The backstory

Those of you that haven’t devoured our various developer interviews might not know that Infinite Flight was originally developed for Windows Phone in 2011. There are a few reasons why we decided to target Windows Phone, but mainly it was because we were more familiar with the Microsoft development environment back in those days. This made it easier to ship the first version quickly.

On Windows Phone, we used XNA as our graphics API, since this was the only choice. XNA was a framework that allowed game developers to target Windows PC, Windows Phone, and Xbox with minimum code changes. Yes, we had a development version of IF running on an Xbox 360!

Unfortunately, XNA was deprecated and not long after, so was Windows Phone.

Thankfully, we started working on an iOS version sometime before that, but in order to not have to recode everything, we used MonoGame which is an XNA implementation for many platforms. On iOS (and Android), MonoGame uses OpenGL ES as the low-level graphics API.

Here’s where we are now

Unfortunately (again), OpenGL ES has been deprecated on iOS devices and Apple recommends using Metal; a more modern low-level graphics API. OpenGL ES still works but it is stuck at an old version with limited features and there is no telling if it will continue working indefinitely (deprecating things is Apple’s favorite).

There are many features we want to do in Infinite Flight that are very complex to implement with the limited feature set we are stuck with.

The only way for us to move forward is to overhaul our rendering backend to be able to take advantage of the newer graphics APIs (Metal on iOS and Vulkan on Android).

This is a pretty complex task that requires a lot of engineering time and won't result in any immediate visual benefit to the end-user. If all goes well, you won't notice anything! The main benefit will be performance; Metal and Vulkan are much more "low-level" than OpenGL ES, meaning they have less processing overhead and are more predictable. This should result in us seeing better frame rates and fewer "stutters" overall. Another benefit will be that it will unlock many possibilities for our developers to implement some cool new features.

Some features we'd like to implement but have been either impossible or too performance-inhibitive are things like:

• Dynamic lighting: the ability to have aircraft lights (airport lights, and more) illuminate the environment dynamically
• Improved aircraft shading that takes into account light coming from the environment around it
• Realtime shadows
• Volumetric effects like dense 3d clouds and better fog
• Texture streaming improvements to allow more visible aircraft in multiplayer

Of course, an update like Project Metal isn’t trivial. A lot of work is going on behind the scenes to make this happen. Our developers are hard at work laying the groundwork for the move to these updated graphics APIs. It doesn’t mean other work is being abandoned. Work on the B777-200 is moving along at a great pace, as is work on implementing clouds.

Ultimately these changes are great news for Infinite Flight users, even if they aren’t immediately visible. As always, we will keep you updated as we go along.

Our job is to prepare the data for streaming and make sure that it gets to your device as fast and as reliably as possible. Let’s dive into some Infinite Flight tech and look at how we do that.

Quad Spheres

In Infinite Flight, we use a "quad sphere" to partition our data. Flat earth people, this bit is as close as we'll get to siding (get it?) with you.

To prepare our scenery data for streaming, it is first projected to each face of a cube in a way that minimizes distortion (projecting a sphere to a 2D representation always creates some distortion).

In our case, face 0 is the one that contains Africa, face 1 contains Australia and sections of Asia, face 2 is mostly the Pacific Ocean, face 3 is the Americas, face 4 is the top (containing most of Europe, Russia, and the North Pole), and face 5 is bottom.

Data in each face is then split further in tiles using a quadtree structure. At level 0 of the quadtree, we have 1 tile representing one whole face of the cube, at level 1 we have 4 tiles, at level 2 we have 16, and so forth. For example, our 15m/px imagery data is split up to level 11, which represents a maximum of 4,194,304 tiles per face.

Partitioning it in this way helps to reduce the amount of data we need to fetch in order to display the scenery around the aircraft. As you fly, we only fetch the visible tiles based on their distance to the camera. For closeup terrain we will fetch the highest level tiles. For distant terrain we fetch the lower level ones since we don't need as much detail there until we get closer to them.

Caching

Since we have users connecting from all over the world, it is essential that requesting a tile is fast regardless of where they are. Our tiles are in a server cluster (multiple servers that share the load) located in the US, but are cached all over the world by using a CDN (Content Delivery Network).

When a tile is requested, that request first goes to a CDN server that is physically close to you. If it is the first time this CDN server sees this exact request, it will download the tile from our server cluster in the US, cache it locally and send you the tile. If the tile was requested recently by someone else in your region using Infinite Flight, then the tile is already in the cache and will be sent to you right away, without having to request it from our servers. Depending on your physical location, a tile request could take a few hundreds milliseconds to complete if it is not cached. If the CDN server closest to you already has a copy of the tile, that same request usually completes in less than 10 milliseconds.

