Geometry-Aware Framebuffer Level of Detail Lei Yang Pedro V. - - PowerPoint PPT Presentation

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Geometry-Aware Framebuffer Level of Detail Lei Yang Pedro V. - - PowerPoint PPT Presentation

Sep 06, 2022 278 likes •682 views

EGSR 2008 Geometry-Aware Framebuffer Level of Detail Lei Yang Pedro V. Sander Hong Kong University of Science and Technology Jason Lawrence University of Virginia Motivation Expensive procedural shading effects Heavy pixel shader

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Geometry-Aware Framebuffer Level of Detail

Lei Yang Pedro V. Sander

Hong Kong University of Science and Technology

Jason Lawrence

University of Virginia

EGSR 2008

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Motivation

  • Expensive procedural shading effects

– Heavy pixel shader workload – Examples

  • Soft shadows

27fps

  • Ambient Occlusion

3.2fps

  • Procedural noise texture

120fps

  • …

2 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

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SLIDE 3

Motivation

  • A method for reducing pixel workload

– General – Lightweight – No preprocessing – Smoothly adjustable tradeoff between speed/quality

Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence 3

1x 2x 3x 5.6x 9x 11x Tradeoff Tradeoff

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Dynamic Resizing

  • Render scene to low-res buffer (1st pass), then

upsample to target resolution (2nd pass). [Montrym97] – # of original pixel shader invocation is reduced (∝ 1/r2) – Blurs geometric discontinuities

1st pass Original shader 2nd pass Upsample

4 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

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SLIDE 5

Geometry-Aware?

Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence 5

+ =

depth normal

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Related Work

  • Interleaved sampling [Segovia06, Laine07]
  • Image-based proxy accumulation [Sloan07]

Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence 6

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SLIDE 7

Related Work

  • Edge-and-Point render cache

[Bala03, Velázquez-Armendáriz06]

Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence 7

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SLIDE 8

Overview

  • Geometry-Aware Resizing
  • Fine-Grained Resizing
  • Automatic Framerate Control
  • Results and Demo
  • Discussions and Conclusion

Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence 8

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Our Approach

  • Geometry-Aware Resizing

– Upsample according to geometric similarities between lo-res and hi-res buffers – Two-pass technique

  • 1st pass: Render geometry with the original pixel

shader on low-res buffer, store geometric info (normal & depth) + color

  • 2nd pass: Render geometry at full resolution and

use geometry-aware kernel to reconstruct the shading from the lo-res buffer

9 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

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Geometry-Aware Resizing

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upsample color z n (z) depth (n) normal (z) depth (n) normal

1st pass 2nd pass

Vertex/ Geometry processing Pixel processing

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Geometry-Aware Reconstruction

Weight samples based on geometric similarity

1 1 1 1 0.1 0.9 0.9 0.9

Bilinear Bilateral

11 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

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Color sample j from the low-res buffer Filter weight of sample j Color sample j from the low-res buffer Filter weight of sample j

Joint Bilateral Filter

12 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

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Color sample j from the low-res buffer Spatial filter: bilinear / biquadratic / bicubic / Gaussian Color sample j from the low-res buffer Spatial filter: bilinear / biquadratic / bicubic / Gaussian

Joint Bilateral Filter

13 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

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Color sample j from the low-res buffer Range filter 1: Gaussian of the normal distance Color sample j from the low-res buffer Range filter 1: Gaussian of the normal distance

Joint Bilateral Filter

14 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

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Color sample j from the low-res buffer Range filter 2: Gaussian of the depth distance Color sample j from the low-res buffer Range filter 2: Gaussian of the depth distance

Joint Bilateral Filter

15 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

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Joint Bilateral Filter

16 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

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Joint Bilateral Filter

17 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

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Overview

  • Geometry-Aware Resizing
  • Fine-Grained Resizing
  • Automatic Framerate Control
  • Results and Demo
  • Discussions and Conclusion

Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence 18

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Fine-Grained Resizing

  • Resize only expensive & spatially smooth

computations

  • Break up the original shader

– Expensive & spatially smooth computation: 1st pass (at low-res) – Inexpensive / spatially high-freq computation: 2nd pass (at full-res)

19 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

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Fine-Grained Resizing

+ =

1st pass 2nd pass

20 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

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Comparison: Bilinear vs. Bilateral

  • Fine-grained resizing + Bilinear upsample?

Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence 21

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Overview

  • Geometry-Aware Resizing
  • Fine-Grained Resizing
  • Automatic Framerate Control
  • Results and Demo
  • Discussions and Conclusion

Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence 22

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Automatic Framerate Control

  • Dynamically select resizing factor r to

maintain a constant framerate

  • Use a feedback control mechanism
  • Input: previous frame-time
  • Output: r
  • Integral controller

23 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

Integral controller Reference frame-time 1st pass Original Shader 2nd pass Geometry-Aware Upsampler r Actual frame-time

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Controller Formulation

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  • 1. Pixel processing

time ∝ # of pixels

  • 2. Pixel-bound

Constant screen coverage

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AFC implementation

  • Limit the range of Δt, Δr and r
  • Experimentally determine K’ with the

maximum screen coverage

25 Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence

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Overview

  • Geometry-Aware Resizing
  • Fine-Grained Resizing
  • Automatic Framerate Control
  • Results and Demos
  • Discussions and Conclusion

Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence 26

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Results – Car

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Results – Car (con’t)

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Results – Chess

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Results – Chess (con’t)

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Results – Dragon

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Results – Dragon (con’t)

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AFC results

  • Experimental data:

– Over 1000 frames – Various outside disturbances

  • View changes
  • Screen coverage changes
  • Shader workload changes

Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence 33

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Overview

  • Geometry-Aware Resizing
  • Fine-Grained Resizing
  • Automatic Framerate Control
  • Results and Demo
  • Discussions and Conclusion

Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence 34

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Limitations

  • Resizing high frequency signal

– Popping and flickering artifacts (aliasing)

  • Undersampled fine geometry

– Missing details around regions with high depth/normal complexities – Recompute missing samples in a 3rd pass?

  • Added geometry processing overhead

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Practical Advantages

  • Multiple shader / objects

– Sharing the same resized buffer – Sharing the reconstruction pass – Allow unified AFC

  • Easy to apply

– Mainly an added reconstruction pass

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Conclusion

  • A general approach for reducing shading

costs

  • Respect geometric discontinuities better

than conventional resizing

  • Allow continuous adjustment of

error/performance tradeoff

  • Automatic framerate control
  • Straightforward to incorporate into

existing systems

Geometry-Aware Framebuffer LOD -- L. Yang, P. V. Sander, J. Lawrence 37

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Future Work

  • Multi-resolution resizing
  • Automated selection of resized elements
  • Resize for super-sample anti-aliasing
  • Obtain a Bosnia-Herzegovina visa ☺

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Questions?

10 r 1