Re: Drawing Invalidation Question
Re: Drawing Invalidation Question
- Subject: Re: Drawing Invalidation Question
- From: Michael Ash <email@hidden>
- Date: Sun, 1 Feb 2009 23:41:18 -0500
On Sun, Feb 1, 2009 at 4:05 PM, Seth Willits <email@hidden> wrote:
> On Feb 1, 2009, at 3:07 AM, Graham Cox wrote:
>
>> As others have mentioned, there is potentially a huge difference. If you
>> invalidate a lot of small rectangles, the update region might be quite
>> complex in shape; the <rect> passed in -drawRect: is only the bounds of this
>> complex area.
>
> Which is why the docs confused me. I knew there were subrectangles, but the
> weird thing was this line in the docs:
> "It is optimized to efficiently reject any rectangle that lies outside the
> bounding box of the area the receiver is being asked to draw in drawRect:."
>
> So it's not optimized to reject anything outside of the sub-rectangles? This
> sentence really threw me off. In retrospect and I can see that it simply
> means that it's doing a simple check up front like below, but it's a rather
> poorly worded description as it doesn't mention the sub-rectangles at all.
> Documentation fail. ;-)
You left out the word "efficiently" from the formulation of your
contrapositive, which I think is important. To me, the words
"optimized" and "efficiently" make it clear that it's only describing
a speed enhancement, and telling you that there's no need to do your
own bounding-rect culling beforehand. The full behavior of the method
is described at the top of the documentation.
Of course documentation quality and clarity is a matter of opinion,
and may vary.
Mike
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