shiny/driver/gldriver: flip y for mouse events

Cocoa uses the bottom-left as the origin.
Shiny uses the top-left as the origin.
Convert from one to the other when sending mouse events.

Fixes golang/go#12306

Change-Id: I462e813e260ec365c978624f9454e7ede0da833d
Reviewed-on: https://go-review.googlesource.com/13917
Reviewed-by: Rob Pike <r@golang.org>
1 file changed