Advanced DX11 Techniques for Real-Time Graphics and Physics in AMD GPUs

2. DX11 TECHNIQUES IN HK2207 Takahiro Harada AMD

3. 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 AMD‘s Favorite Effects

4. Live Connection AMD‘s Favorite Effects

5. CS Rigid Body Simulation AMD‘s Favorite Effects

6. 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 AMD‘s Favorite Effects

7. 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 AMD‘s Favorite Effects GPU Gems3, Real-time Rigid Body Simulation on GPUs

8. Mesh Collision (BVH) • 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 TriData AMD‘s Favorite Effects

9. Mesh Collision (BVH) • 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 AMD‘s Favorite Effects

10. 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 0 1 2 3 4 5 6 7 8 9 10 Body0 Body1 Body2 Body3 Body4 Body5 HitData AMD‘s Favorite Effects

11. Narrow Phase: 1 Thread Group 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] ); } } } } • 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 AMD‘s Favorite Effects

12. 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 AMD‘s Favorite Effects

13. 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 usage Better HW occupancy AMD‘s Favorite Effects

14. 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 Append Append Append Append Append Append AMD‘s Favorite Effects

15. Improved Narrow Phase 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] ); } } } } Void 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] ); } } } AMD‘s Favorite Effects

16. Result AMD‘s Favorite Effects

17. MAKING IT LOOK PRETTY … AMD‘s Favorite Effects

18. 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 AMD‘s Favorite Effects

19. 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 AMD‘s Favorite Effects

20. Other Techniques Used • Deferred shading • Depth of field • Emissive materials • Lens ghosting and flare • Aerial perspective • Reflections • Tone mapping • LUT color correction AMD‘s Favorite Effects

21. AMD‘s Favorite Effects

22. Color AMD‘s Favorite Effects

23. Light AMD‘s Favorite Effects

24. Emissive etc AMD‘s Favorite Effects

25. DOF AMD‘s Favorite Effects

26. End • Questions? • Acknowledgement • Jay McKee, Jason Yang, Justin Hensley, Lee Howes, Ali Saif, David Hoff, Abe Wiley, Dan Roeger AMD‘s Favorite Effects