Hey guys and gals!

Following last week’s post, which introduced some basic VR concepts, I thought I would do the same but oriented toward Unreal Engine 4. Since the engine went free a few weeks ago, I bet there are a lot of newcomers who could use a hand! So without further ado, let’s delve into the subject.

THE UNREAL EDITOR AND VR

There are a lot of ways to preview your content in Unreal, two of which are particularly helpful for VR. The Play mode can be found in the toolbar above the viewport in the standard Unreal layout.

VR Preview:

This Play mode starts the game in VR mode directly inside the editor. This is new in Unreal 4.7 and is very useful to actually have HMD data inside the editor to debug (in blueprints, for example). This Play mode works well with the Oculus’ Direct to HMD, but it seems to have some issues in extended mode.

Standalone Game:

Prior to 4.7, this was the way to test your VR content. Pressing Alt+Enter starts the stereo rendering. We still use it to profile using Intel GPA. More on our usage of Intel GPA in another post!

World to Meters:

In the World settings, this value is under the VR category. This is the representation of Unreal units to real-world meters. 100 means that 100 Unreal Units equal 1 meter in real life. For FATED, we played a bit with this value to get the proportions we needed. It is recommended to set this value so that it fits with the real-life measurement of your in-game objects.

Head Mounted Display Blueprint Nodes:

There are a lot of exposed methods to do logic directly inside blueprints. This category should be the first place to look for HMD-related functionalities.

Use Less CPU in Background:

You want the editor to stop most of its processing when testing your content. This option can be found under the Editor Preferences in the Miscellaneous section.

Scalability Settings:

I feel like I’m repeating myself, but performance is critical in a VR game! Unreal Engine 4 comes with a great scalability features that can help create the range of performance for your game, from your minimum specs to your recommended specs. More on this in a performance post I’m planning to write soon.

COMMAND LINE FUN!

If you’re already familiar with Unreal development, you know about the console and all the commands that can be entered through it. This is also true about the HMD Interface (Head-Mounted Display). Most of these commands are accessed with the “hmd” keyword; here is a list of the ones we use the most in FATED’s development.

hmd stats:

This command displays info about your HMD. A lot of the stuff I’ve mentioned in my previous post can be seen here. Your current latency, whether positional tracking is activated, whether the camera is detecting the HMD, etc. There is also information on Time Warping, and whether the engine is updating the HMD info in the render thread. These are techniques to reduce latency that come right out of the gate in Unreal 4, making it a top-of-the-line choice for VR development.

hmd sp YYY:

YYY must be replaced by a number between 30 and 300. This is one of the easiest performance boosters at the expanse of visual quality. To create a better-looking picture, Unreal scales the image before the distortion process, sampling down afterwards to fit your HMD screen. By default it is at 135, but you can easily bring it down to 100 for better performance. It does look better at a higher percentage, though!

hmd vsync on/off:

Deactivating vsync can be useful to track your actual framerate.

stat unit:

Figure out if you are render thread-bound or GPU-bound. For FATED, we are pretty much always GPU-bound.

stat fps:

Are we running at 75 fps?

stat scenerendering:

This will show useful information about the scene’s rendering. You want to keep an eye on the number of draw calls, for example.

show YYY:

The ‘show’ commands are useful to hide some elements of your scene to try and figure out how much each of these elements takes to render. ‘Show staticmeshes’ and ‘show postprocessing’ are two examples of commands we used in early profiling.

profile GPU:

This will launch the Unreal Engine GPU Profiler. You can also do this at any time by pressing [Ctrl+Shift+,]. This is a good one to know about, as it is the first tool you will want to use for GPU performance profiling. It is kind of limited (and the reason we are using Intel GPA for deeper profiling), but it will point out some of the costlier effects in your scene.

These are the most useful ones for us, but go digging in there and you’ll find plenty other commands that are useful.

In my next episode of the FATED blog…

That’s it for now! Next time, I will talk a bit more about performance and how we got FATED running on a “normal” rig while still retaining great visuals!

Meanwhile, don’t hesitate to comment or ask a question; we’ll be happy to discuss with you guys!

Hi, my name is Michaël Dubé, Lead Programmer on the awesome FATED project!

Starting a new project is always thrilling and frightening at the same time. Venturing into virtual reality using a completely new technology, Unreal Engine 4, was something we were mostly excited about, though. Everyone on the team was super hyped for this project (and VR in general), which made the terrifying parts (hello performance!) not so terrible to bear.

