The Android P editing tool currently referred to as "Markup" is now unofficially available to download. This is a feature which was noted as included with the first developer preview of Android P after it became available yesterday. However, as Android P is only available to owners of a first or second-generation Google Pixel phone, the availability of the feature remains pretty limited at the moment.
This is where this app comes in as the feature has been extracted from the Android P preview build and made available to more devices. Likewise, as this is an Android P-free app, it is one which can be installed on any device running pretty much any Android OS version, though your mileage may vary on whether it works, and if it does, how well it works. Speaking of which, the developer who extracted Markup does note that a couple of minor changes had to be made. For example, in the original unmodified version users could simply click the 'Edit" button in the "Screenshot saved" notification to launch the feature. On this modified version users need to click on the "Share" button instead. From there, the option to launch Markup will become available.
For those new to this feature, Markup is basically a lightweight image editing tool which is now expected to come packaged with Android P when the consumer-ready version is released. It is primarily designed to allow users to annotate screenshots or crop them, though it does also seem to work with photos taken with the camera. While the app works well considering it is in a early state, one inconvenience is the lack of access to the edited image – as you cannot directly share an image immediately after annotating or cropping it. Although this is in line with the original version and therefore not an issue with this unofficial port itself, but more so one with Markup in general. To be able to share edited images users will need to launch a file manager app to access the image which will be located in a new folder – likely under "Pictures." Once found, the image can then be shared in the normal way.