SIGGRAPH ASIA 2011 Preview seminar Shading and Shadows

Shading and Shadows 1.Image-space Bidirectional Scene Reprojection 2.A Shading Reuse Method for Efficient Micropolygon Ray Tracing 3.Genetic Programming for Shader Simplification 4.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+1 Interpolated frame t+α Flow field

1 Image-space Bidirectional Scene Reprojection Scene-assisted interpolationImage-based interpolation Rendered t Rendered t+1 Rasterized t+α Rendered t Rendered t+1 Interpolated t+α Reverse reprojection at each pixel Displacement Scene flow estimation at each pixel Interpolated t+α No geometry infomation 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 Mutation 6.Selection for next iteration – same as Ranking and Diversity + asin bc * + a bc * mutation 1 st 2 nd 3 rd 5 th 4 th 6 th crossover Selection (random) 2 nd 4 th AST Replace by average Crossover 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 space2. Depth buffer min&max depth caster (triangle) receiver Shadow Buffer 4. Rendered image Shadow rasterization test against each plane of shadow frustum ←AABB shadow frustum 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

Shading and Shadows 1.Image-space Bidirectional Scene Reprojection 2.A Shading Reuse Method for Efficient Micropolygon Ray Tracing 3.Genetic Programming for Shader Simplification 4.An Efficient Alias-free Shadow Algorithm for Opaque and Transparent Objects using per- triangle Shadow Volumes