CSC/ECE 517 Fall 2015/M1506-Refactor-GLES2-Implementation

' Refactor GLES2 Student Project with SERVO & RUST '

Servo is a prototype web browser engine written in the RUST language.Servo uses a variety of back-end implementations for drawing graphics depending on the operating system.One of such back-end is only compatible with Android right now, and we want to extend and refactor that back-end to enable on all Linux systems..

Introduction

Servo

ServoServo is an open source prototype web browser layout engine being developed by Mozilla, and it is written in Rust language. The main idea is to create a highly parallel environment, in which different components can be handled by fine grained, isolated tasks. The different components can be rendering, HTML parsing, etc.

Rust

Rust is an open source systems programming language developed by Mozilla. Servo is written in Rust. The main purpose behind it's design is to be thread safe and concurrent. The emphasis is also on speed, safety and control of memory layout.

Project Description

• The project requirement initially stated that we build and Compile servo. Following are the steps for this:

Servo is built with Cargo, the Rust package manager. Mozilla's Mach tools are used to orchestrate the build and other tasks.

   git clone https://github.com/servo/servo
   cd servo
   ./mach build --dev
   ./mach run tests/html/about-mozilla.html

• The next requirement was to build the Rust-layers independently of Servo. For this, we
• Next, we had to over-ride cargo to use our local copy of Rust-layers, so we had to add a cargo override to it. For this, we created a .cargo folder in our home directory(same place that servo and Rust-layers reside), and added a config file to that folder. The content of that config file is a path to our local Rust-layers.

   paths = [path/to/rust_layers]

• Next, we had to add a new command line argument in Servo, which would allow selecting the graphics background (GL or ES2). For this, we made the following changes:

- We added a command line option which lets the user enter the option -E or --es2 if the user wants to set ES2 as the graphic back end option. GL is set by default, hence if the user doesn't give any argument, Gl is selected as the graphic back end option. Example is as below

   ./mach run [url] -E

• Next, we had to add a flag in Rust-layers. This change was made in the file Rust/src/rendergl.rs in the RenderContext::new function. For this, we did the following change:

- We defined an enum GraphicOption which defined two options GL and ES2 and then based on the boolean value from the servo opts.rs, we set a variable with the respective enum value GL or ES2.

• Finally, we had to use the new command line option to pass the selected graphics back-end option to the Rust-layers context which we created in the previous step. For this we made changes to the compositor.rs in Compositing folder which is how Servo interacts with the Rust layers. The command line option is passed through the initialize_compositing function.

Requirement Analysis

Earlier, only OpenGL implementation was supported for Linux targets and we would be extending the ES2 implementation to support it for linux targets too. As a part of the final project, we propose to perform the following steps:

• Change the platform implementation to provide a more generic way to dynamically select between GL and ES2.
• Remove the Linux/Android specific #cfg flags.
• Place a general #cfg flag for both Android and Linux to provide a more generic implementation of dynamic selection between GL and ES2
• Make changes to EGL platform to make it work on desktop GL

Files modified

Servo/components/utils/opts.rs: added the new command line option to allow selecting the graphics backend. rust-layers/src/rendergl.rs: changed the RenderContext new function to allow the dynamic selection of graphics backend.

Files to be modified

rust-layers/src/platform/surface.rs: providing generic GL implementation that can dynamically select between the 2 interfaces.

Useful libraries

waffle-gl/waffle: A C library for selecting an OpenGL API and window system at runtime.

Design Pattern

The aim is to use ES2 implementation of rust layers for both android and Linux. So we need to use a design pattern that will allow us to extend the current implementation to support Linux targets too and give the user the flexibility to choose between the two implementations for rendering the backend.

We propose to use “Decorator” pattern. The decorator pattern gives the user the ability to choose between the implementations that are desired, and attach the corresponding implementation to the target dynamically at runtime.

To Be Determined Information

• Whether waffle-gl is to be imported, or simply used as example for base functionality
• Where android surface.rs implements ES2 vs GL (ie, what is the dividing line between a GL graphics implementation, and an ES2 graphics implementation).
• Acquiring Android interface to test modified “general” GL_ES implementation.

Conclusion

After making our changes , the user can now dynamically pass in the option of GL or ES2 through the graphic command line option, and this option is passed on through the compositor to the rust layers during initialization. A video demonstration for the code changes is available here

References

1. https://doc.rust-lang.org/stable/book/
2. https://en.wikipedia.org/wiki/Rust_(programming_language)
3. https://en.wikipedia.org/wiki/Servo_(layout_engine)
4. https://github.com/servo/servo/wiki/Refactor-GLES2-student-project
5. http://doc.crates.io/guide.html#overriding-dependencies
6. http://rustbyexample.com/
7. http://javarevisited.blogspot.com/2014/11/strategy-design-pattern-in-java-using-Enum-Example.html