Multi-resolution shading

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Multi-resolution shading or multi-res shading is a VR rendering technology part of the Nvidia's GameWorks VR. In multi-res shading, the rendering accounts for the distortion caused by the lenses of the HMD. The center of the image, an area unaffected the distortion, is rendered at high resolution than the edges of the image, where distortion occurs. Multi-res shading improves performance without sacrificing image quality.

Normally, an image on a screen, rendered by GPU, is flat. In an HMD, users view the image through lenses that allow the users to focus and increase field of view. When viewed from lenses, a flat image is greatly distorted. To counter this, the VR runtime software has to perform an extra process to "de-distort" or warp the image before it is passed through the lenses and onto your eyes. Because of this warp process, the edges of the image are compressed and have fewer pixels. Multi-res shading does not render the entire flat image. Instead, it renders the warped image directly, saving the processor from rendering a significant number of pixels.

Multi-res shading performs this function by diving the image into a grid with 9 viewpoints. Only the center viewpoint is rendered in full resolution. It renders the outer viewpoints at lower resolution because they merge and shrink during the distortion process. Multi-res shading improves the performance of the VR app by rendering fewer pixels.

Multi-res shading should be used by a game engine developer. It cannot be turned on from the driver directly.

According to Nvidia engineer Tom Peterson, multi-res shading can save about 50% of the pixel load.[1]

References

  1. https://www.youtube.com/watch?v=88RnIVcvuRY

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