Cannot export transparent images

[timonus]

I’m working on an app using Uber Signature that has a white stroke color against a black background. While editing everything works fine, but when I export the image the white stroke is composited onto an opaque white background. Would be nice to support exporting images with transparent background images.

I’m working on trying to add this, will contribute it back if I can get it working.

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[timonus]

Oops, just kidding! I was flattening these using UIImageJPEGRepresentation, which implicitly draws transparency on a white background.