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In this example we demonstrate how to use Velocity and Luminance to define a screen space image to control rasterization with VRS Tier 2. The shading rate buffer is a render target that is 1/8th or 1/16th of total render target size depending on IHV implementation. By computing luminance of an 8x8 or 16x16 tile from G-Buffer render target we can define a shading rate in the shading rate buffer based on a 'Just Noticeable Difference' calculation derived from both tile luminance and tile velocity.
- Sensitivity Threshold: Threshold for determining the “Just Noticeable Difference” Common values include 0.25, 0.5, and 0.75 (Quality, Balanced, Performance). Higher values mean lower image quality and higher performance.
- Quarter Rate Sensitivity: Increases the aggressiveness for the 4x4,4x2,2x4, shading rates, higher values means lower quality and higher performance
- Env. Luma: Global illumination value increases the overall LUMA during the “Just Noticeable Difference” algo. Higher values mean lower quality and higher performance.
- Use Motion Vectors: Enable to include motion vectors, you need to move around the scene to observe the behavior, there is a slight time cost when enabling this feature.
- Use Weber-Fechner: The default algorithm is an approximation but we can use a more precise algorithm known as Weber-Fechner, there is a time cost but comes with higher quality / precision. Test it in areas of high frequency content.
- Weber-Fechner Constant: It can probably help us dial in the Weber-Fechner precision but we haven’t tested it with values other than 1 in our testing.
- Debug: Shows Screen-space Debug Overlay
- 1x1 is rendered as clear,
- 1x2/2x1 are rendered in blue with a white/black tick mark to indicate a vertical shading rate,
- 2x2 is rendered as a green square,
- 4x2/2x4 are rendered as orange/red with a white/black tick mark to indicate a vertical shading rate.
- 4x4 shading rates are rendered in magenta.
-vrs Enables or disables VRS, both Tier 1 and Tier 2 on (default), off
-overlay Toggles the debug overlay on, off (default)
-rate Sets the Tier 1 shading rate 1X1 (default), 1X2, 2X1, 2X2, 2X4, 4X2, 4X4 if additional shading rates are supported
-combiner1 Sets the first Tier 2 shading rate combiner passthrough (default), override, min, max, sum
-combiner2 Sets the second Tier 2 shading rate combiner; defaults to override