Transforms - iOS Core Animation - page 78

3D Transforms
As the CG prefix indicates, the CGAffineTransform type belongs to the Core Graphics
framework. Core Graphics is a strictly 2D drawing API, and CGAffineTransform is
intended only for 2D transforms (that is, ones that apply only within a two-dimensional
plane).
In Chapter 3, we looked the zPosition property, which enables us to move layers
toward or away from the camera (the user's viewpoint). The transform property (which
is of type CATransform3D ) generalizes this idea, allowing us to both move and rotate a
layer in three dimensions.
Like CGAffineTransform , CATransform3D is a matrix. But instead of a 2-by-3
matrix, CATransform3D is a 4-by-4 matrix that is capable of arbitrarily transforming a
point in 3D (see Figure 5.6).
Figure 5.6 The CATransform3D matrix transforming a 3D point
Core Animation provides a number of functions that can be used to create and combine
CATransform3D matrices in exactly the same way as with CGAffineTransform
matrices. The functions are similar to the Core Graphics equivalents, but the 3D translation
and scaling functions provide an additional z argument, and the rotation function accepts an
x , y , and z argument in addition to the angle , which together form a vector that defines
the axis of rotation:
CATransform3DMakeRotation( CGFloat angle, CGFloat x, CGFloat y, CGFloat z)
CATransform3DMakeScale( CGFloat sx, CGFloat sy, CGFloat sz)
CATransform3DMakeTranslation( Gloat tx, CGFloat ty, CGFloat tz)
You should now be familiar with the X and Y axes, which extend to the right and down
respectively (although you may recall from Chapter 3 that this is only the case on iOS; on
Mac OS, the Y axis points upward). The Z axis is perpendicular to those axes and extends
outward toward the camera (see Figure 5.7).