Breaking the Frame

David LuebkeUniversity of Virginia

Graphics Hardware 2005: Evolution or Revolution?

Frameless Rendering

Technique: [Bishop et al. 1994Implementation & Video [Parker et al. 1999]Codec: huffYUV [dll] [inf]

Graphics Hardware 2005: Evolution or Revolution?

Overview: What We’re Doing

• Spatio-temporally adaptive frameless sampling– Prioritize sampling towards regions of greater change

• Spatial change: edges• Temporal change: motion

• Reconstruction of resulting samples – A “deep buffer” stores samples in time & space– Reconstruct image at front edge of time: apply filter kernel

with varying width in space and time

Graphics Hardware 2005: Evolution or Revolution?

• Static scenes/regions– Old samples useful, use them to sharpen/antialias – Temporal width should dominate

• Dynamic scenes/regions– New samples useful, old samples stale– Emphasize new samples even if image is less sharp– Spatial width should dominate

Temporally Adaptive Reconstruction

“Traditional” frameless

Adaptive frameless

Adaptive Frameless Rendering [Dayal et al., EGSR05]

Video Preview

Graphics Hardware 2005: Evolution or Revolution?

Summary

• Better than traditional frameless rendering • Better than traditional framed rendering!

– Frameless = ungridded temporal sampling lower latency

– Samples when and where needed better images at low sampling rates

– Antialiases static regions by incorporating old samples lower error even than 10x sampling rate

• Still in simulation

Discussion: Asynchronous Graphics

• What if reconstruction was part of display?– Imagine display as systolic array of pixels– Input: stream of samples, not sequence of images

• Enables asynchronous parallel graphics– Parallel graphics frameworks share common constraint: must

ultimately combine all results into a single frame– Breaking the frame also breaks underlying assumption and

constraint in parallel graphics!• See SIGGRAPH Panel “The Ultimate Display”

– Punchline: Refreshing every pixel every time = Bad Idea

The End

Acknowledgements:OpenRT Interactive Raytracing ProjectBART ray tracing benchmarkStanford 3D Scanning RepositoryNational Science Foundation awards 0092973, 0093172, and 0112937

Graphics Hardware 2005: Evolution or Revolution?

Sampler Reconstructor

Controller

DeepBuffer

RayTracer

AdaptiveFilter Bank

DeepBuffer

samplessamples

varia

tion,

gra

dien

ts imag

elo

catio

ns

sample

s

tiling, view,gradients

Sampler Reconstructor

Controller

DeepBuffer

RayTracer

AdaptiveFilter Bank

DeepBuffer

samplessamples

varia

tion,

gra

dien

ts imag

elo

catio

ns

sample

s

tiling, view,gradients

System overview

static scenedynamic scene

Temporally Adaptive Reconstruction

static scenedynamic scene

Comparison: Traditional Frameless

Graphics Hardware 2005: Evolution or Revolution?

Discussion: Coherence

• What about coherence?– Frameless rendering implicitly gives up spatial

coherence, which is big win for fast ray tracers• Partially ameliorate with tiled structure, gradient rays• Might need to organize “random” samples around memory

– But we gain temporal coherence!• Fewer samples: needn’t resample everywhere every frame• Can we design a parallel architecture around this

temporal coherence?

Graphics Hardware 2005: Evolution or Revolution?

Comparison: Render Cache

• Probably most closely related approach– Sampling based on (framed) priority image

• Biased toward old & undersampled regions– Killing off old samples also biases towards age– Semantic “hints” age some samples quicker (e.g. specular surfaces)– Temporal response by aging samples if new one detects variance

• Error diffusion dither to place samples within image

– Image-space reconstruction via (non-adaptive) filtering• 7x7 “prefilter” followed by 3x3 Gaussian • Depth culling helps with occlusions

– See [Walter et al 1999]

Graphics Hardware 2005: Evolution or Revolution?

Evaluation: Mostly DynamicInteractive Animation 400k samples/sec

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RM

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rro

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400k Full Res

400k 60Hz

traditional frameless

Full Res 60Hz

adaptive no reprojections

adaptive

Graphics Hardware 2005: Evolution or Revolution?

Evaluation: Mostly Static

Toycar Animation 400k samples/sec

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0 50 100 150 200

#Frames

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rro

r