First off, thank you for creating this amazing app; the brush engine and the robust canvas editing features combined have provided potentially the most comfortable drawing experience on the iPad for me, and is nothing short of amazing. However, as the title suggests, a quick horizontal flip feature, unlike the one already available in the menus involving direct and immediate alterations to the file itself, but much more in the fashion of say Clip Studio Paint or MediBang Paint for example where the user gets to toggle a reversed canvas view on the fly as a means of previewing rather than editing outright, is very much needed. As has been mentioned elsewhere on other forums, while flipping isn’t impossible per se as it is now, it does (1) break the workflow when you have to go through those extra taps, when in comparison in the aforementioned apps the flip is provided as a convenient optional shortcut, and (2) becomes more conspicuous an issue especially when dealing with larger canvases and/or with multiple layers simultaneously, since it consumes up to quite a few seconds to process the actual changes to the files.
The devil is always in the details, but this app is shaping up to become something quite spectacular, and it would be a shame to see it bogged down by small inconveniences like this. It must be no easy task to implement features, but I hope that you’ll take this (among others that are also quite rightfully needed) into consideration as you move forward with your updates. Best of wishes!