Update: It really was as simple as not animating the UI element when utilizing touches. It perfectly follows touches now with no lag.
I'm currently attempting to implement a UI feature by implementing a CALayer subclass inside of a UIView subclass. I receive touch events in the custom UIVIew's corresponding view controller, notify the UIView about the touches, which in turn notifies the CALayer in order to animate the UI elements drawn in the layer.
It all works, but I have noticed that when there is a big delta in movement (as in when quickly scrolling a finger), the CABasicAnimation lags behind. Ideally I want the animation to stay perfectly aligned with the user's finger.
I've come up with a hacky way of just setting the animation's speed arbitrarily high as in
anim.speed = 10.0f;
which essentially keeps up with the user's finger, but I feel that this is a total hack and not a shippable solution. Should I be artificially limiting how many touch events are processed in order to solve this problem? Is there some sort of calculation I should be doing for the speed/duration of the animation that I'm not aware of?
Thanks for any help with this!
During the continuous gesture, one shouldn’t animate movements, but rather just move directly to the gesture’s location. When the gesture finishes, if you want it to settle in some other position, then animate that final, post-gesture, destination. But don’t animate during the gesture itself.
In rare cases, where rendering of a single frame is incredibly slow, there can still be perceived lagginess. Obviously, one should optimize the draw(_:) process so that it isn’t slow (or take a snapshot and animate the snapshot view rather than the complicated view). But during the gesture, you can also use “predictive touches,” where the OS estimates where user’s gesture is going to be in the future. For example, you can implement touchesMoved(_:with:) and then call predictedTouches(for:). By moving the view to the predicted touch location, it reduces perceived lagginess.
Related
I want to make a view/header collaspe/expand animation, but I also want to be able to pause or stop from expanding/collapsing while the user takes his finger off the screen.
I have a current implementation for this, but the animation is not very smooth.
I will also add some images to explain better what I want to do.
So the first image is how it should look when expanded.
The second image is how it should look if the user decides to take take his finger off the screen while he would scroll slowly so the animation/the view should stop in a state similar to that.
The third image is how it should look when it is collapsed.
If someone has any recommendation how I could achieve this I would be very grateful.
If you are targeting iOS 10+, use UIViewPropertyAnimator which encapsulates an animation and allows scrubbing and controlling the animation:
Start, pause, resume, and stop animations; see the methods of the UIViewAnimating protocol.
Add animation blocks after the original animations start using the addAnimations(_:) and addAnimations(_:delayFactor:) methods.
Scrub through a paused animation by modifying the fractionComplete property.
Change the animation’s direction using the isReversed property.
Modify the timing and duration of a partially complete animation by pausing the animation and using the continueAnimation(withTimingParameters:durationFactor:) method to finish it.
You just need to wire up touches to UIViewPropertyAnimator object encapsulating the animation.
There are many good tutorials on how to start with it, e.g. this one.
I'm using Ember-Gestures which implements Hammer.js in a Cordova app to implement some simple gesture controls.
I'm running into a major problem whereby any gesture that triggers an animation (transition, transform, SVG animations), if the screen is scrolling any amount, that animation will freeze and be at its end state when scrolling is complete. In particular, I have an element on a vertically scrollable page which should (ideally) be able to be pinched in and out to expand it into multiple elements or back into one.
I'm familiar that as an optimization iOS freezes all animation during scroll. However, since pinch and swipe gestures can both slightly scroll the screen, this is terrible for user experience because elaborate transitions can be completely frozen if the user swipes, for example, slightly up and to the left rather than just directly left.
I've tried a few solutions to enable rendering during scroll like those here, but these don't seem to work on contemporary versions of iOS. I've also tried the hammerJS e.preventDefault() method to freeze scrolling during gestures called through the Ember-gestures extension, so my method looks like:
swipeLeft(e) {
e.originalEvent.gesture.srcEvent.preventDefault()
// Do stuff
},
...but this doesn't have any appreciable effect. (Maybe there's something wrong here? gesture had no preventDefault() method itself, and ember-gestures seems to try to abstract some of this away.
Is there any way I can either keep animations rendering during scrolling (this seems unlikely), or alternately STOP a page from scrolling right before performing an animation (and prevent scroll while it's executing)?
Alternately is there any way I can add constraints to what is interpreted as a "pinch" or "swipe" gesture such that those that would also be interpreted as scroll gestures are excluded.
My solution here ended up being to add event handlers such that when the screen is touched with multiple fingers, the body is set to fixed position such that it's unscrollable for the duration of the touch (with the fixed position removed when touch is ended). I added the handlers to the pinchStart and pinchEnd events
I suspect there might be a more elegant solution out there, but for the purpose of disabling accidental scrolling while pinching so that D3.js animations won't freeze midway, this was a quick and effective fix.
Is there a way to observe the "time progress" of UIView.animateWithDuration...family of methods from UIView /alternatively CA animations?
I am animating a view's frame and I need to be informed how it is progressing.
My line of thinking was I can either
1) tap into CAAnimation related stuff or
2) observe the animated properties (like frame) and do my own calculations each screen frame.
Approach 1) turns out to be a dead end, inspecting the internal of how CAAnimations work told me absolutely nothing...and 2) is flawed as the "model layer tree is updated immediately and tapping into the presentation tree is difficult as the presentation layer is nil when you start.
I am pretty desperate, I was thinking that hooking into CADisplayLink will give me a tick and then I simply check something that is affected by the animation but there is nothing to tap to.
Do you think going the NSTimer way that is launched in the same scope as the animation method is ok? If I know animation duration then I can generate the progress myself.
