Re: Help with values for CATransform3DMakeRotation

FROM : Bill Dudney
DATE : Thu Feb 07 13:18:25 2008

Hi Devon,

It is typical for the vector that is rotated about to be a 'unit 
vector', not necessary but typical. The matrix you create here rotates 
about the vector from the origin to the point {20, 2.5, 1}, given the 
scale its more or less along the x axis that the rotation is 
happening. (normalize the vector with {x, y, z} / sqrt(x^2 + y^2 + 
z^2) => {20, 2.5, 1} / sqrt(400 + 6.25 + 1) => {0.991, 0.309, 0.050})

The red book on OpenGL is a great resource. You can find a version of 
it here;

http://www.opengl.org/documentation/red_book/

I'm not sure how much of the free online version pertains to OpenGL 
2.1 but the concepts of the 3D transformations have not changed since 
before there was an OpenGL.

Also, it would be most helpful to the rest of the people getting 
started if you were to file a bug against the docs WRT the 
transformation stuff;

http://bugreporter.apple.com

And provide some specific suggestions that would make the docs better 
for you and others getting started. Or hit the 'It was not helpful' 
link at the bottom of the doc and file the bug there.

Good luck and Hope this helps.

TTFN,

-bd-
http://bill.dudney.net/roller/objc

On Feb 7, 2008, at 12:44 AM, Mac Man wrote:

> I've been working on a perspective transform to get a rectangular 
> image to
> look like the Dock in Leopard (3D perspective look), and I've got the
> following code working to at least change the angle of the rectangle:
>
> NSView *contentView = [mainWindow contentView];
>
> CALayer *myLayer = [CALayer layer];
>
> myLayer.contents = [NSImage imageNamed:@"test.png"];
>
> myLayer.transform = CATransform3DMakeRotation(-.75,20,2.5,1);
>
> [contentView setLayer:myLayer];
>
> [contentView setWantsLayer:YES];
>
>
> The above code has the appropriate connections in Interface Builder, 
> of
> course.  The values I entered for CATransform3DMakeRotation are 
> arbitrary, I
> just don't understand enough of the math behind it to make any 
> sense.  I've
> googled perspective transformation matrices as suggested in a 
> different
> thread, but the values presented there didn't help at all.  Am I 
> missing
> something really simple with regards to CATransform3DMakeRotation? 
> The
> Apple documentation for the CATransform family in general is really 
> lacking,
> especially for people like me who don't have a background in graphics
> programing and heavier math!
>
>
> Any help anyone can provide in clearing things up for me would be 
> greatly
> appreciated!
>
>
> Devon
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