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Smooth Freehand Drawing on iOS

This tutorial will teach you how to implement an advanced drawing algorithm for smooth, freehand drawing on iOS devices. Read on!

Theoretical Overview

Touch is the primary way a user will interact with iOS devices. One of the most natural and obvious functionalities these devices are expected to provide is allowing the user to draw on the screen with their finger. There are many freehand drawing and note-taking apps currently in the App Store, and many companies even ask customers to sign an iDevice when making purchases. How do these applications actually work? Let's stop and think for a minute about what's going on "under the hood".

When a user scrolls a table view, pinches to enlarge a picture, or draws a curve in a painting app, the device display is rapidly updating (say, 60 times a second) and the application run-loop is constantly sampling the location of the user's finger(s). During this process the "analog" input of a finger dragging across the sc…