SIGGRAPH ASIA 2011 Preview seminar

Shading and Shadows

Shading and Shadows

1. Image-space Bidirectional Scene Reprojection2. A Shading Reuse Method for Efficient

Micropolygon Ray Tracing3. Genetic Programming for Shader

Simplification4. An Efficient Alias-free Shadow Algorithm for

Opaque and Transparent Objects using per-triangle Shadow Volumes

Image-space Bidirectional Scene Reprojection

　 Real-time temporal upsampling through image-based reprojection of adjacent frames

L. Yang, Y-C. Tse, P. Sander, J. Lawrence, D. Nehab, H. Hoppe, C. Wilkins

Rendered frame t Rendered frame t+1Interpolated frame t+α

Flow fieldFlow field

1

Image-space Bidirectional Scene Reprojection

Scene-assisted interpolation Image-based interpolation

Renderedt

Renderedt+1

Rasterizedt+α

Renderedt

Renderedt+1

Interpolated t+α

Reverse reprojection at each pixel

Displacement

Scene flow estimation at each pixel

Interpolated t+α

No geometryinfomation

t+α

Image-space Bidirectional Scene Reprojection

• Scene flow estimation

• Partial computation of I-frames

Event!Time lag...

Image-space Bidirectional Scene Reprojection

• Additional search initialization– Increasing accuracy– Dual initialization, Latest-frame initialization

• User study : simple game– To analyze effect on user and experience of the

tradeoff between the higher framerates and increased latency

Question- Enjoyed the game?- Game was responsive?- Animation was smooth?

Simple game

Genetic Programming for Shader Simplification

• GP for optimizing shader code– Mutation operation– Error metrics– Performance measure

• Advantage– Possibly better than manual

optimization

P. Sitthi-amorn, N. Modly, W. Weimer, J. Lawrence

Original shader

Simplified shader

Genetic Programming for Shader Simplification

1. Population initialization– Mutating original shader

2. Fitness evaluation– Timing and quality

3. Ranking and Diversity– Retain low-ranked variants

4. Mating selection– Tournament selection

5. Crossover and Mutation6. Selection for next iteration

– same as Ranking and Diversity

+a sin

b c*

+asin

b c*

mutation

1st 2nd 3rd

5th4th 6th

crossoverSelection

(random)

2nd

4th

AST AST

Replaceby averageCrossover

Swap

Remove

Add

Genetic Programming for Shader Simplification

• Error model– L2-RGB error / structural similarity index over frames– Sampling small patches on G-buffer (modify pix-shader)– Cross-correlation 0.84 (actual error - predicted error)

• Performance model– Sampling small patches on render target– minutes → 1-2 secs， cross-correlation 0.95 (error)

An Efficient Alias-free Shadow Algorithm for Opaque and Transparent Objects Using Per-triangle Shadow Volumes

• A shadow volume algorithm– Cast shadow– Point (& directional?) light

• Advantage– Screen-space anti-aliasing– Transparent shadow-caster &

receiver– Small memory footprint– No load-balancing issue– Deferred shading pipeline

E. Sintorn, O. Olsson, U. Assarsson

An Efficient Alias-free Shadow Algorithm for Opaque and Transparent Objects Using Per-triangle Shadow Volumes

Common shadow volume• Caster : silhouette edge

– Preprocessing

• Depth + stencil buffer • Hardware support• Opaque model

Proposed algorithm• Caster: each triangle

– No adjacency info.– No preprocessing

• Depth + shadow buffer• CUDA implementation• Compatible with screen-

space anti-aliasing, textured-shadow caster, stochastic transparency

Light Model

Caster

Caster =all faces

Shadow mapping• Resolution of shadow map• Aliasing

point light

camera 1. Clip space 2. Depth buffer

min&maxdepth

caster (triangle)

receiver 00000

0

000

00000

000

0

000

3. Shadow Buffer4. Rendered image

Shadow rasterization test against each plane of shadow frustum

←AABB

shadowfrustum

An Efficient Alias-free Shadow Algorithm for Opaque and Transparent Objects Using Per-triangle Shadow Volumes

111 1

An Efficient Alias-free Shadow Algorithm for Opaque and Transparent Objects Using Per-triangle Shadow Volumes

• Hierarchical depth buffer and shadow buffer

• Colored, transparent shadow-caster– Floating point value shadow buffer– Stochastically setting shadow bit

• Screen-space anti-aliasing (MSAA, CSAA, SSAA)– # of shadow bits & depth derivative

0110

1110

1110

0110

0 1 1 0

0 1 1 0

00

11

0 0 0 0

0

0

0

0

Shading and Shadows

1. Image-space Bidirectional Scene Reprojection2. A Shading Reuse Method for Efficient

Micropolygon Ray Tracing3. Genetic Programming for Shader

Simplification4. An Efficient Alias-free Shadow Algorithm for

Opaque and Transparent Objects using per-triangle Shadow Volumes