try this demo for your application
http://code4app.net/ios/Paint-Pad/4fcf74876803faec66000000
https://www.cocoacontrols.com/controls/smooth-line-view
https://www.cocoacontrols.com/controls/acedrawingview
https://www.cocoacontrols.com/controls/mgdrawingslate
it may help you.
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solved How to make a drawing program [closed]