Drawing Smooth Curves - Methods Needed

Question

How do you smooth a set of points in an iOS drawing app WHILE MOVING? I have tried UIBezierpaths but all I get are jagged ends where they intersect, when I just shift the po

Answer 1

For achieving this we need to use this method. BezierSpline the code is in C# to generate arrays of control points for a bezier spline. I converted this code to Objective C and it works brilliantly for me.

To convert the code from C# to Objective C. understand the C# code line by line, even if you dont know C#, u must be knowing C++/Java ?

While converting:

1. Replace Point struct used here with CGPoint.

2. Replace Point array with NSMutableArray and store NSvalues wrapping CGPoints in it.

3. Replace all double arrays with NSMutableArrays and store NSNumber wrapping double in it.

4. use objectAtIndex: method in case of subscript for accessing array elements.

5. use replaceObjectAtIndex:withObject: to store objects at specific index.

   Remember that NSMutableArray is a linkedList and what C# uses are dynamic arrays so they already have existing indices. In your case, in a NSMutableArray if it is empty, you cant store objects at random indices as the C# code does. they at times in this C# code, populate index 1 before index 0 and they can do so as index 1 exists. in NSMutabelArrays here, index 1 should be there if u want to call replaceObject on it. so before storing anything make a method that will add n NSNull objects in the NSMutableArray.

ALSO :

well this logic has a static method that will accept an array of points and give you two arrays:-

1. array of first control points.

2. array of second control points.

These arrays will hold first and second control point for each curve between two points you pass in the first array.

In my case, I already had all the points and I could draw curve through them.

In you case while drawing, you will need to some how supply a set of points through which you want a smooth curve to pass.

and refresh by calling setNeedsDisplay and draw the spline which is nothing but UIBezierPath between two adjacent points in the first array. and taking control points from both the control point arrays index wise.

Problem in your case is that, its difficult to understand while moving what all critical points to take.

What you can do is: Simply while moving the finger keep drawing straight lines between previous and current point. Lines will be so small that it wont be visible to naked eye that they are small small straight lines unless you zoom in.

UPDATE

Anyone interested in an Objective C implementation of the link above can refer to

this GitHub repo.

I wrote it sometime back and it doesn't support ARC, but you can easily edit it and remove few release and autorelease calls and get it working with ARC.

This one just generates two arrays of control points for a set of points which one wants to join using bezier spline.