> Option<extern "C" fn()>`
// `window` is a glfw::Window
gl::load_with(|s| window.get_proc_address(s));

// loading a specific function pointer
gl::Viewport::load_with(|s| window.get_proc_address(s));

Calling a function that has not been loaded will result in a failure like: panic!("gl::Viewport was not loaded"), which avoids a segfault. This feature does not cause any run time overhead because the failing functions are assigned only when load_with is called.

// accessing an enum
gl::RED_BITS;

// calling a function
gl::DrawArrays(gl::TRIANGLES, 0, 3);

// functions that take pointers are unsafe
unsafe {  gl::ShaderSource(shader, 1, &c_str, std::ptr::null()) };

Each function pointer has an associated boolean value allowing you to check if a function has been loaded at run time. The function accesses a corresponding global boolean that is set when load_with is called, so there shouldn't be much overhead.

if gl::Viewport::is_loaded() {
    // do something...
}

Extra features

The global and struct generators will attempt to use fallbacks functions when they are available. For example, if glGenFramebuffers cannot be loaded it will also attempt to load glGenFramebuffersEXT as a fallback.

Using gl_generator

If you need a specific version of OpenGL, or you need a different API (OpenGL ES, EGL, WGL, GLX), or if you need certain extensions, you should use the gl_generator plugin instead.

See gfx_gl for an example of using a custom gfx-rs loader for a project.

Add this to your Cargo.toml:

[build-dependencies]
gl_generator = "*"

[dependencies]
gl_common = "*"

Under the [package] section, add:

build = "build.rs"

Create a build.rs to pull your specific version/API:

extern crate gl_generator;    // <-- this is your build dependency
extern crate khronos_api;    // included by gl_generator

use std::os;
use std::old_io::File;

fn main() {
    let dest = Path::new(os::getenv("OUT_DIR").unwrap());

    let mut file = File::create(&dest.join("gl_bindings.rs")).unwrap();

    // This generates bindsings for OpenGL ES v3.1
    gl_generator::generate_bindings(gl_generator::GlobalGenerator,
                                    gl_generator::registry::Ns::Gles2,
                                    khronos_api::GL_XML,
                                    vec![],
                                    "3.1", "core", &mut file).unwrap();
}

Then use it like this:

mod gles {
    include!(concat!(env!("OUT_DIR"), "/gl_bindings.rs"));
}

/*
 * Simple loading example
 */
fn main() {
    // Assuming window is GLFW, initialized, and made current
    gles::load_with(|s| window.get_proc_address(s));
}

The build.rs file will generate all the OpenGL functions in a file named, gl_bindings.rs plus all enumerations, and all types in the types submodule.

Arguments

The type of loader to generate. Can be gl_generator::StaticGenerator, gl_generator::StaticStructGenerator, gl_generator::StructGenerator, or gl_generator::GlobalGenerator.
The API to generate. Can be Gl, Gles1, Gles2 (GLES 2 or 3), Wgl, Glx, Egl.
The file which contains the bindings to parse. Can be GL_XML (for GL and GL ES), GLX_XML, WGL_XML, EGL_XML.
Extra extensions to include in the bindings. These are specified as a list of strings.
The requested API version. This is usually in the form "major.minor".
The GL profile. Can be either "core" or "compatibility". "core" will only include all functions supported by the requested version it self, while "compatibility" will include all the functions from previous versions as well.

Generator types

Global generator

The global generator is the one used by default by the gl crate. See above for more details.

Struct generator

The struct generator is a cleaner alternative to the global generator.

The main difference is that you must call gl::Gl::load_with instead of gl::load_with, and this functions returns a struct of type Gl. The OpenGL functions are not static functions but member functions in this Gl struct. This is important when the GL functions are associated with the current context, as is true on Windows.

The enumerations and types are still static and available in a similar way as in the global generator.

Static generator

The static generator generates plain old bindings. You don't need to load the functions.

This generator should only be used only if the platform you are compiling for is guaranteed to support the requested API. Otherwise you will get a compilation error. For example, you can use it for WGL and OpenGL 1.1 on Windows or GLX and OpenGL 1.3 on Linux, because Windows and Linux are guanteed to provide implementations for these APIs.

You will need to manually provide the linkage. For example to use WGL or OpenGL 1.1 on Windows, you will need to add #[link="OpenGL32.lib"] extern {} somewhere in your code.

Custom Generators

The gl_generator crate is extensible. This is a niche feature useful only in very rare cases. To create a custom generator, create a new plugin crate which depends on gl_generator. Then, implement the gl_generator::Generator trait and in your plugin registrar, register a function which calls gl_generator::generate_bindings with your custom generator and its name.

davorb / gl-rs