CGRectZero is the rectangle at point (0, 0) with zero size. For an
empty rectangle that will work correctly with CGRectUnion you need to
use CGRectNull instead.
John
On May 20, 2009, at 11:45 AM, Gordon Apple wrote:
IMHO, if it works the way you describe, it's doing the right thing,
at least
mathematically speaking from a point-set viewpoint. Unfortunately,
NSUnionRect works like the docs describe, which is not what I
needed, so I
wrote my own. It's too bad NSUnionRect and CGRectUnion appear to
not be
consistent. I believe the thinking (at least for NSUnionRect) is
that an
empty rect is no rect -- sort of an area zero.
The important thing is to know exactly WHAT they are doing and
either accept
it, or roll your own. This stuff is probably too deeply embedded in
everything to expect them to change it.
I just stumbled over this issue with CGRectUnion when one operand is
an empty rect, or has negative width or hight:
CGRect r1 = CGRectZero;
CGRect r2 = CGRectMake(100.0, 100.0, 300.0, 300.0);
CGRect r3 = CGRectUnion(r1, r2);
the result for r3 is actually :
r3.origin: (0, 0)
r3.size: (300, 300)
However, according the docs:
"if one of the rectangles has 0 (or negative) width or height, a copy
of the other rectangle is returned; "
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