Advanced Touch Input on iOS

Session 233 WWDC 2015

Learn about the touch input and drawing pipelines. Gain specific insights in how best to design your app to minimize latency in receiving touches and maximizing the performance of drawing content on the screen. Explore new API in UIKit and learn best practices for faster and smoother input.

[ Applause ]

PETER TSOI: Hey, everyone.

Good afternoon.

And welcome to Advanced Touch Input on iOS.

My name is Peter.

I work on the iOS Performance team on Apple.

Today with my friend Jacob, from the UIKit team, we would like to tell you a little bit more about how touch input works on iOS and how you can use that information to make your applications even more responsive to touch input.

We've got a lot to talk about today.

As the previous slide alluded to, reducing latency is the name of the game when it comes to making your applications even more responsive.

We will talk about what latency is and why you should care about latency in your application and latency in iOS as a whole.

In order to discuss where this latency comes from, we will discuss and dissect the major pieces of iOS, which are responsible for everything between handling your touch input to drawing the pixels underneath your finger in response to that touch.

We have made a lot of improvements to this system over the last year in iOS 9, and we would like to tell you about the improvements as well as some of the APIs you guys can use to take advantage of all these improvements we have made.

And finally, we would like to leave you with some tips and best practices about how to find, diagnose, and fix the performance bottlenecks in your application.

So why should you care about reducing latency in your application?

Touch input on iOS is built around the idea of direct manipulation.

This is the idea that a user is actually touching a physical object with their finger and moving it around in a virtual space.

For example, if a user was trying to move this circle from point A to point B, the expected result is that the circle feels glued to the end of the finger.

You'll notice that in this example, the circle tracks very precisely and responsively with the user's finger.

However, as soon as you reduce latency, or the lag between when the finger moves and the circle moves, this illusion of direct manipulation starts to break down.

In this case, you can see that the circle is following the finger and it doesn't feel like you are moving it around with your finger anymore.

This effect is compounded when the user is moving really quickly.

In this case, the finger gets a substantial distance away from the circle, and it no longer feels like the finger is glued to the circle, rather the circle is now playing catch-up with the finger.

So this type of latency affects iOS as a whole, from everything from button presses to moving objects around, to scrolling anything even a web page.

But we have identified a couple of applications where increases in latency are even more noticeable.

One of these types of applications are drawing applications.

Not only is the artist then distracted by the amount of distance between the end of the line and a user's finger.

Artists often rely on quick, responsive updates to their application or to the user interface in order to quickly adjust their physical behaviors in order to get the result they are going for.

In addition, latency in applications like games makes the games harder to play, in effect the perceived quality of your application.

Where does this latency come from?

It comes from a lot of different places.

In order to discuss where it's caused, we'll discuss all of the different parts of the system involved in handling your touches and drawing the touches in response.

Throughout the next portion of the talk, we will be relying heavily on these pipeline diagrams.

So let's make sure we are all on the same page as to what they mean.

Up on the screen, you see five different boxes.

Each of these boxes represents the amount of time a frame is shown on the display for.

Our products refresh the screen at 60 hertz or 60 times per second.

So the amount of time represented by each of these boxes is approximately one-sixtieth of a second.

You may hear me refer to each of these boxes as a display frame, a display interval, or a display cycle.

They all mean the same thing.

Now, the vertical lines separating each of these boxes is the display refresh.

This is the point in time where one frame on the display is swapped out with the next one to be shown.

You will hear me refer to this as either the display refresh or the v-sync, again they mean basically the same thing.

The display refresh is important in iOS because many important system processes are kicked off or triggered by this display refresh.

So let's actually talk about what's going on inside this pipeline.

The first stage of the pipeline is Multi-Touch.

This is the process where the hardware will scan the surface of the display looking for touches.

On most of our products, this can take less than the entire display frame, but on some of our products, it can take up to that entire display frame.

In order to symbolize that, we will fill in the entire box with this green box.

Once Multi-Touch is finished scanning this display and is finished filtering out any of the noise which was present on this screen, your UI application's UITouch callback will be called near the beginning of the next touch frame, usually right after a display refresh has occurred.

This is the point in time where your application should respond to the touch inputs and, in a drawing application, maybe plot the points and connect the dots in between.

You may want to do any smoothing to make the line very smooth.

In an application that isn't a drawing application, this is where you would respond to button presses or key presses, maybe create views, view controllers and present them to the user.

The amount of time spent here is variable, but can take up to one display frame.

So, again, I filled in the entire box.

