Re: Coordinate Rotation at a Point
Re: Coordinate Rotation at a Point
- Subject: Re: Coordinate Rotation at a Point
- From: Ron Fleckner <email@hidden>
- Date: Tue, 6 Nov 2007 16:47:04 +1100
On 06/11/2007, at 4:33 PM, Gordon Apple wrote:
Although I found references to rotating a Bezier path,
searching for
rotating coordinates at a point wasn't fruitful. In my case, I
wanted to
rotate a shape in place about its center, including shading and/or
content.
I believe the following is about as simple as you can get and can
be used to
rotate about any point.
@implementation NSAffineTransform (RTPTransformAdditions)
- (void)rotate:(float)angle atPoint:(NSPoint)point
{
[self rotateByDegrees:angle];
NSAffineTransform* pointXfrm = [NSAffineTransform transform];
[pointXfrm rotateByDegrees:-angle]; // Needed to get
original
point in rotated coordinates.
NSPoint oldPoint = [pointXfrm transformPoint:point];
float x = oldPoint.x - point.x;
float y = oldPoint.y - point.y;
[self translateXBy:x yBy:y]; // Done in the rotated
coordinates.
}
Hey, I think I know how to do this the easy way, thanks to Eric Buck:
To rotate about some point, translate to that point, rotate, and then
translate back. The approach is not Cocoa specific and is covered in
any introductory graphics text book.
so, [theTransform translateToPoint:(thePointYouWantToRotateAround)];
[theTransform rotateByWhatever];
[theTransform translateToPoint:(-thePointYouWantToRotateAround)];
[theTransform concat];
I forget the NSTransformer method names, but I think the intent is
clear.
Ron
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