Estimate Text Layout using an OffscreenCanvas

[jwagner]

I tried to use plotters in a web worker and ran into a panic in estimate_layout. The reason is fairly obvious, there is no window or document inside of a worker context.

To get plotters to work inside of a web worker I hacked up some code to measure the text size using an OffscreenCanvas.

There are some benefits and drawbacks to this.

I think it should be more resilient than creating a span in the dom and measuring offsetWidth/Height because it is not affected by CSS.

It should be more performant than adding a dom node and measuring the offset properties which cause layout reflows. This is just an educated guess. Didn't benchmark it - takes this claim with a pinch of salt.

I think the main drawback is compatibility. While it is considered to be baseline now, browser support isn't ideal.

There are several ways I see forward. This approach could be used as a fallback when window isn't available or visa versa.

I think it's also an option to just fall back to a really crude approximation along the lines of height = size, width = size * text.len().

Anyway would be glad to get some feedback on this from the maintainers.