Hi Duncan
Thanks for the answer - it does make sense (also in light of the other
replies to the same post). In my app, I've attached a simple 360
degree slider to the Y property, and I'd like that to rotate my layer
smoothly through the Y axis by 360 degrees. What I'm seeing then, is
that as soon as I get past 90 degrees, the solver returns these
'flipped' values for all three properties and the image jitters badly.
I must have stuffed something up though; because if the solver is
returning matrices that are 'equivalent' or mathematically equal -
then I should not see any visual difference in the rotation of the
layer on screen. But I do see visual differences.
The best way to see what i mean is a short vid; I first set the Y
rotation to 5 degrees, it looks OK, then I move the slider past 90,
and its this jitter that I want to eliminate. The video is at:
http://gallery.me.com/john_clayton#100148
The code is pretty simple, its a binding that goes through a
ValueTransformer - converting degrees to radians for a range of 0 >
degrees < 360, which then drives a simple setter on the CALayer
instance, that in turn modifies the "transform.rotation.x/y/z"
properties in turn.
Cheers - your help is [hugely] appreciated.
--
John Clayton
On 14/07/2008, at 8:35 PM, David Duncan wrote:
On Jul 14, 2008, at 9:57 AM, John Clayton wrote:
Huh?
Question 1: Why do X and Z get very close to PI?
Question 2: Why does Y end up being 1.02 when I set it to 2.12041?
Does anyone know what's going on here? I'm a little stumped by
this one.
The simple answer is that with a 4x4 rotation matrix, there are a
number of distinct matrices that are mathematically equivalent. Note
that 3.14 - 2.12 = 1.02 and that X & Z were flipped 180 degrees.
Effectively your seeing the solver for reversing an arbitrary 4x4
matrix into x/y/z rotations making certain simplifying assumptions
that don't match what you are expecting.
--
David Duncan
Apple DTS Animation and Printing
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