Once your application is done responding to the touch events and has updated the state accordingly, Core Animation will wake up at the next display refresh and begin translating your views and your layers into GPU commands that can be rendered by the GPU.

You will notice that the GPU does not have to wait until the next display refresh to begin.

It begins immediately as soon as Core Animation has given it the instructions that it needs to render the frame.

Again, the time in these stages is variable, based upon how complicated the views in your application are.

Finally, once the GPU has finished rendering your frame, that frame is then enqueued to be displayed on the display once the next display refresh occurs.

As you can tell, between sensing your touch on the display, all the way through to drawing it, can take several frames.

In this case, it takes four frames.

So it's not instant.

In addition, this is a pipeline.

So other touches that may occur while your application is processing that previous touch can also be happening.

These just go through the process at different points in the pipeline.

Let's talk about what you as a developer have control over.

There are no APIs to alter the behavior of the Multi-Touch or the display hardware layers.

This is handled for you by the system.

You exercise indirect control over the Core Animation render server and the GPU based on how complicated the views in your application are.

But you have almost complete control over your application.

So that's where we will begin.

As I mentioned earlier, this is the point where you update the stay of your application in response to the touch inputs.

For example, in a drawing application, you plot the points and connect them, or you create views in response to button presses.

This also might be where you issue your OpenGL or Metal commands.

The amount of time spent here is variable.

You can optimize this to take a smaller amount of time, and we encourage you to do this, but you will notice that when we optimize the application, Core Animation does not slide in to fill in the space left behind by UIKit or your application.

This is because of how updates to your views have worked historically in the past on iOS.

When you update the state of your views on iOS, you can either explicitly commit A CATransaction or UIKit will implicitly generate one for you if you update the views properties with the UIMethods.

We will represent this CATransaction commit with this red dot.

Now, the reason why Core Animation doesn't slide in to fill in the time is because your application is allowed to update its state several time during one display frame, in this case, symbolized by the second dot.

Now, in order to reduce the amount of redundant work or work that will never be shown on the display, Core Animation will batch up all of your updates and render it once at the display refresh.

So we will only render the combined state of both of those Core Animation transactions.

Once Core Animation decides to snapshot your view at the display refresh, it will begin translating all of the logical views and layers that you have created for it into GPU commands that can be rendered by the GPU.

As I mentioned earlier, the GPU starts immediately as soon as it has the necessary instructions from Core Animation.

So if you optimize the amount of time spent in Core Animation or in the GPU, the GPU will fill in the space that was left behind it.

The view debugger in Xcode is a very helpful way to understand how complicated your view hierarchy is and a great way to find views that you can take out and therefore optimize your application.

However, we recognize the need for views that are very complicated, that can't possibly be represented in one display frame.

So the iOS pipeline is flexible enough to handle that.

If your application needs to spend additional time rendering views, we can split the Core Animation and GPU work over two display frames.

Of course, this adds an additional frame of latency, but you can still get 60 frames per second smooth animations everywhere in your application, with more complicated views.

There is no manual trigger to go between the faster mode and the slower mode.

This, again, happens for you and is arbitrated by the system.

So it's important that we understand what things can trigger you into the faster mode and what things can trigger you into the slower mode.

The faster mode is called double buffering, and we call it this because there are two buffers, one for the GPU to draw into, and one for the LCD to show to the user.

At the display refresh, as you will recall, Core Animation grabs a buffer for it and the GPU to use, and it will begin outputting GPU commands for that frame.

Once the GPU has those commands, the GPU will begin rendering, and if the render completes before the next display refresh has to occur, we enqueue that frame for display at the next display refresh.

Once we reach that display refresh, the frame is then swapped onto the screen and we begin the process with the next frame.

Again, the GPU will render and then enqueue the frame for display at the next display refresh.

Once we hit that display refresh, these two frames will swap places, we will reclaim the green buffer and continue this process, as long as your application has views that it wants to render.

Now, this is all fine and good.

We have finished our Core Animation and our GPU work within one display frame.

We have good performance.

But what happens if you can't do all of this?

If you can't do it in one frame?

Then we fall into a mode called triple buffering.

Again, Core Animation will output GPU commands, which the GPU will then render but in this example, the GPU hasn't finished rendering the green frame by the time we hit the display refresh.

In this example, since we can't show it yet, the blue frame has to be extended on the screen for an extra frame.

Core Animation now needs to allocate a third buffer to begin work on the next frame, and it will do so by creating this third buffer.

Then Core Animation will start outputting GPU commands for it while the GPU finishes rendering the previous frame.

