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
• Delivered-to: email@hidden
• Delivered-to: email@hidden

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:

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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