Our CDN provider has a network of 150+ servers located all around the world, ensuring that scenery streaming is fast and reliable no matter where you are using Infinite Flight from. It's important to note that we also cache the scenery tiles locally on your device. The local cache has a maximum size of 512MB at the moment, and will automatically delete tiles that haven't been used in a long time when you reach that limit.

At the time of this post being published, our CDN saw more than 2 billion requests and delivered more than 70 TB of data in one month. That's 64.5 million requests per day, 2.6 million requests per hour, 44,800 requests per minute, and 746 requests per second. Roughly! We are always looking for ways to deliver higher quality and more content, while minimizing the requests required to the servers.

Of course all of this streaming comes at a cost. A frustration for some users is the cost of a Pro subscription to Infinite Flight. As you can see, as the number of users increases, so too does our cost to deliver content to those users. We are charged with finding the balance between serving quality content quickly, adding new streamable features such as aircraft (and one day other 3D objects), and keeping costs down.

With this post, we want to offer more transparency and context for what it actually means when we release "performance improvements" with a new update.

When building a mobile app there are 3 main aspects that need to be optimized: memory, cpu, and power usage. Infinite Flight also makes heavy use of the GPU (Graphics Processing Unit) but we will leave those details out for a potential future post.

Device Memory

Device memory limitations can pose a conundrum for our developers as they work to squeeze new features into an already feature-rich app. Memory, or RAM, (which differs from type of storage that allows you to save photos and apps) refers to an amount of data storage that Infinite Flight can use to complete tasks. If the app tries to use more memory than the device has available, it will likely result in a crash.

"Textures" are usually what use the most memory, both in terms of capacity and bandwidth. Between the terrain imagery and the aircraft liveries, Infinite Flight uses a lot of them, especially with recent aircraft. Most textures are streamed (downloaded from our servers) and loaded as you fly which requires some careful considerations to maintain a good frame rate. This is actually an area that we are looking at improving since currently there can be a noticeable "stutter" in situations where a lot of aircraft are being loaded at the same time in multiplayer.

Processing Power

Device processing power is—to put it simply—the rate at which a processor can perform computations. The clock rate, usually in GHz, indicates how many "cycles" a CPU can perform per second. A 2GHz processor can perform 2 billion cycles per second. Each operation, such as reading from memory, writing to memory, multiplication, addition, and so on, costs a certain number of cycles. This varies depending on the type of processor.

In the context of Infinite Flight, if we add all of the cycles from all of the operations it performs, multiply it by the frame rate we want (30 or 60 fps), that number needs to be under 2 Billion to ensure it runs smoothly on a single 2GHz processor. Easy, right? This might sound like a lot of headroom, but consider that a single main memory read can take hundreds of cycles. It is very important to optimize those, and reading from storage is even slower. In addition to this, we must account for the operating system, and the apps that are running in the background on the device as well.

To add more complexity to the matter, mobile processors often lower their clock rate, known as "throttling", to maintain a certain temperature and power consumption budget. In short, the more cycles an app uses, the slower the processor might get, so it is very important to be very efficient. This is especially true with memory read/write since they usually uses the most cycles.

Battery Power

As mentioned already, power consumption comes down to how many cycles an app uses. It is important to do as much as possible in as few cycles as possible. Memory access is one of the most costly operations in a processor. Optimizing those is key to good performance.

To give you a sense of what a memory access means in terms of performance, let's bring everything to a human scale and consider a very slow processor where 1 cycle takes 1 second. In our hypothetical processor, reading from main memory would take anywhere from 4 to 12 minutes. Reading from storage would take from 15h to 2 days. Requesting a scenery tile from our server would take 6 to 9 months. As you can see, it is crucial to always make sure to optimize for memory access. Thankfully, processors have a few layers of caches that can make those operations much faster if carefully taken into account.

It is all connected

Now that we have briefly explained the various aspects of performance optimizations, let's go through a concrete example.

Our recent aircraft are made of hundreds of thousands of polygons that we need to display at a minimum of 30 frames per second, including animations, shading, etc. In multiplayer, there can be many of those aircraft in view so it is not uncommon to have 1 million+ polygons that are potentially visible, just for the aircraft. The fastest way to draw something is to not draw it at all; when an aircraft is a few hundred meters away, there is no need to draw the interior since it won't be visible (we actually use its size on screen to determine this since we want those details to appear when zooming as well, not only when getting closer).

