CODEWITHSUNDEEP
ioscore-graphicsuigesturerecognizersmoothingpan
samson
samson

Reputation: 1152

Smooth animation using drawRect: and UIPanGestureRecognizer

Ok. I HAVE seen a LOT of topics which are similar to what I'm trying to do here, but nothing that quite matches. Maybe my approach is way off base. Here's the deal.

I'm drawing a chart to my UIView subclass in drawRect:. I then use a UIPanGestureRecognizer to translate the chart's offset (internal, not in the view hierarchy) to the right/left. This works great, but my problem is that the recognizer's action gets fired with relatively low frequency. Specifically, the resultant panning is MUCH choppier than, say, in a scrollview or tableview. Particularly when the number of points in my chart goes up. Now, what I'd LIKE to do is not actually trigger drawing from the pan gesture's action, but have a timer firing at something like 30 times per second, interpolating the offset from the moment the pan fired to the current moment. However, this is getting more and more complicated.

Anybody have suggestions? Should I really just be doing this with a UIScrollView? The reason I'd prefer not to is that the data may extend quite far in either direction, and I'd like to not have to draw (or at least store) the whole path at once, but just do the section which is currently displayed. Should I be using CAShapeLayer? I'd like some input before I spend another day playing around with these possibilities...

Any input / experiences would by most welcome.

Upvotes: 1

Views: 791

Answers (1)

samson
samson

Reputation: 1152

So, in the end, I DID end up putting these things in a UIScrollView. I had to do quite a bit of work to get this up and running, the complicated part being the creation of a series of PANES which would be added to the scrollview. Each pane asks a delegate for the data it needs to draw, and then they're all stitched together. Fortunately, everything worked great once I put these scroll views containing chart panes into a table view. Still haven't tackled scaling, but I've seen a few posts on here which should make it relatively trivial.

So that's the answer to my original question. DON'T try to pan and draw on each frame, it WILL be choppy, and baring some real hack, there's no good way I could find to smooth it out. Scroll view handles all these problems for you, as long as you can split your view up nicely. I guess I could have used one long view, but then when the data set gets large I'm in trouble.

Now I've got a related problem though -- when offscreen charts scroll into view (they're in UITableViewCells), there's a big hiccup as the new chart gets drawn. I think I will try drawing them into an image asynchronously, so that when the new row scrolls into view, I've already got the image.

Upvotes: 1

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