A hacked up version of Apple's CIMicroPaint sample code adding a custom image accumulator, extra filter on the canvas, magnification, scrollbars, and a HUD.
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KNOWN ISSUES:
The CG HUD doesn't properly scroll with the canvas.
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TODO:
Move this to Metal some day.
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BUILD REQUIREMENTS:
Xcode 9 or later, MacOS v10.13 or later
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Portions Copyright (C) 2009-2012 Apple Inc. All rights reserved.