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Real-time REYES

Real-time REYES. Jeremy Sugerman. This Talk. Still exploring future GPUs, Direct3D / GL This time in a software context Offline REYES, as RenderMan, is king of the rendering world What would real-time REYES look like?

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Real-time REYES

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  1. Real-time REYES Jeremy Sugerman

  2. This Talk • Still exploring future GPUs, Direct3D / GL • This time in a software context • Offline REYES, as RenderMan, is king of the rendering world • What would real-time REYES look like? • Where are current GPUs / Direct3D and REYES the same? Similar? Different?

  3. Background • “The Reyes Image Rendering Architecture” • Pixar: Rob Cook, Loren Carpenter, Ed Catmull • SIGGRAPH 1987, First film 1985, Oscar 1993 • “An architecture optimized for fast high-quality rendering of complex animated scenes.” • Fast: feature-length film in a year • High-Quality: virtually indistinguishable from live action • Complex: as visually rich as real scenes.

  4. REYES Features • Primitives are smooth surfaces • Automatic, adaptive refinement • Programmable shading including displacement • On surface-space grids • Very high resolution geometry for visibility • After shading • Stochastic sampling in time, space, lens • Motion-blur, anti-aliasing, depth of field • Order-independent (depth sorted) blending • Wide pixel reconstruction filtering

  5. Multiple Primitives Bound Split Primitives Dice Primitives Unshaded Grids Shade Shaded Grids Bust & Bound Micropolygons Sample Visible Points Blend & Filter Basic REYES Pipeline Parallel scalability is added with screen-space bucketing computed during the Bounding and Splitting. Deferring Dicing also allows each bucket to be depth-sorted and occlusion culled.

  6. REYES on a GPU? • If you squint at it right… ‘Grids of micropolygons’ → ‘quads’ ‘Displace and shade’ → ‘shade vertices’(*) ‘Bust & bound, sample’ → ‘rasterize’(*) ‘Blend & filter’ → ‘blend & filter’(*) • Technically, OpenGL even includes implicit surface (NURBS) evaluators, but there is no serious support in (current) GPUs.

  7. Opaque GPU-REYES • Tesselate to grids in advance (CPU, cache, …) • Render grids as GL_QUADS • Displace, shade grids with a vertex shader • Cull, sample, and produce visible points with the rasterizer (MSAA / FSAA) • Reconstruction during ROP / FB • Flat fragment shading with micropolygons! • Current GPU lacking in tesselation, shading richness, stochastic sampling, blending

  8. GPU Mismatches • High level surfaces versus triangles • Surface vertex shading versus fragment shading • Including a constrained shading language • Stochastic sampling versus MSAA rasterization • Depth order versus primitive order blending • Note: REYES only tries to make ‘pictures’. • Bonus: Opaque REYES is totally unordered.

  9. Straightforward GPU Evolution • High level surfaces are already coming • Without ordering, performance is easy • Shading surface points versus pixels is fakeable • Less flexible GLSL/HLSL is fine • Unified shader cores help a lot • Adjust rast for small quad workloads • Stochastic sampling versus MSAA rasterization • Allow rast to time-sample linear motion

  10. Sticking Point: Blending • Primitive order blending generates poor images • Depth order risks unbounded storage needs • Samples must be buffered until all closer samples are blended. • Closest sample may not happen until the last grid of the last primitive. • Unbounded storage is anathema in GPU environments and real-time systems in general.

  11. Options for Depth-Order Blending • Classic REYES buckets grids into screen-space partitions. • Reduces, but still does not bound, footprint • Assume GPU REYES has fixed on-chip buffers • Three options when a bucket fills: • Rendering fails (awful) • Spill to memory (slow? when memory fills?) • Shrink bucket, discard samples newly outside (recomputation hard? too compute wasteful?)

  12. GPU REYES Summary • Unordered • Retained mode input (at least for blending) • Simplified shading language • Separate opaque and blended modes • Constrained reconstruction filters • Bound and split on CPU? Simplified adaptivity? • Mandatory displacement shader separation? • Constraints on stochastic sampling? • Blending policy– Primitive order? Spill? Shrink?

  13. Acknowledgements • Kayvon has provided explanation and discussion beyond a point where I can separate any ideas unique to myself. • Kurt and Pat provided excellent historical context and insight. • Gordon Stoll and Bill Mark repeated the word ‘REYES’ and insisted that its shading / anti-aliasing properties were valuable until I dug into it in self-defense.

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