[css-paint-api] Converting a URL to a CanvasImageSource?

[asajeffrey]

PaintRenderingContext2D (https://drafts.css-houdini.org/css-paint-api/#2d-rendering-context) implements CanvasDrawImage (https://html.spec.whatwg.org/multipage/canvas.html#canvasdrawimage), which uses CanvasImageSource as the type of its image argument (https://html.spec.whatwg.org/multipage/canvas.html#canvasimagesource).

In examples such as https://github.com/w3c/web-platform-tests/blob/740aba06484bcb174c692175493fa591d29feedd/css-paint-api/paint2d-image.html#L20, the image is a URL. It is not obvious from the spec how this should be converted to a CanvasImageSource. In particular, paint worklets do not have access to the HTMLImageElement class, as it is not marked Exposed=(Window,PaintWorklet).

[asajeffrey]

Looking at what Chrome does, the properties map contains a CSSURLImageValue (https://drafts.css-houdini.org/css-typed-om-1/#cssimagevalue). Presumably CanvasImageSource is extended to allow CSSURLImageValue arguments?

[bfgeek]

Hey - yeah basically CSSImageValue becomes a valid CanvasImageSource, I had a PR on HTML to extend it in this way for a while, but will write the monkey patch here for the moment instead...

[asajeffrey]

@bfgeek thanks!