CSC/ECE 517 Fall 2019 - M1951. Implement missing OffscreenCanvas APIs: Difference between revisions
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* [https://github.com/servo/servo/issues/24536 Add set_bitmap_dimensions method to CanvasState] | * [https://github.com/servo/servo/issues/24536 Add set_bitmap_dimensions method to CanvasState] | ||
In our instruction we were told to first pursue fix the [https://github.com/servo/servo/issues/24271 image data issue], then [https://github.com/servo/servo/issues/24269 add support for drawing offscreen canvases onto other canvases] | In our instruction we were told to first pursue fix the [https://github.com/servo/servo/issues/24271 image data issue], then [https://github.com/servo/servo/issues/24269 add support for drawing offscreen canvases onto other canvases]. | ||
=='''Current Progress'''== | =='''Current Progress'''== | ||
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=='''Code Changes'''== | =='''Code Changes'''== | ||
The first major step in better supporting offscreen canvases was to make sure that the parameterization types were ubiquitous across all canvas contexts. In most cases this required a simple change such as changing size integers to cast to 32 or 64 bit integers. This shows up in about a dozen files with the only difference being calls to cast functions or strongly typed parameterizations. An example is given below. | |||
[[File:diff1.png]] | |||
=='''References'''== | =='''References'''== | ||
Revision as of 02:36, 7 November 2019
Servo is an open source, Mozilla led project with the goal of creating a modern web engine with a highly parallel back-end. In this project, we are working on implementing several missing features related to drawing to offscreen HTML canvases.
Introduction
Servo
Servo is an open source layout engine for web content being developed by Mozilla and about 1000 contributors. It differs from previous engines by offering low level parallelism in rendering web components. Servo is designed to be cross platform with builds supporting Windows, Linux, Mac OS, and Android. Servo is written in Rust and tested using Javascript and HTML.
Rust
The bulk of Servo is written in Rust, an open source static compiled language that is largely similar to C++. Compared to similar languages, Rust adds fine grained control of coherency and memory layout, while offering safer threading and concurrency.
OffscreenCanvas API
The OffscreenCanvas API is a web API designed to render web content in a container not currently displayed on screen. These canvases can support a wide range of content. Our project deals with implementing and fixing some of the method implementations in Servo. As of writing, only Chrome 69+ and Opera 56+ fully support the OffscreenCanvas API.
Project Description
Getting servo set up and ready to run requires a few dependencies, namely in installation of the Rust Toolchain and Python 2.7. More specific setup instructions can be found in the Servo README.md. After dependencies are installed and the Servo repo cloned, the following script will build the dev version of Servo:
cd servo ./mach build --dev
At this point tests can be run using the following command:
./mach run <path_to_test_dir>
To achieve our project goals we were assigned several issues to look at. These issues cover the high level steps to improve the support of the OffscreenCanvas API. These issues are listed here:
- Getting pixel data returns blank pixels
- Support drawing offscreen canvases onto other canvases
- Support converting offscreen canvas data into a blob
- Implement linking offscreen canvases to placeholder canvases
In addition to these issues we have also been directed to a couple more issues that also deal with the OffscreenCanvas API:
- Make offscreen canvas rendering context use offscreen canvas' size
- Add set_bitmap_dimensions method to CanvasState
In our instruction we were told to first pursue fix the image data issue, then add support for drawing offscreen canvases onto other canvases.
Current Progress
In each of these github issues that we have worked on we have there are a thread of our communications with the project owners. The initial pixel issue seems to have been resolved by another user. The bulk of our time in resolving the paramount issue has been spent working on the two issues that serve as prerequisites for drawing one offscreen canvas onto another canvas. Our first pull request addressed these issues and allowed us to get feedback on our work towards our primary goals. Our second pull request rebases our first and takes into account some of our feedback, in addition to finishing the refactoring issue.
Code Changes
The first major step in better supporting offscreen canvases was to make sure that the parameterization types were ubiquitous across all canvas contexts. In most cases this required a simple change such as changing size integers to cast to 32 or 64 bit integers. This shows up in about a dozen files with the only difference being calls to cast functions or strongly typed parameterizations. An example is given below.
References
1. https://en.wikipedia.org/wiki/Servo_(layout_engine)
2. https://doc.rust-lang.org/book/title-page.html
3. https://developer.mozilla.org/en-US/docs/Web/API/OffscreenCanvas
4. https://rustup.rs/
5. https://github.com/servo/servo/blob/master/README.md
6. https://github.com/servo/servo/issues/24271
7. https://github.com/servo/servo/issues/24269
8. https://github.com/servo/servo/issues/24272
9. https://github.com/servo/servo/issues/24273
10. https://github.com/servo/servo/issues/24465
11. https://github.com/servo/servo/issues/24536
12. https://github.com/servo/servo/pull/24518
13. https://github.com/servo/servo/pull/24524