[Galene] Re: Blur background

[Juliusz Chroboczek <jch@irif.fr>]

> Yes, loading 3rdparty libraries is conceptually insecure. I initially
> tried to download the Javascript libraries and wasm modules to serve
> them via Galene, but failed because they refer to each other via full
> URL instead of relative paths when you load them.  I also tried to
> download their source code and build them myself, but my head exploded
> when I saw the kind of build system those libraries have.

Yeah, these are the two reasons I've been waiting for Chrome to implement
native background blur [1], but that effort appears to have been abandoned.

[1] https://chromestatus.com/feature/5077577782263808

>>> +    offscreen = new OffscreenCanvas(1920, 1080);

>> This should be done lazily, in the filter, not at startup.

> Not sure what you mean. How would you do this?

Two ways.  One is to add a function 'init' to your filter definition:

    'blur-background':
        description: "Blur Background",
        init: initBlurBackground,
        f: blurBackground,
    },

and then, in initBlurBackground, instantiate a new field in your filter:

    function initBlurBackground(ctx) {
        this.offscreen = new OffscreenCanvas(...)
        ...

The other solution is to simply do the initialisation in the main function
of the filter:

    if(!(offscreen in this)) {
        this.offscreen = new OffscreenCanvas(...)
        ...

In either case, the data structures are only created when the filter is
first invoked, which means that only users who use your filter pay the
cost of initialisation.

-- Juliusz