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Re: NSBezierPath - quadratic curve with one control point?
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Re: NSBezierPath - quadratic curve with one control point?


  • Subject: Re: NSBezierPath - quadratic curve with one control point?
  • From: Daniel Jalkut <email@hidden>
  • Date: Sat, 17 Dec 2005 01:19:21 -0500

Hi Jim - I don't think Apple exports any mechanism to add a quadratic curve directly to an NSBezierPath.

As I understand it the math is easy to approximate quadratic curves as cubic, but not so the other way around. So I guess Apple decided to expose cubic curves in NSBezierPath and not bother with the convenience function required to convert from a quadratic.

You can search the web for various examples of converting the 3 points of a quadratic into the 4 points of a suitable cubic. Unfortunately, all the results make it look a lot more complicated than it is. But if you search this page:

http://support.microsoft.com/kb/q243285/

For the function "MakeBezierFromQBSpline," you'll find that each of the points is calculated with simple math and a reasonable comment explaining what's going on.

I think you'll be better off translating that logic into a convenience function of your own, than trying to find any way of coercing NSBezierPath to do what you want "off the shelf."

Daniel

On Dec 16, 2005, at 8:25 PM, Jim Correia wrote:

CGContext has two functions for dealing with quadratic curves - one take two control points and the other only one.

/* Append a quadratic curve from the current point to `(x, y)', with
* control point `(cpx, cpy)'. */
CG_EXTERN void CGContextAddQuadCurveToPoint(CGContextRef c, float cpx, float cpy, float x, float y);

How do I replicate that with NSBezierPath? (I want to keep the path around, not just render it and toss it.) The only method I see wants two control points.

Thanks,
Jim

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References: 
 >NSBezierPath - quadratic curve with one control point? (From: Jim Correia <email@hidden>)

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