Implementing a modern, RenderMan compliant, REYES renderer

Implementing a modern, RenderMan compliant, REYES rendererDavide Pascaribtools.com(contact: davide<at> ribtools.com)1

About REYESReyes or REYES (Renders Everything You Ever Saw)A flexible renderer, developed by Lucasfilm CG div. (“Pixar” from 1986)First used in 1984 in Start Trek II..still used today in Pixar’s Photorealistic RenderMan2* Images, from top, are copyright of Paramount Pictures and Pixar (subsidiary of The Walt Disney Company)

RenderMan compliant ?Defines a renderer with some basic capabilities such as:A RenderMan graphics state machineHidden surface eliminationPixel filtering and anti-aliasingUser programmable shadersTexture mappingEtc…3

REYES featuresNative support for high level surfacesDynamic LODCompact representationSubdivide per-frame based on size on screenDisplace geometry from texturesHigh quality filteringEasier to deal with translucency, motion-blur, etc.Can be used together with ray-tracing4

Split (1)A parametric surface: P = f(u,v)Split until “small enough” size (estimated) on screen6

Split (2)Calculate the bounding box in screen-space…test against predetermined max screen areaHere, the bounding box is too large..7

Split (3)When too large, split the patchIt’s easy with parametric primitives:Pnew = f(unew, vnew)New split points8

Split (4)Calculate the bounds of the new sub-patchesStill too large9

Split (5)Split recursively until every sub-patch is “small enough”…Small enough.. this isready to be diced10

What’s “Small Enough” ?When most sub-patches fit in a single bucketWhen dicing(see later) produces a suitable number of samples (sweet spot for performance)Sub-patch insidea single bucketOptimalSub-patch touchestwo or more bucketsNot OptimalA bucket11

DiceSmall enough sub-patches are dicedGenerate a dense grid of samples (1 pixel-per-sample or more..)1 pixelSmall enough n_samples <= max_samplesmax_samples is set for performance reasonsand to avoid distortion12

DisplaceApply a displacement shader to the position of the samplesmyDisplace(){ mag = texture( “dispmap” );P += normalize(N) * mag; N = calculatenormal(P);}13

ShadeApply surface and light shaders to get the colormyShader(){ txcol = texture( “pigment” ); Ci = diffuse(N,txcol);Oi = 1;}14

Sample – the micropolysForm virtualmicropolygons at the grid samples1 pixelVirtual micropolygons15

Sample – sample pointsMultiple sub-samples at every pixel…choose a sampling method: regular, multi-jittered (as shown), etc.16

Sample – gather samplesSamples get the color of the micropolygons they touch…each sample can have many values if the mpolys are translucent !17

Sample – convolutionMix the samples together……choose a filter: box, triangular, Gaussian, Sinc, etc..18

Sample – final pixel colorThe resulting “average” color is assigned to the pixel…repeat for every pixel 8)19

RibTools: A RenderMan-style renderer R&D20* Killeroo model from headus Ltd., used with permission.

RibTools’ key featuresRenderMan compliant(…almost (^^;))Parse RIB scene filesC-like shaders compiler and VMParametric surfaces, etc.Sub-pixel displacement mappingOpen Sourced (BSD License)Multi-threadedNetwork-distributed“Future proof” SIMDScalability !21

Distributed bucket renderingMulti-core CPURemote serversA frame is subdivided into discrete buckets

Buckets are assigned to threads on the CPU or to remote servers via TCP/IP

Geometry, shaders and textures are also transferred via TCP/IPWorks today !…it’s only a start. Needs optimizations, esp. network...............22

Shader systemA shading system is an essential part of a rendererShader.slShader.rrasmmyShader(){ txcol = texture( “pigment” ); Ci = diffuse(N,txcol);Oi = 1;}RSL Compiler__main:mov.vv $v4 N normalize $v5 $v4mov.vv $v6 $v5mov.vv $v3 $v6mov.vv $v7 Ifaceforward $v8 $v3 $v7 […] High-level C-like RenderMan shaders are compiled into custom RRASM assembly

RRASM is assembled and executed by the ShaderVirtual Machine (VM) when renderingShader VM23

Shading and SIMD (1)Values in a grid are treated as arrays……myDisplace(){P += N * mag;}…N = {RSLP = {RSL Compilermul $v1 N magadd PP $v1RRASMShader VMv1 = SIMD_Mul( N, mag );P= SIMD_Add(P, v1 );C24

Shading and SIMD (2)Vector SIMD_Add_FPU(Vector a, Vector b ){ for (i=0; i < vec_size; i += 1) {result[i] = a[i] + b[i]; } return result;}1xNo hardware SIMDSIMD_Add()Vector SIMD_Add_SSE(Vector a, Vector b ){ for (i=0; i < vec_size; i += 4) {SSE_Add( &result[i], &a[i], &b[i] ); } return result;}SSESIMD_Mul()4x…LRBniVector SIMD_Add_LRB(Vector a, Vector b ){ for (i=0; i < vec_size; i += 16) {LRB_Add( &result[i], &a[i], &b[i] ); } return result;}OpenCL, CUDA, ?16x25

Prospects for RibToolsWhat role will REYES play for real-time ?The architecture bodes well with multi-core, vector processors or even GPGPUDisplacement and curved surfaces are best with smaller-than-a-pixel polygons anywayDevelop, learn and innovateDon’t let the others decide for you..Fully programmable graphics hardware is comingOff-line rendering ?Much more complex, but no real-time constraintsDX11 tessellation..almost micro-polygons! *RenderAnts: REYES on GPGPUSiggraph 2008, 2009 **27* From Unigine’s Direct3D 11 tech demo ** Image from RenderAnts renderer

Cons and problemsRequires highly programmable hardware (best if with a flexible texture unit)The “RenderMan interface” is a fairly deep standard to followShader compilers, optimizers.. complex stuffComes with other issues:Cracks when tessellating, non-planar micropolys, front plane clipping, etc...but someone’s got to try it 8)28

Implementing a modern, RenderMan compliant, REYES renderer

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