VR distortion correction methods

2
votes

I’ve read this article http://www.gamasutra.com/blogs/BrianKehrer/20160125/264161/VR_Distortion_Correction_using_Vertex_Displacement.php about distortion correction with vertex displacement in VR. Moreover, there are some words about other ways of distortion correction. I use unity for my experiments(and try to modify fibrum sdk, but it does not matter in my question because I only want to understand how these methods work in general).

As I mentioned there are three ways of doing this correction:

  1. Using Pixel-based shader.
  2. Projecting the render target onto a warped mesh - and rendering the final output to the screen.
  3. Vertex displacement method

I understand how the pixel-based shader works. However, I don’t understand others.

The first question is about projection render target onto a warped mesh. As I understand, I should firstly render image from game cameras to 2(for each eye) tessellated quads, then apply shader with correction to this quads and then draw quads in front of main camera. But I’m afraid, I’m wrong.

The second one is about vertex displacement. Should I simply apply shader(that translate vertex coordinates of every object from world-space into inverse-lens distorted & screenspace(lens space)) to camera?

p.s. Sorry for my terrible English, I just want to understand how it works.

1
unity3dshadervirtual-realitydistortion

1 Answers

0
votes

For the third method (vertex displacement), yes. That's exactly what you do. However, you must be careful because this is a non-linear transformation, and it won't be properly interpolated between vertices. You need your meshes to be reasonably tessellated for this technique to work properly. Otherwiese, long edges may be displayed as distorted curves, and you can potentially have z-fighting issues too. Here you can see a good description of the technique.

For the warped distortion mesh, this is how it goes. You render the screen, without distortion, to a render texture. Usually, this texture is bigger than your real screen resolution to compensate for effects of distortion on the apparent resolution. Then you create a tessellated quad, distort its vertices, and render it to screen using the texture. Since these vertices are distorted, it will distort your image.