And then the previous frame will be enqueued for display at the next display refresh.

This process then repeats with the Core Animation render server outputting GPU commands, and the GPU will then render them.

You get the idea.

We swap the buffers, reclaim the buffer, and then the process repeats.

So you might be thinking, all of these slides say Core Animation.

What if I don't use Core Animation?

What if I have optimized my application to use Metal or OpenGL?

You might think instead of your pipeline looking like this and getting your frame out to the display in four frames of latency, that you can do it in three frames of latency.

Unfortunately that's not the case.

Under iOS 8, if you use Metal or OpenGL, Core Animation still acts an arbiter, to make sure that any updates you make to any Core Animation content on the screen are synchronized with any GPU, OpenGL, Metal updates that you make to those layers.

So you still have four frames of latency when you use OpenGL or Metal in iOS 8.

So we talked about how the iOS pipeline is flexible enough to handle very complicated views, getting you 60 frames per second animation but at five frames of latency and how you can optimize your application to bring that latency down to four frames by optimizing what you are drawing.

However, in this example, there is no real way to make it any faster, because Core Animation needs to wait until the display refresh to start generating the GPU commands.

In iOS 9, we are removing that dependency.

You can now start Core Animation work immediately as soon as your application is done updating the state of your application.

In order to take advantage of these, we have introduced some new APIs and new tricks in the iOS system.

To tell you a little bit more about them, I would like to introduce Jacob [applause].

JACOB XIAO: Thanks, Peter.

So I would like to tell you about some additions we have made in iOS 9, and how you can use them to get even lower latency in your apps.

I will be talking about three things today.

First, low latency support in Core Animation.

Then, a new system for touch coalescing, and finally, a really cool system for touch prediction that we built into UIKit.

So let's get started with low latency in Core Animation.

As Peter just showed you in iOS 8, even with a well-optimized app there was a limit to how far you could get your latency down.

By using low latency Core Animation in iOS 9, we can combine the app's frame with Core Animation frame, and this gives you much lower latency.

The best thing about this feature is that it happens automatically.

There are no changes you have to make to your app other than optimizing your performance.

However, there's one thing to keep in mind, which is that this low latency mode is automatically disabled when you have animations active in your app.

This includes CA animations and UIKit animations, so if you want the absolute lowest latency in your app, you want to make sure to disable those animations while touches are active on the display.

Now this system also works with Metal and OpenGL content.

So as you saw earlier before in iOS 8, we had to wait an additional frame to get your GPU content to the display.

But with the new low latency mode, we can now get that content to the display as quickly as possible in the very next frame.

This happens automatically just by using CAeagllayer or CAMetalLayer.

However, if there's one thing to keep in mind in your app if you have Core Animation content that you want to draw along with this OpenGL or Metal content.

In this case, the GPU content will be drawn to the display as quickly as possible but your Core Animation content may take a little longer to go through.

And if that happens, then by default, it's not guaranteed that your GPU content will arrive in the same frame as your Core Animation content.

Now this may be a problem if you want those two to be in sync, and that could happen, for example, if you had an OpenGL map view, that you wanted to draw UIKit content on top of.

In that case, you may want to synchronize those updates in something like this, and there's a property that allows you to do that called Presents With Transaction.

It's on CAeagllayer and CAMetalLayer.

When this is set to False, which is the default value, then it will get your GPU content to the display as quickly as possible.

But when you set it to True, then we synchronize your GPU content with the Core Animation content so they both appear on the display at the same time.

All right.

Next, let's talk about touch coalescing.

But before we do, I would like to tell you a little bit about the iPad Air 2.

We introduced the iPad Air 2 last year, and it has a 60-hertz display update rate, which means the display updates at 60 times per second like our other iOS devices.

It also has a really cool feature that affects touch and touch latency that I'm really excited to announce to you today.

And that's the fact that it has a 120-hertz touch scan update rate [applause].

It's pretty cool.

This means that it scans for touches at twice the rate of all other iOS devices.

And this is great, because you can get a lot more information about where the user's finger is going as they interact with the display.

Let's take a look at how this affects your app in practice.

With the 60-hertz touch scan rate, as the user's finger moves across the display, we will periodically sample where that finger is and give that information to the app.

The same thing happens with the 120-hertz scan rate, but since it's twice as fast, you get twice as many samples, and this gives you a lot more information about what the user is doing.

Now, once we get those samples, we will pass them to your app, and you can use those to know what the user is trying to do with their touches.

