Platform Porting: the BBC’s Turning Forest launches on Gear VR
Posted by Zillah Watson, Chris Pike on , last updated
The Turning Forest, a magical virtual reality fairytale, is now available on the Oculus Store for Gear VR - Samsung’s mobile headset. BBC R&D's Zillah Watson and Chris Pike and VRTOV's Oscar Raby and Katy Morrison write about the challenges of porting the experience between VR platrforms.
Originally only publicly available as a launch title for Google Daydream, Samsung Gear VR users will now also be able to experience the enchantingly surreal VR story, as they enter a magical forest and embark on an extraordinary adventure with a fantastical creature.
The Turning Forest was produced by BBC Research & Development in collaboration with virtual reality production studio, VRTOV - originally for the Oculus Rift. The new Gear VR version will enable viewers to trigger interactions by gaze, such as making music with the monster’s teeth, as well as the birds, fish, and icicles and other items that feature in the fantasy world.
It features an award-winning spatial soundtrack, to truly immerse viewers in this entrancing 360 degree world. The sound was adapted from an original soundtrack commissioned for S3A: Future Spatial Audio for an Immersive Listener Experience at Home, funded by the Engineering and Physical Sciences Research Council (EPSRC).
'Porting' the original Turning Forest VR experience — created for the Oculus Rift and driven by a powerful computer — to high-end mobile platforms like Google Daydream and Gear VR is no trivial task. It has revealed one of the current challenges of producing VR – ports to different platforms are essentially rebuilds. But with the Turning Forest we were also able to use the opportunity to improve the original experience, for example the composer Jon Nicholls reworked some of the music and recorded it with instrumentalists. And we added new interactive elements to the forest, such as birds.
Why are different ports so time consuming?
Currently different VR platforms have many different capabilities and feature sets. So porting from one platform to another often involves redesigning key functions of the project and sometimes re-building the project's components to make them appropriate to the performance capabilities of the new platform. Sometimes that can mean adding a new feature to take advantage of a capability that wasn't available in the original project (like adding a hand-based interaction because a new controller is available, for example). Sometimes it can mean scaling back on graphics, audio, or visual components that use a lot of processing power.
If your original project wasn't designed to run on lower-spec devices, you might have a lot of work to do in order to make it compatible. And if certain effects or functions were integral to your project and aren't available in the new platform, then you may need to be creative or do some significant redesigning. For example, if your original project was set in a foggy world which looked fabulous on a PC, what will you do when you want to make that run on a mobile phone that can't calculate thousands of fog particles? Or what happens if your original project's game-play relied on your player being able to look around corners (maybe you're a detective solving a crime), and then you want to move it to a mobile VR platform without positional tracking - how are you going to solve the loss of that feature? Rewrite your script? Give your player a mirror to use to see around the corner? Make them invisible?
For The Turning Forest, porting the project from Oculus Rift to Daydream to Gear VR meant simplification of many of the graphic elements in order to optimise performance from running on a gaming PC to running on a new mobile phone to running on a two-year-old mobile phone. We had to look at the number and types of particle systems we used and reduce these, reduce the number of polygons in the environments, simplify some of the shaders and reduce some of the real-time effects like shadows to avoid the load on the processor. Some of these changes altered the way the assets looked (the tree canopies for example are less complex in both the mobile versions than the PC version), but some are invisible to the user - we remade the creature body for example to reduce the polygon count, but it still looks very close to the way it looked in the original project.
We also incorporated a hand-based interaction when we ported the project to Daydream, which isn't present in the Gear VR or PC versions - these relied on a gaze based interaction. This involved some design work - exploring the differences in the way that users will move their hands as opposed to their heads and trying to align our interactive objects to that motion. We also had to work out how to represent the controller within the world - did it look like a controller or more like something that belonged in the world? Without rewriting the narrative our solution was to turn the controller into a leaf, and to add in sound effects that were linked to a trail of leaves blowing in the wind that you controlled via your leaf-controller.
Audio
The way the sound was rendered in the Oculus Rift version processed each sound source individually which was too processor heavy to work on a mobile. Instead we used ambisonics, an intermediate spatial audio format based on spherical harmonics. This simplified the set of roughly 60 audio objects down to a 16-channel representation of the audio scene by a pre-rendering process. BBC R&D’s custom audio rendering code was replaced with the Google VR SDK to process the audio in real-time on the mobile device. We had to make some adjustments to the sound mix to make it work, but we used the same audio SDK for the Gear VR versions which made the sound relatively simple to port later on.
Ambisonics is also the basis for spatial audio on YouTube and Facebook 360 audio. We also worked on the interactive music elements of the experience using the Daydream controller and gaze interaction for the Gear VR.
This project is informing the process for release of other VR apps from the BBC. And the audio tools that we have created are now being used for other productions, including Planet Earth 2.
Tips if you are considering making different versions
- Make a plan for subsequent versions or platforms before you start to build your first version.
- Think about all the places you're likely to want to distribute, and the key differences between those platforms (one controller, two controllers, no controller, differences in spatial tracking etc) and build that into your project design.
- Be mindful that if your project relies on a visual or sound design loaded with effects that perform great on a PC, then you're going to have to get creative if porting to mobile.
- It’s easier to go from mobile to PC than the other way around.
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More on Virtual Reality and 360 Video:
BBC Media Centre - BBC’s virtual reality fairy tale launches on Gear VR
BBC Connected Studio - Watch 20 minute talks from our experts on Virtual Reality and 360 Video from #BBCVR day
BBC R&D - Factual Storytelling Tips for 360 Video
BBC News Labs - 5 Lessons in VR
BBC R&D - 360 Video & Virtual Reality
BBC R&D - Why is BBC R&D interested in Virtual Reality?
About the BBC - Exploring VR and immersive video
BBC R&D - Virtual Reality Sound in the Turning Forest
BBC R&D - A Virtual Reality Fairy Tale Premiered at Tribecca Film Festival
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