Only a little bit of math is neccessary to use affine transforms. A lot of
math is needed for general 3D programming, but let's ignore that for now.
My third grader was tought about associative and communitive math operstions.
Some matrix operations are associative and some are communitive. That's why
the order of operations matters.
To scale and rotate a square without moving the center of the square, do the
following:
A) translate to the center of the square making that position the new origin
for scaling and rotation.
B) Scale the coordinate system.
C) Rotate the coordinate system
D) Translate back to the original origin
F) Draw the square
It's not so hard typed in web-mail:
CGAffineTransform
TransformToScaleAndRotateAboutCenterOfSquare(NSRect someSquare)
{
CGAffineTransform transform = CGAffineTransformMakeTranslation(
NSMidX(someSquare), NSMidY(someSquare));
transform = CGAffineTransformScale (transform, 2.0f, 2.0f);
transform = CGAffineTransformRotate(transform, DEGS_TO_RADS(90));
transform = CGAffineTransformTranslate(transform, -NSMidX(someSquare),
-NSMidY(someSquare));
return transform;
}
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