https://static-misc.glitch.me/offscreen-rotate/

This demo gets pixel data for a rotated large bitmap.

On a 2017 Macbook pro, performing the operation locally takes 220ms. Performing the operation on an offscreen canvas takes 1400ms, as it causes a GPU switch.

To recreate the issue, you need to start with the integrated GPU active.

In our use-case (squoosh.app), we want to perform image processing in a worker, and kill the worker if it's idle. In our case, switching GPU is unnecessary (it just wastes the user's battery) and causes major jank during the switch.

I've attached a trace where I click each button, first performing the operation on a local canvas, then an offscreen canvas.
 

Deleted: trace_Mon_Nov_19_2018_13.56.54.json.gz 2.4 MB

trace_Mon_Nov_19_2018_13.56.54.json.gz 2.4 MB Download