Simon Willison’s Weblog

24th May 2023 - Link Blog

Instant colour fill with HTML Canvas (via) Shane O'Sullivan describes how to implement instant colour fill using HTML Canvas and some really clever tricks with Web Workers. A new technique to me is passing a canvas.getImageData() object to a Web Worker via worker.postMessage({action: "process", buffer: imageData.data.buffer}, [imageData.data.buffer]) where that second argument is a list of objects to "transfer ownership of" - then the worker can create a new ImageData(), populate it and transfer ownership of that back to the parent window.