For example, in a drawing app, you might connect them together to represent the drawing that the user is trying to perform, and this 120-hertz information gives you a lot more information that you can use to get a better representation of their drawing.

So now that we have seen the benefits of 120-hertz touch scan rate, let's take a look at how it affects the touch to display pipeline.

This is the 60-hertz touch scan rate pipeline that we saw earlier.

And let's focus in on just the Multi-Touch stage of the pipeline.

At 60 hertz, we get a new touch sample every frame.

And with 120 hertz, we'll now get two samples every time.

However, note that the size of the display frame is still the same, since we have the same update rate for the display itself.

Now, we could take those new touch samples and pass them to your app, and your app could use that to update its drawing, which would update what it showed in Core Animation and on to the display.

But you will notice that if we did, that your app would actually be updating twice as often as the display updates, which would lead to wasted work in your app.

So we introduced the touch coalescing system to get the best of both worlds.

This allows you to get the increased information from the 120-hertz touch scan rate but not to have any wasted work in your app withdrawing too much.

Let's take a look at how this pipeline changes with coalescing.

Now we will only deliver a touch to your app once per display frame, so when the first touch comes in, we will deliver that to you.

And then in the next frame, we will deliver you the touch for that frame, and also any intermediate touches that happened since the last time we sent touches to your app.

This repeats each time the user makes more touches to the display.

We'll give you the current touch and any coalesce touches, and that continues as long as touches are active.

Now, the API to use these coalesced touches is really simple.

It's a new method on UIEvent called Coalesce Touches For Touch.

You pass into that method the touch that you're looking at, and we'll give you back an array of all the coalesced touches since the last time we delivered that touch to your app.

To get a better idea of how to use this API, let's look at how touch handling works in iOS in general.

When the user first touches the display, we will call Touches Began on your app.

As their finger moves, we will call Touches Moved, and finally, as their finger is removed from the display, we will call Touches Ended.

Now, as we are talking about these touch callbacks, another very important callback is Touches Canceled.

This gets called when the stream of touches to your app is interrupted.

For example, if the user swipes from the bottom to activate Control Center.

In that case, your app will get some the initial touch callback, and we will get Touches Canceled when the system gesture takes over.

It's important to implement this method to do any cleanup for things that you started in the previous touch callbacks and roll back any changes you made.

For example, in a drawing app, you might want to remove the line that the user was drawing.

So now that we have seen how these touch callbacks work, let's see how they interact with coalesce touches.

The touches we deliver to all of those callbacks are what we call main touches, and these work the same with the 120-hertz scan rate as they do with 60-hertz devices.

However, with the Coalesce Touches For Touch method, you can get access to more information with these coalesced touches.

The coalesced touches not only have information about the intermediate touches but they also give you a copy of the main touch itself.

And the great thing about this is that it allows you a choice.

You can look at the main touches if you don't need the increased information of the higher touch scan rate in your app, or, if you want that information, you can look at just the coalesced touches and you don't have to worry about the main touches.

So now let's revisit the touch sequence that we saw and see how that works with both main touches and coalesced touches.

As the user's finger comes down, we will give your app a main touch, and also a copy of that as a coalesced touch.

Then as their finger moves, we will deliver you new main touches and a set of coalesced touches for each one.

And finally, as their finger leaves, we will give you the last main touch and any remaining coalesced touches.

Now here, I have shown only one or two coalesced touches for each main touch.

But it's important to keep in mind that your app can receive a different amount.

If your app takes a long time to process a touch, then we will give you some time to catch up and wait to send you new touches until you have caught up.

And if this happens, then the touches that weren't delivered you to will be sent to you later as coalesced touches.

So make sure that you don't hard code any dependencies on the number of coalesced touches that you receive.

Now, there are a few differences between the way that coalesced touches behave and the way that main touches behave.

One of those is related to previous location.

And previous location is something that you can get with the method Previous Location In View from UITouch.

For main touches, this gives your app the last location that that touch had when it was delivered to you.

And for coalesced touches, it behaves very similarly.

It gives you the location of the last coalesced touch to your app.

And this is one of the reasons that it's really important to focus on just the main touches or just the coalesced touches.

That way, you won't get any confusion with the previous locations.

So it's really important not to cross the streams.

[ Applause ]

Now, another difference between main touches and coalesced touches is in how the UITouch objects themselves behave.

With main touches, the same UITouch instance is reused every time the touch is delivered to your app.

This is helpful because it allows you to differentiate between different touches if the users has multiple fingers on the display at once.

And for coalesced touches, this works a little bit differently.

