dx11 techniques in hk2207

DX11 TECHNIQUES IN HK2207

Takahiro HaradaAMD

HK2207• Demo for Radeon HD 6970• Based in Hong Kong 2207

Not just a single technique Cinematic with practical effects

– Physics effects Bullet CPU-physics

CS rigid body

– Procedural adaptive tessellation

– Lighting effects Deferred rendering

Post effects

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Live Connection

28th Feburary 2011 AMD‘s Favorite Effects

CS Rigid Body Simulation

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CS Rigid Body• For visual effect• Simulation using CS

– CS5.0 has full functionality to realize simulation

• Key Features of CS– Group shared memory

• Tree traversal• Narrowphase(NP)

– Atomics• Collision

– Random write

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Particle Representation• Approximate shapes with particles• Arbitrary convex mesh input

– Scan conversion

• Integration– A thread, rigid body

• Collision– A thread, particle

• Collision with mesh– Conversion to particles– Collide against triangles

GPU Gems3, Real-time Rigid Body Simulation on GPUs28th Feburary 2011 AMD‘s Favorite Effects

• BVH used for broad phase collision detection– Contains static scene triangles– Node : 4 children, 4 volumes– Pack a few triangles in a leaf

• Traversal efficiency• Separate data to another buffer

Mesh Collision (BVH)

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TriData

• Tree traversal– Traversal stack located in Thread Group Shared

Memory(TGSM)

• Traversal and Narrow phase(NP) are separated to keep high efficiency on the GPU– Less divergence– Reduce local resource usage

Mesh Collision (BVH)

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Narrow Phase• Output from tree collision

– HitData, List of triangle indices per body– Sparse

• 1 body x 1 leaf collision == n particles x m tris– Cache relevant triangles in TGSM

• Reduce memory traffic

– Use 1 thread group(TG) for a body 00 11 22 33 44 55 66 77 88 99 1010

Body0 Body1 Body2 Body3 Body5

HitData

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Body4

Narrow Phase: 1 Thread Group• 1 thread : 1 particle• Use 1 thread as a controller of the SIMD

– Read HitData -> LeafData– Share LeafData (TGSM)– All the threads are used to read 64 tris in parallel

• 64 collisions in parallel– AABB overlap test– 1 Triangle vs 64 particles collision

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Void NP(){ Bring64ParticlesIntoGPRs(); if( LOCAL_IDX == 0 ) LoadAllCollisionInfo(); BARRIER; forAllLeaves(;;) { forAllTriangles(;;j+=TG_SIZE) { fillTriangle( ldsVtx, ldsAabb , LOCAL_IDX ); BARRIER; for(k<TG_SIZE;k++) { if( ovelaps(ldsAabb[k]) ) collide( pData, ldsVtx[k] ); } } }}

Inefficiencies• Hit data buffer is sparse

– We launch too many TGs– TG with 0 hit returns after mem access

• Controller sections– Only controller is working– 63 threads are idle

• Redundant overlap test(Particle-Tri)– Body-Tri test is enough

• Leaf is not completely filled– Several leaves are colliding– Can issue more memory requests

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Introduce Prepass• Hit data buffer is sparse

– We launch too many TGs– TG with 0 hit returns after mem access

• Controller sections– Only controller is working– 63 threads are idle

• Redundant overlap test(Particle-Tri)– Body-Tri test is enough

• Leaf is not completely filled– Several leaves are colliding– Can issue more memory requests

• Use Append Buffer– A body/thread

• Use 64 threads to read– Less single thread work

• Do Body-Tri test

• Pack triangle Data– LeafA(4), LeafB(4) -> 8

Reduce local resource usageBetter HW occupancy28th Feburary 2011 AMD‘s Favorite Effects

Pre Narrow Phase• Use 1 thread for a body

– Read HitData -> LeafData -> Triangle

• Body-Triangle AABB test– 64 Particle-Triangle collisions– Store colliding triangle indices

• If any collide– Write to append buffer

• Write triangle index to contiguous mem

• Sorting by n hits improves divergence– Local sort

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AppendAppend AppendAppend AppendAppend AppendAppend AppendAppend AppendAppend

Improved Narrow PhaseVoid NP(){ Bring64ParticlesIntoGPRs(); if( LOCAL_IDX == 0 ) LoadNumHits();

BARRIER;

for(i<ldsHitTriData.m_n;i+WG_SIZE) { fillTriangle( ldsVtx[LOCAL_IDX] , i+LOCAL_IDX );

BARRIER;

for(j<WG_SIZE;j++) { collide( pData, ldsVtx[j] ); } }}

28th Feburary 2011 AMD‘s Favorite Effects

Void NP(){ Bring64ParticlesIntoGPRs(); if( LOCAL_IDX == 0 ) LoadAllCollisionInfo(); BARRIER; forAllLeaves(;;) { forAllTriangles(;;j+=TG_SIZE) { fillTriangle( ldsVtx, ldsAabb , LOCAL_IDX ); BARRIER; for(k<TG_SIZE;k++) { if( ovelaps(ldsAabb[k]) ) collide( pData, ldsVtx[k] ); } } }}

Result

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MAKING IT LOOK PRETTY …

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Procedural Adaptive Tessellation• Add surface detail using DX11 tessellation• Hull shader

– Calc tessellation factor using depth• Tessellator• Domain shader

– Interpolate vertex position, normal– Displacement factor using 3D Perlin noise

• Evaluate in local space– Displacement vector– Displace

• Pixel shader– Normal is gradient

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Cracks• Different tessellation factor on edge

– Objects are small enough– Sample depth at the center

• Discontinuous displacement vector– Normal is not continuous– Use convexity of geometry– Interpolate normal and vector from center

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Other Techniques Used• Deferred shading• Depth of field• Emissive materials• Lens ghosting and flare• Aerial perspective• Reflections• Tone mapping• LUT color correction

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28th Feburary 2011 AMD‘s Favorite Effects

Color

28th Feburary 2011 AMD‘s Favorite Effects

Light

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Emissive etc

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DOF

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End• Questions?

• Acknowledgement– Jay McKee, Jason Yang, Justin Hensley, Lee Howes, Ali Saif,

David Hoff, Abe Wiley, Dan Roeger

28th Feburary 2011 AMD‘s Favorite Effects