All of our recent aircraft have multiple levels of detail (simplified versions of the aircraft) that we pick based on its size on screen. This allows us to save some precious CPU/GPU processing power as well as memory bandwidth which results in decreased battery consumption. Those LODs are part of what our artists need to create when making a new aircraft and can be quite time consuming.

Conclusion

There is a lot going on behind the scenes that are often summarized by "performance optimizations" in our release notes. While not being what our audience cares about the most, it is what enables us to push Infinite Flight forward and make all the other features possible.

We see lots of room for improvement for Infinite Flight in spite of the challenges ahead. As devices continue to evolve and as our developers continue to push the boundaries of what's possible, we're confident our user experience will only get better as well.

We are happy to announce the next release of Infinite Flight will be available for download in the next 24h for both iOS and Android users. With this update comes a great list of improvements and additions.

• Brand new Bombardier CRJ-700 series with 13 new liveries
• New CRJ-700 wheel steering and suspension animations
• New user grade screen, which shows more information about how your grade is calculated

CRJ 700

We have built the CRJ-700 from the ground up with new textures, animations, and flight physics models. With these changes also comes several brand new camera angles! You wanted cabin window views; you got ‘em. Our new cabin model includes window views, and mood lighting. Need more flight deck cameras? No problem. We’ve also added some new animations to the main door, service door, and cargo doors, as well as windshield wipers. Your flight experience can be more real than ever as you push back in the CRJ-700 for your next regional flight!

*Note that the CRJ 900 and 1000 will be coming in the next few months for Pro subscribers and the CRJ-200 will be updated and remain free.

Grade Window Improvements

You will notice some changes to the way your experience grade is shown in the app. We don’t want your grade calculation to be a mystery so we’ve made some improvements to how this is displayed.

New satellite imagery (in case you missed it)

Last month we released new satellite imagery adding about 30% more 15m coverage to our global database. Check out the full post!

In-App Purchase Changes

In an effort to simplify our pricing model, we have now made all paid planes part of the Pro subscription. Moving forward we decided to move away from In-App Purchases for our aircraft the same way we did for scenery when we first released global. All "paid" aircraft are now only available through our Infinite Flight Pro subscription.

Note: If you have purchased aircraft in the past, don’t worry. You’re grandfathered in, and those aircraft will remain available to you whether or not you have an active Infinite Flight Pro subscription.

There are a couple of reasons for this change:

• It greatly simplifies our process to release new content on both Android and iOS, even allowing us to release new aircraft without requiring an app update.
• It allows us to allocate more resources to update older aircraft; we ultimately want to bring our entire fleet to the same level of quality you are now all expecting.

We understand that subscriptions are not for everyone. However we believe it is the best option for something like Infinite Flight, which continues to evolve and improve through the years.
You can stop at anytime, and when you decide to check out the new stuff, you get access to everything for a month for only $9.99.

Of course, we’re not done yet! We’re excited to show you more as we continue to build and improve Infinite Flight!

Happy landings.

We have been hard at work over the past few months to continue improving Infinite Flight.

Today we are pleased to announce that we are expanding our existing 15m imagery coverage. The new dataset contains ~500GB of new imagery (around 30% more coverage).

The best thing is that it is available now, with no bulky download necessary, at no cost to all our Infinite Flight Pro Subscribers. All you need to do is relaunch Infinite Flight and start flying from/to those newly covered regions (you might have to clear your scenery cache in Settings -> General -> Clear Cache).

Here are the main changes:

• Africa is now 100% covered
• Russia coverage is almost complete
• Madagascar + Indian Ocean islands are now covered.
• Many islands in the Pacific Ocean are now covered.

In order to give you an idea of what changed, below is the current coverage area compared to the new one:

Current 15m coverage:

Updated 15m coverage:

Some pictures of the new areas:

We should be able to add the rest of the world (including South America) by the end of the year. The regions that we don’t have yet are usually regions with heavy cloud cover that are harder to process.

Note that we also updated our Navigation Database and added the new content from the Airport Editing Team.

We hope that you enjoy this update as much as we do! As always, take a second to rate the app if you haven’t already.

One more thing…

As you know, we have been working on a new CRJ. Its release is taking longer than expected due to the higher quality standard we have adopted for our upcoming aircraft.

We have many performance issues to solve before we are able to add this “new generation” of aircraft to Infinite Flight and ensure a good experience on all devices.

In the meantime, we have been developing a couple more aircraft. We actually have a very small teaser for one of them showing one aspect of the new level of quality you can be expecting (I am sure you will quickly recognize what aircraft it is):

We can’t wait to show you more!

Happy landings.