There, each time we deliver a coalesced touch to your app, we deliver a new UITouch instance that has the new properties.

And so you can think of these as snapshots instead of the shared identity that the main touches have.

So now that you understand how touch coalescing works, let's dig into some code for how to use coalesced touches.

This is some code that you might have in an app that does something like drawing and you could have something like this in touches moved.

Here we are iterating through the touches that we have, and we are grabbing the line that corresponds to each touch.

Then we are adding the latest touch as a new sample onto the end of that line.

And to add touch coalescing support, we just need to add this small bit of code.

Now, we are iterating through all the coalesced touches for the given main touch, and for each of those coalesced touches, we are adding it for the sample to the line.

Notice that we are only adding the coalesced touches of the samples, not the main touches.

And that's touch coalescing.

Now I would like to tell you about touch prediction.

This is a really cool system that we have added right into UIKit that you can use to get even lower latency in your apps.

Now, as we deliver your app, new touches will also give you a look into the future at what we predict that the user's touches will be doing in the near future.

And the API for this works very similarly to the API for coalesced touches.

It's another method on UIEvent called Predicted Touches For Touch.

Once again, you pass in a main touch to this method and you will get back an array of predicted touches.

And you can use those predicted touches to update your drawing or whatever else you are doing with the user's touches, to get even lower latency.

So earlier, we saw how main touches and coalesced touches are related, and predicted touches work in a very similar way.

They are another set of touches associated with a main touch, and they behave as snapshots just like coalesced touches do.

Now, one thing that's different about predicted touches compared to coalesced touches is what happens when new touches come in.

As you get a new main touch, you will get a new set of predicted touches, and the new predicted touches are the only thing you want to use then.

Any previous predicted touches are no longer useful since we now have information about where the user actually touched during that time.

So you generally want to throw those old predicted touches out.

Now, previous location in view works similarly for predicted touches as it does for other touch types.

It points to the location that the previous predicted touch had, or, for the first predicted touch, it points to the last location that was delivered to your app.

So you may be wondering how we actually get these predicted touches, and it's pretty simple.

We built a time machine into every iOS device [laughter].

That's not quite how it works.

What we are actually doing is looking at the touches that are delivered to your app and using a set of highly tuned algorithms to determine where the user's finger looks like it's going at this time.

And as we get new touch samples, we will update our prediction and deliver new predicted touches to your app.

Now, each of those predicted touches are complete UITouch objects and they have all of their properties filled out, like their location and time stamp.

So now we can look at how those predicted touches affect the pipeline that we have been looking at.

This is what we saw earlier from main touches and coalesced touches, and we can easily add in predicted touches as well.

Each frame, as your app gets a main touch, you also get a set of predicted touches.

And if you get main touches and coalesced touches as well, then the predicted touches are just more information that you have available to you.

And this process just repeats as new touches are delivered.

One thing to note is that coalesced touches and predicted touches are independent.

You can use one without the other, and predicted touches are supported on both 60-hertz and 120-hertz touch scan rate devices.

So now let's take a look at how we can add touch prediction to the code that we were taking a look at earlier.

All you need to do is add this small bit of code, and what we are doing is first removing any previous predicted touches that we added to our line.

And this is important since we now have the actual locations where those touches were.

Then we are iterating through the predicted touches we have.

And for each of those predicted touches, we are adding it as a sample to our line.

But notice that we are calling a different method here to add the predicted sample as what we called to call the normal samples.

This is so that we can mark that sample as something that will need to be removed the next time we go through this code.

So that's touch coalescing and touch prediction.

Now that you have seen all of these techniques, let's see what happens when we combine them all together.

In iOS 8, with a well-optimized app, this was the touch latency view that you could get.

We measured the latency as the time between when the touch first comes down to when the display has updated with that touch's information.

And so you can see that in iOS 8, we would have four frames of latency.

Now by using low latency Core Animation and iOS 9, we can remove one frame of latency from that.

And by using touch coalescing and running on a high-touch-scan-rate device, you can not only get increased information about the user's touch, you can also remove a half frame of latency from the beginning [applause].

But there's more!

By also using touch prediction you can get information about approximately a frame into the future of where the user's touches are going.

And this lets you give the user an effective latency that's reduced by about a frame more as well.

And so altogether, in iOS 9, you can get down to approximately one and a half frames of latency for your users which is a huge improvement from iOS 8's four frames of latency.

[ Applause ]

So we think this is really great, and I highly encourage you to adopt these techniques in your app to give your users a great low latency experience.

