Re: scrolling and drawing porblems
Re: scrolling and drawing porblems
- Subject: Re: scrolling and drawing porblems
- From: Ivan Kourtev <email@hidden>
- Date: Tue, 7 Nov 2006 16:26:47 -0500
On Nov 7, 2006, at 4:11 PM, m wrote:
Then you'll probably need to do something like let the scroll view
copy on scroll, then in your view's drawRect: method, draw "outside
the lines" of the rect you get as a peramter. Basically redraw
where your static stuff was before scrolling and where it should be
after.
Unfortunately, that doesn't work for two reasons:
1. I don't know what the scroll was, in fact I don't even know
whether drawRect was called because of a scrolling action. Maybe I
can setup some complex logic in my view do find out whether the
visible rectangle has changed but I am trying to avoid this if possible.
2. Drawing outside the drawRect's argument seems to have no effect -
I think maybe the drawing gets clipped?
On Nov 7, 2006, at 12:52 PM, Ivan Kourtev wrote:
On Nov 7, 2006, at 3:43 PM, m wrote:
On Nov 7, 2006, at 12:25 PM, Ivan Kourtev wrote:
I want to have a certain object drawn at a constant position
relative to the visible rectangle of my custom view (so that
it's always visible). The problem was that the my custom view
was in a scroll view that by default copies view content on
scroll. As both you and Eric suggested one way to accomplish
what I wanted was to disable the copying. Indeed, something
like [[self enclosingScrollView] setCopiesOnScroll:NO]; in my
custom view did the job.
The side effect of this is that since there is no copying
anymore, the argument to drawRect in my custom view after
scrolling is the entire visible rectangle (rather than just a
small strip exposed after scrolling).
Is this a problem in fact or in theory? Put another way, are you
noticing (as a user) a performance impact as a result of having
to redraw the while view instead of just a bit? Depending on how
complex and expensive your drawing is, you might find the code
complexity required (time spent coding, fixing, maintaining) to
optimize drawing doesn't pay off in substantial user perceived
responsiveness.
I absolutely agree but in this particular case performance is
impacted significantly indeed.
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