Re: CABasicAnimation, CALayers, and rotation
Re: CABasicAnimation, CALayers, and rotation
- Subject: Re: CABasicAnimation, CALayers, and rotation
- From: "Michael A. Crawford" <email@hidden>
- Date: Tue, 04 Nov 2008 18:13:43 -0800
Unless North is 0 and East is 90, which it is in my context after I
execute the following code snippet:
//
// Center and rotate the drawing context so that 0,0 is at the
center and
// zero degrees is at the top of the context.
//
CGContextTranslateCTM(ctx, CGRectGetMidX(layer.bounds),
CGRectGetMidY(layer.bounds));
CGContextScaleCTM(ctx, 1.0, -1.0);
CGContextRotateCTM(ctx, DegreesToRadians(-90.0));
I will consider your suggestion to convert the input so the I get the
desired rotational output from the layer. Thanks for that.
-Michael
On Nov 4, 2008, at 4:42 PM, Graham Cox wrote:
On 5 Nov 2008, at 11:30 am, Michael A. Crawford wrote:
By default, positive angle values assigned to a rotation animation
result in counter clockwise rotation. Is there a way to cause the
rotation to occur in the clock-wise direction, with positive
values? For example, consider a needle rotating in a compass. As
the needle rotates in a clockwise direction the value that the
needle points to increases (up until it wraps around, of course).
In mathematics, it is conventional that increasing angular values
imply counter-clockwise rotation, because a standard coordinate
system has its origin in the lower left corner, with the y axis
extending upwards from there.
Can't you just negate the angular value? Multiply it by -1 for
example.
There's no convention that I know of that says that "east" has a
greater value than "north" - you might find that not insisting on
that will make life easier.
hth, Graham
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