If all you want is the time value, then you can do math on the CACurrentMediaTime() minus the animation start time. I have a sample project on Github called KeyframeViewAnimations that does exactly that.
That project supports pausing and resuming and scrubbing both UIView and CAAnimation based animations. In both cases it digs into the underlying CAAnimations.
I have another project that uses the values of the animated layer's presentationLayer in order to do hit testing so you can tap on an in-flight view and start/pause the animation. That one can be found here:
iOS-CAAnimation-group-demo
My code uses an NSTimer to update the progress of the animation. It would be better to use a CADisplayLink timer, as you mentioned.
I am also looking at the new UIViewPropertyAnimator class that was added to iOS 10. That makes pausing, reversing, and scrubbing UIView animations easy without having to dig into the underlying CAAnimations. See this thread I just posted:
Is there a way to observe changes to fractionComplete in UIViewPropertyAnimator
So I'm making a simple trivia game and I have a timerView that shrinks as time passes. When the user selects an answer, it needs to stop shrinking immediately - it must be very responsive. I give the user 10 seconds per question. Originally I would animate 10 times (with a duration of 1.0f), calling the next "segment" of animation in the completion block of the previous animation. In the completion block I would check to see if the user has tapped an answer, and if so I don't continue the chain. That solution works fine except that it's not very responsive because it's on a per second basis-- user taps an answer at the start of the second segment and the bar has a noticeable continuation.
My solution to THAT problem was to instead have 1000 animation calls with a duration of 0.01f. After doing that, the responsiveness was on point - the view stops animating as soon as I tap an answer -- the issue though, is that it's not actually 10 seconds, it takes more like 20.
So question number 1: what's the smallest time interval animateWithDuration can actually process properly?
Question number 2: is there a better way to accomplish what I'm trying to do accomplish?
ill answer question two: yes there definitely is a better way, have a look at CADisplayLink
use it to shrink your view a little bit each frame, and end the display link when you need to
the most responsive way is: the user taps an answer, you response in the touch callback, remove animations. you can remove animations by CALayer's removeAllAnimations method
Another way to do it is to set the view to shrinking using a single animation with linear timing, and then set the speed of the view's layer to 0 to pause the animation. When you set the speed on the layer to 0 the animation pauses instantly.
This works because under the covers, UIView animation actually creates and installs CAAnimation objects on the view's layers. It's possible to pause and continue an in-flight UIView animation just like you can a CAAnimation.
I have a project called KeyframeViewAnimations (link) on github that allows you to pause, continue, or "scrub" UIView and CAAnimations back and forth with a slider. You could use that technique. The tricky bit will be figuring out how far along the animation is.
What is the best way to implement a smooth reversing animation which tracks touches? I am referring to those animations in which, for example, if the user executes a swipe gesture some elements smoothly animate on screen, and others off, but if the user instead slowly drags a pan gesture back and forth the same objects will move forward/backward as a percent in accordance with the touch position. This is seen in many app intros and also in transitions. I have found
One tutorial which discusses the built-in facility for this but it is only between view controller transitions, not providing the full granular control I see in many apps (http://www.doubleencore.com/2013/09/ios-7-custom-transitions/)
Jazzhands, which is a kit by IFTTT, but this is a packaged solution that might not cover how the solution is best implemented at a lower level (https://github.com/IFTTT/JazzHands)
A question here for which one answer shows how you might execute an animation after a gesture ends (iOS Touch, Gestures, Animation)
What I don't grasp - and I'm comfortable using CAAnimations and gestures - is how something can be both animated and interactive.
Typically, when I create an animation, I commit the animation and it goes from start to finish. While I could interrupt the animation as touches continue, that seems like it would be stilted.
On the other hand, moving things in response to user input is easy, but that is not animated.
How is the effect achieved where something can change according to an animation, but also have that exact same animation occur tied to touches, and yet still also have it so that although the animation reaches completion it doesn't really "finish" (become irreversible) unless the user releases touch, while at any point during interaction if the user releases panning then the animation either reverts backwards to its starting position or animates to completion depending on the last touch location and velocity. These requirements are baffling.
The glimpses of this technique I see all involve keyframe animations, but what I don't understand is where the touch events intersect with an animation to create these smooth effects I see.
Any tips, examples, or tutorials are most welcome.
What I don't grasp - and I'm comfortable using CAAnimations and gestures - is how something can be both animated and interactive.
It is because, having set up an animation, you can set that animation to any "frame" you wish. Thus you can track the animation in correspondence to the movement of a gesture.
The way this works is that an animation is a feature of the render tree, belonging to a CALayer. CALayer implements the CAMediaTiming protocol. The timeOffset of a CALayer thus determines what "frame" of an animation that layer displays. If a complex animation involves many different layers, no problem; just set the timeOffset of their mutual superlayer, to control the frame of the entire animation.
That in fact is exactly how the new iOS 7 interactive custom transition feature works (to which you rightly refer in your question). For instance, in this example code:
https://github.com/mattneub/Programming-iOS-Book-Examples/blob/master/iOS7bookExamples/bk2ch06p296customAnimation2/ch19p620customAnimation1/AppDelegate.m
... I keep updating the UIPercentDrivenInteractiveTransition to tell it how far through the gesture the user is, and the animation therefore tracks the gesture. Now ask yourself: how the heck is this possible???
Well, the UIPercentDrivenInteractiveTransition, in turn, behind the scenes, keeps adjusting the layer's timeOffset to portray the animation at the corresponding frame. (You can actually add logging code to my example to see that this is true.)
Moreover, when I end the gesture at an incomplete point, the animation either hurries to its end or runs backwards to its beginning - again, this is because of the CAMediaTiming protocol, which lets you change the speed of the animation, including a negative value to run it backwards.