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![TressFX 1.0 RENDERING
PER-PIXEL LINKED LIST
GPU implementation of order independent transparency (OIT)
Head UAV
‒ Each pixel location has a “head pointer” to a linked list in the PPLL
UAV
Head UAV
PPLL UAV
‒ As new fragments are rendered, they are added to the next open
location in the PPLL (using UAV counter)
‒ A link is created to the fragment pointed to by the head pointer
‒ Head pointer then points to the new fragment
// Retrieve current pixel count and increase counter
uint uPixelCount = LinkedListUAV.IncrementCounter();
uint uOldStartOffset;
// Exchange indices in LinkedListHead texture corresponding to pixel location
InterlockedExchange(LinkedListHeadUAV[address], uPixelCount, uOldStartOffset);
// Append new element at the end of the Fragment and Link Buffer
Element.uNext = uOldStartOffset;
LinkedListUAV[uPixelCount] = Element;
13 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
PPLL UAV](https://image.slidesharecdn.com/gs-4147billbilodeau-131121143604-phpapp01/75/GS-4147-TressFX-2-0-by-Bill-Bilodeau-13-2048.jpg)
Uploaded byAMD Developer Central
GS-4147, TressFX 2.0, by Bill-Bilodeau
This document summarizes improvements to the TressFX hair rendering and simulation technology. TressFX 2.0 features improved performance through deferred lighting and shadowing, continuous LOD, and code restructuring. Rendering is faster through optimizations to the anti-aliasing, self-shadowing, and transparency techniques. The simulation is formulated with general constraints and solved using a tridiagonal matrix approach for better stability under various hair conditions like wet, dry, or with wind. Overall, TressFX 2.0 provides over 2x performance increases for hair rendering compared to the previous version.
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GS-4147, TressFX 2.0, by Bill-Bilodeau
- 1. TressFX 2.0 ANDBEYOND BILL BILODEAU, AMD DONGSOO HAN, AMD
- 2. TressFX 2.0 ANDBEYOND AGENDA TressFX Overview TressFX Rendering ‒ TressFX 2.0 improvements TressFX Physics Future Work 2 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
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- 4. TressFX OVERVIEW WHAT ISTressFX? Realistic hair rendering and simulation ‒ Used in Tomb Raider Goes beyond simple shells and fins representation used in games Hair is rendered as thousands of strands with self shadowing, antialiasing and transparency Physical simulation for each strand using GPU compute shaders Very flexible to allow for different hair styles and different conditions 4 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 5. TressFX RENDERING WHAT MAKESIT LOOK GOOD What goes into good hair? ‒ Anti-aliasing ‒ Volumetric self shadowing ‒ Transparency Basic Rendering Antialiasing Antialiasing + Self Shadowing 5 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT Antialiasing + Self Shadowing + Transparency
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- 7. TressFX RENDERING LIGHTING MODEL SecondaryHighlights Kajiya-Kay Hair Lighting Model ‒ Anisotropic hair strand lighting model ‒ Uses the tangent along the strand instead of the normal for light reflections ‒ Instead of cos(N, H) , use sin(T,H) Marschner Model ‒ Two specular highlights ‒ Primary light colored highlight shifted towards the tip ‒ Secondary hair colored highlight shifted towards the root ‒ TressFX uses an approximation of the Marchner technique when rendering two highlights 7 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT Primary Highlights
- 8. TressFX RENDERING ANTI-ALIASING Everyhair strand is anti-aliased manually ‒ Not using Hardware MSAA! Compute pixel coverage on edges of hair strands and convert it to an alpha value 8 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 9. TressFX RENDERING SELF SHADOWING Self Shadowing ‒ Uses a simplified Deep Shadow Map technique No Self Shadows 9 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT With Self Shadows
- 10. TressFX RENDERING TRANSPARENCY OrderIndependent Transparency (OIT) using a Per-Pixel Linked Lists (PPLL) Fragments are stored in link lists on the GPU Nearest K fragments are rendered in back to front order No Transparency 10 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT With Transparency
- 11. TressFX 1.0 RENDERING Howrendering was done in version 1.0 TressFX 1.0 Rendering ‒ Render hair strand geometry into A-buffer ‒ Do lighting, shadowing, and antialiasing ‒ Store fragment color with depth and coverage in per-pixel linked list (PPLL) ‒ Render the K nearest fragments (K-buffer) in back to front order ‒ Blend nearest K fragments in the correct order with transparency ‒ Blend the remaining fragments without sorting 11 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 12. TressFX 1.0 RENDERING A-BUFFERPASS Coverage Hair Geometry Vertex Shader Head UAV Pixel Shader Lighting PPLL UAV Shadows depth color coverage 12 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT next
