CSC517 OffScreenCanvas Servo

About Off Screen Canvas:

The HTML specification defines a <canvas> element that can use a 2d or 3d rendering context. A new specification was recently developed that defines a canvas that can be used without being associated with an in-page canvas element, allowing for more efficient rendering. To use the OffscreenCanvas API, we have used a RenderingContext that has been obtained from an OffscreenCanvas object to generate new frames. Once a new frame has finished rendering in this context, the transferToImageBitmap() method can be called to save the most recent rendered image. This method returns an ImageBitmap object, which can be used in a variety of Web APIs and also in a second canvas without creating a transfer copy.

Problem Statement:

The following tasks were accomplished in the project:

• Creating the OffscreenCanvas and OffscreenCanvasRenderingContext2d interfaces with stub method implementations.

• Implementing the OffscreenCanvas Constructor [1] that creates a new canvas.

• The OffscreenCanvas Constructor has essentially 2 properties: OffscreenCanvas.width and OffscreenCanvas.height, which represents the width and height of the canvas respectively.

• The constructor also has the method OffscreenCanvas.getContext().

Web IDL

Web IDL is an interface definition language that can be used to describe interfaces that are intended to be implemented in web browsers. It is an IDL variant with:

• A number of features that allow one to more easily describe the behavior of common script objects in a web context.

• A mapping of how interfaces described with Web IDL correspond to language constructs within an ECMAScript execution environment.

Code Flow

• First, IDL files namely OffScreenCanvas.webidl and OffScreenCanvasRenderingContext2D.webidl were added at the locations components/script/dom/webidls/OffScreenCanvas.webidl and components/script/dom/webidls/OffScreenCanvasRenderingContext2D.webidl respectively.