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

28th Feburary 2011 AMD‘s Favorite Effects

Live Connection


CS RIGID BODY SIMULATION


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


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)


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)


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


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


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


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


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] ); } }}


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



MAKING IT LOOK PRETTY …


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


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


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



Color


Light


Emissive etc


DOF


End• Questions?

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

David Hoff, Abe Wiley, Dan Roeger


Documents

DX11 TECHNIQUES IN HK2207