Put a watermark over the canvas. Obviously on export/save don't 'flatten' the watermark layer on top, and don't remove the watermark layer until it's a paid app.
I have considered that possibility, but I despise watermarks and companies that use them. I want my users to be able to view and appreciate their creations, they just shouldn't be able to share it outside of my app without paying.
foidulus said:
Well it's definitely possible(certainly if you are willing to drop down into the "private APIs"), look at iTunes. You cannot capture part of the screen when a (iTunes store?) video is playing, all you get is a checkerboard...
I was hoping to have the app be a free download in the Mac App Store and then use IAP to unlock the full app - but I don't think Apple allows private APIs on the MAS.
I suppose I could just put a paid, unlocked, full version of the app on the MAS and then offer a free, uses private APIs to ensure you don't share, version of the app through my website... not sure if my web host would allow that or that Apple would be thrilled with me mentioning it in the app description on their store.
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:-/ Experimented with foidulus's method suggestion, but the system never seems to call that?
Blocking various other apps from taking screenshots is pretty easy... as soon as the app loses focus, block the window... heck, it even blocks screenshots from the terminal command, because that involves switching to the terminal application (although it doesn't block Grab > Timed Screen Shot, if the user then clicks back on the window,) but I can't for the life of me come up with how to block users from just using the keyboard shortcuts...
I tried using various TrackingRect methods but as soon as the user hits command-shift-4, it stops sending any updates until they either take a picture or hit escape.