Now I would like to turn things back over to Peter to tell you how to fine-tune your app.

[ Applause ]

PETER TSOI: Thanks, Jacob.

So now that you know about all of the new low latency modes in iOS 9, we would like to tell you how you can take advantage of those by fine-tuning your applications so you can fit within one display frame of time so you can get your frames out to the display that quickly.

The first way to ensure that your application is doing the least amount of work is to minimize the amount of work that your application needs to do.

By using the coalesced touches API that Jacob just introduced to you, you can get the benefits of high-fidelity touch inputs of the iPad Air 2 while making sure that your application only renders images that will make it onto the screen.

In addition, keep in mind that your user only cares about the content that they can see on the device's display.

Your application may do the work to keep track of the state of the world outside of the screen, but ultimately, you should make sure that the rendering work is restricted to only the work that is necessary to generate the image that ultimately shows up on the screen.

If you are trying to profile your application, to figure out how much time your application is spending on the CPU, Time Profiler is a great way to do this.

Time Profiler will show you how much time your application is using on the CPU by sampling it at a fixed interval.

In this case, in Time Profiler, I selected a 16-millisecond interval, which corresponds roughly to one display frame.

You can also tell that my application in this case is using only a small fraction of that amount of time.

In this case, 3 milliseconds.

Now this is all fine and good if you are trying to measure and profile how you are doing in terms of CPU work.

What about GPU work?

The frames per second gauge in the GPU report available in the Xcode debugging session give you a high-level view of your application's GPU performance.

In this case, you can see that this application is hitting 60 frames per second, and it has a relatively low amount of GPU frame time.

In this case, just 3.8 milliseconds.

Keep in mind, though, that this is just a high-level overview of what your application is doing.

It doesn't give you fine-grained information about individual frames that may be causing you to drop frames.

If you require that type of precision, then you will want to turn to the new GPU driver instrument, which we have introduced in Xcode this year.

The GPU driver instrument can show you exactly how long the GPU is active for while you are using your application.

In this case, you can see that the amount of time spent in the vertex and fragment shaders of my application is relatively small.

In fact, it's just a small fraction of the amount of time that a frame is shown on the display for.

Notice you only see two colors here.

These two colors represent the two buffers which are used in the double-buffering scheme.

If our application is spending more time in Core Animation and in GPU, you will see three colors here to represent the triple buffering which is happening in the system.

We have talked a lot about reducing latency and how to make your application more responsive, but ultimately, building a great iOS experience is about building a natural and intuitive experience for your user and making your application feel more alive is another great way of doing that.

Over the last year, we thought long and hard about each part of our system, and we found ways to make it better and faster than ever.

Throughout this process, we have improved our APIs to give you more control and more information over how the system works.

With the new low latency modes on OpenGL, Metal, and Core Animation, you have more control over when your frame is shown to the user and how it synchronizes with any other content you have on the screen.

With touch coalescing, you can take advantage of all of our hardware and all of its awesome capabilities to provide that to your user.

And with touch prediction, we are offering you a small glimpse into the future as to where that touch is going to go.

And finally, we have built and created some great tools in order for you to understand the performance of your application so that you can improve upon it to provide an even better experience for your users.

We at Apple are committed to making the experience of using our products feel more alive than ever, and we think reducing latency is a great way of doing that, and we would like to invite you along on this journey.

You can find more information about the technology, tools, and APIs we've discussed today at developer.apple.com.

We would also like to invite you to take part in the developer technical conversation on our developer forums.

We talked about a lot of different new technologies today, and there have been really great sessions both this year and in previous years that go over topics which are related to this talk.

For example, if you are very interested in profiling the GPU performance of your application, and if you are really, really, really excited to get your hands on that new GPU instrument, I would like to point you at the Metal Performance Optimization Techniques talk, which was given earlier today, where they talk about a whole bunch of different techniques that you can use to optimize your GPU work, not just if you are using Metal.

In addition, if Time Profiler is your jam, then you want to check out the new Profiling in Depth talk, which was given yesterday, which goes into a deep dive on how to use Time Profiler to get a great idea of what your application is doing.

And finally, if you guys are really interested in what is happening in the Core Animation and GPU stages of the pipeline we have discussed today, I would like to point you to the Advanced Graphics and Animation talk from last year's WWDC.

All of these talks and many, many more can be found on our developer portal at developer.apple.com.

I hope you learned a lot today and over the entire course of this week, and I hope you had an enjoyable WWDC.

Thank you.

[ Applause ]

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