CSC/ECE 517 Fall 2016/M1652 ImageMap Support Servo

Image maps are an HTML technology that allows treating arbitrary areas in an image as separate hyperlinks. The goal of this project is to implement this missing feature on Servo.<ref>https://github.com/servo/servo/wiki/Image-maps-project</ref>

Introduction

Servo

Servo <ref> https://github.com/servo/servo </ref> is a web browser layout engine written in Rust<ref>https://github.com/rust-lang/rust</ref> and is currently being developed by Mozilla Research. The aim of the project is to create a highly parallel environment which allows several components to be handled by fine-grained, isolated tasks.<ref>https://en.wikipedia.org/wiki/Servo_(layout_engine)</ref>

Servo is built on top of Rust to provide a secure and reliable foundation and is focused on creating a reliable and fast browser engine.

Rust

Rust is a multi-paradigm, compiled programming language suited to create highly concurrent and highly safe systems. Rust is a modern, fast, memory-safe and multi-threaded programming language focusing on speed and safety to develop reliable and efficient systems. <ref> http://doc.rust-lang.org/nightly/book/README.html</ref>

Image Maps

In HTML and XHTML, an image map is a list of coordinates relating to a specific image, created in order to hyperlink areas of the image to different destinations (as opposed to a normal image link, in which the entire area of the image links to a single destination). Servo currently doesn't support image maps.

Approach and Implementation

Initial Steps

• Compile Servo and ensure that it runs on tests/html/about-mozilla.html
• An Area enum was defined in htmlareaelement.rs to handle rectangles, circles, and polygons (i.e. coordinate representations)
• Implement constructors for each variant that accept a string argument, parse them into appropriate coordinates, and return an appropriate Area instance
• Implement a hit_test method on Area that accepts a Point2D<f32> argument and returns true if the point is within the area's coordinates (return false for all polygonal areas)
• Write tests for the Area constructors and hit tests (add a new htmlareaelement.rs to tests/unit/script/ and run ./mach test-unit -p script)
• Add a method to HTMLAreaElement that returns an Area value derived from that element's attributes

Subsequent steps:

• Implement an areas method to HTMLImageElement that returns a vector of Root<HTMLAreaElement> values
• Implement a method to handle activation behavior on HTMLAreaElement
• Implement a handle_event method on HTMLImageElement to handle click events

UML Diagram

The following diagram depicts the classes involved to implement this feature:

Implementation Workflow

As can be seen in the image, the HTML code snippet defines a usemap attribute which handles a collection of shapes, dealt with by HTMLAreaelement. The corresponding shape's hit test method is called once the image has been clicked.

The workflow for implementing the support for image maps is as shown in the flowchart below:

Design Pattern

Design patterns are not applicable as our task involved implementing methods in a predefined object, namely HTMLAreaElement.

Testing

Test cases were implemented for testing the Area enum and the hit test functionality. Following are the steps to run all the tests:

1. Install the pre-requisites required for servo as mentioned here
2. Run the following commands to clone the repository and run the tests

git clone https://github.com/shravan-achar/servo.git

cd servo

git checkout master

To run the test cases

./mach test-unit -p script

The above command will download and compile the dependencies and the test cases. You will see that all tests pass as expected (Testcases are prefixed by HTMLAreaElement)

Testing From UI

The project is testable from the UI by handling clickable activities on this test link. The link has to be invoked from the compiled exe; the command for which is given below:

./mach build --debug

./mach run https://shravan-achar.github.io/imagemap

On clicking the image, the user is redirected to the next page ensuring that the functionality works appropriately on Servo.

References

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