Nevertheless, we learned a lot of really neat stuff during our first months of development, both about UE4 and VR, and my hope is for this blog to be half an entertaining view of the development of our game, and half a chronicle of all the blood and tears we shed to get there. It’s a Viking game after all; you can’t expect it to be all unicorns and rainbows!

For this first post, I wanted to keep it simple and talk about some basic but important virtual reality terminology, along with some tips on getting your rig ready to rock this new reality.

VR VOCABULARY

There are a lot of technical terms that come with VR development; I wanted to recap some of those and what they mean for FATED.

LATENCY
Basically, this is the time gap between your movement and its replication on-screen. You will often hear the term ‘motion-to-photons latency’ to talk about that. Low latency is very important in VR, as it is considered a major factor in reducing the effect of the infamous simulation sickness.

SIMULATION SICKNESS
This is what you absolutely don’t want the user to feel! This is similar to motion sickness (reading in a car) or sea sickness. Research still haven’t pinpointed what exactly causes this, but everything points to cognitive dissonance. As soon as you make the user experience something he doesn’t do in real life, there is a chance it will trigger simulation sickness. The Oculus Best Practices Guide is a great place to get info on the dos and don’ts.

http://static.oculus.com/sdk-downloads/documents/Oculus_Best_Practices_Guide.pdf

RESOLUTION AND THE SCREEN DOOR EFFECT

“The ‘screen-door effect’ […] is a visual artifact of the projection technology […] where the fine lines separating the projector’s pixels become visible in the projected image.”
http://en.wikipedia.org/wiki/Screen-door_effect

This is one of the reasons the consumer version of the technology will need better resolution. However, for developers this means that we have to take extra care when it comes to performance. We got great performances tips we applied for FATED that I’m eager to share with you!

REFRESH RATE
This is the frequency at which the screen refreshes. The DK2 is set at 75 Hz, so basically we need to update the screen at a constant 75 frames per seconds to get the best result. In VR, it is of the utmost importance to keep a steady framerate. Unless you want to make your players sick, that is (which we don’t, we swear!).

PRESENCE
This is what VR is all about! This is basically tricking your brain in thinking it’s really in your game. We are designing with this principle in mind to create mind-blowing and/or powerful moments for the players to experience. FATED is all about making the player live a meaningful and poignant adventure. Because of this alone, I strongly believe VR is the next step in the narrative medium.

http://static.oculus.com/connect/slides/OculusConnect_Epic_UE4_Integration_and_Demos.pdf

HARDWARE TIPS

Installing the Oculus Runtime is as simple as it gets, but there are some important settings that every VR enthusiast should be aware of.

RIFT DISPLAY MODE
What Direct to HMD does is ensure that the application is synced to the actual refresh rate of your Rift. It also helps reduce latency since the step of going to your desktop is bypassed. While I prefer the simpler Direct to HMD, we are still using the Extended Display Mode on FATED for debugging purpose (more on that in another post!).

OCULUS CONFIGURATION UTILITY
This is where you can setup some information about yourself to get a better experience. Developers can then use this information to adjust the experience so it better fits the user, like adjusting the camera position using your IPD (interpupillary distance – the distance between your eyes).

BEWARE OF THE NVIDIA CONTROL PANEL!

If you have an NVIDIA card, chances are you can get a huge performance boost (we definitely saw a difference on some cards) by doing two simple things in the NVIDIA Control Panel. You should of course have the latest drivers before doing that.
First, in the Manage 3D Settings, there is a “Virtual Reality pre-rendered frames” setting that is set to 1 by default. You want to set that to “Use the 3D application setting”. Also, you will see “Power management mode”. Set that to maximum performance.

Next, you may want to go in your PC’s Control Panel, in the Power Options, and set your minimum processor state to 100%.

The above settings were part of changes I did for FATED when we encountered a problem known on the Unreal forums as the ‘37.5 fps lock’. This lockdown would normally happen if the frame rate drops below 75 frames per seconds, but this was not the case for us and some other developers. Some Oculus staff was involved in pointing this out, and this may not be necessary anymore once the consumer version is ready, but it definitely helped for FATED.

Well, that’s all for now. Obviously, there is a lot more to VR, and we will keep adding interesting content to this blog. In the meantime, if you have great tips to share with us or if you have any questions, we’d be happy to hear you out in the comments!

Stay tuned for more on FATED!