Field of view in the Oculus VR

User Pogo on the Oculus VR forums asked the other day about why some applications didn't cover more of the available screen real estate on the Rift, and consequently occupied a smaller field of view than was possible.

Every pixel on the Rift display has a fixed relationship with the lenses (discounting the slight differences between the three sets of lenses that come with the Rift).  Each pixel has a specific θ (pronounced theta) which represents the angle between the lens axis and the line from the pixel through your eye.  Each pixel also has a specific 'perceived θ', which is the perceived angle between the lens axis and the where it appears to be because of the lens distortion.  

What this means is that if you're drawing on a smaller area of the Rift screen, you're essentially providing a smaller field of view.  

As an example of the issue Pogo posted the following images.  The first is from the Oculus configuration utility used to test the IPD and height settings a user has entered.

The second is from the lauded RedFrame environment demo.

And the last is from Half Life 2.  

All three applications are using native Rift support, but are rendering different fields of view.  But why?  Well, there are a number of reasons that this might happen.

Understanding the Oculus Rift Distortion Shader

As much as any other single thing, the distortion shader is the heart of what makes the Oculus Rift possible.  It's enabled by incredible advances in computer rendering technology that have been driven by both the computer gaming industry and the movie and television entertainment industry.  Only in the past few years has the rendering power to apply fairly complex calculations to every single output pixel of a rendered frame has become ubiquitous enough that a product like the Rift could become possible.

Part of finding new applications for the Rift will come from a detailed understanding of how the whole system works.  For many, it's enough to be told that it's done with lenses and software the corrects for the lens distortion.

A more detailed understanding can be useful though, especially when you're trying to make something render properly and having trouble with the distortion shader and it's settings.