Add support for alpha-testing in sprite picking backend #14929
Description
> Not sure what you mean by "test against alpha". Could you elaborate? EDIT - By that, do you mean whether or not the sprite is visible due to alpha/invisible texels? I'll add docs for that.
Exactly. I think most users would expect fully transparent pixels to not be hittable. Might be something where the backend/component specifies a threshold, so any alpha below that value will be ignored. Doesn't need to be added right now, but would be nice to mention in the plugin docs.
Originally posted by @aevyrie in #14757 (comment)
We can either add a whole new backend for this, or add a configuration option to the existing backend. Checking the alpha value of each pixel is more expensive but more intuitive and should be enabled by default with a way to toggle it off.