- 13. TressFX 1.0 RENDERING PER-PIXELLINKED LIST GPU implementation of order independent transparency (OIT) Head UAV ‒ Each pixel location has a “head pointer” to a linked list in the PPLL UAV Head UAV PPLL UAV ‒ As new fragments are rendered, they are added to the next open location in the PPLL (using UAV counter) ‒ A link is created to the fragment pointed to by the head pointer ‒ Head pointer then points to the new fragment // Retrieve current pixel count and increase counter uint uPixelCount = LinkedListUAV.IncrementCounter(); uint uOldStartOffset; // Exchange indices in LinkedListHead texture corresponding to pixel location InterlockedExchange(LinkedListHeadUAV[address], uPixelCount, uOldStartOffset); // Append new element at the end of the Fragment and Link Buffer Element.uNext = uOldStartOffset; LinkedListUAV[uPixelCount] = Element; 13 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT PPLL UAV
- 14. TressFX 1.0 RENDERING K-BUFFERPASS K-Buffer Full Screen Quad Vertex Shader 14 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT Pixel Shader depth depth color depth color depth coverage color coverage color coverage coverage Transparency
- 15. TressFX 1.0 RENDERING HOWCAN WE MAKE IT FASTER? Observation ‒ All fragments are lit and shadowed equally ‒ Even the ones buried under dozens of hair fragments that you can’t see Solution ‒ Defer the lighting and shadowing until the k-buffer pass ‒ Render the nearest K fragments with high quality ‒ Render the remaining fragments with lower quality (but faster) 15 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 16. TressFX 2.0 RENDERING A-BUFFERPASS Hair Geometry Vertex Shader Pixel Shader Coverage depth coverage tangent next 16 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 17. TressFX 2.0 RENDERING K-BUFFERPASS K-Buffer Full Screen Quad Vertex Shader Pixel Shader Lighting 17 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT depth depth coveragedepth coverage depth tangent coverage tangentcoverage tangent tangent Shadows Transparency
- 18. TressFX 2.0 IMPROVEMENTS CONTINUOUSLODs Distance to camera can be used for reducing the density of the hair ‒ Uniformly remove hair strands from the rendering ‒ To compensate for missing strands, thicken the hair ‒ Adjust the minimum pixel coverage with distance Full Density Hair 18 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT Reduced Density Hair Reduced Density with Thicker Strands
- 19. TressFX 2.0 IMPROVEMENTS CODERESTRUCTURING TressFX11 Sample Code is much more modular All of the necessary TressFX code in separate files for ‒ Rendering ‒ Simulation ‒ Mesh management ‒ Asset loading Code for head rendering and sample framework are completely separate Main TressFXSimulate TressFXSimulate TressFXRender SceneRender SceneRender TressFXRender TressFXMesh Gaussian Filter ‒ Take the “TressFX” files to get just what you need Better variable names Removal of dead code 19 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT DX11Mesh TressFXAssetLoader TressFX Code ObjImport
- 20. TressFX 2.0 IMPROVEMENTS MISCELLANEOUSIMPROVEMENTS Vertex shader optimizations for rendering ‒ Draw call for hair now uses an index buffer with a triangle list instead of looking up indices from a buffer PPLL head buffer uses a RWTexture2D for better caching (tiled) Hair shadow on model is softer and less blocky Various shader code optimizations Porting Guide Download the new TressFX 2.0 sample soon from our Radeon SDK : http://developer.amd.com 20 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 21. TressFX 2.0 RENDERING MEMORYCONSIDERATIONS A-Buffer ‒ 2 UAVs ‒ Size determined by resolution ‒ Head of the Linked List UAV 250.00 200.00 ‒ Screen resolution RWTexture2D, DXGI_FORMAT_R32_UINT ‒ Per-Pixel Linked List UAV ‒ Structured Buffer, size = (number of pixels) x (avg hair layers) x (sizeof(LinkedListStructure)) ‒ Default average number of hair layers is 8 ‒ Linked list structure is currently 3 DWORDs: depth, coverage, tangent Limited memory, but unbounded linked list ‒ This means too many fragments for a given pixel can overflow the PPLL ‒ Can cause artifacts ‒ Typically this only happens if the camera gets too close 21 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT 150.00 720p 100.00 1080p 50.00 0.00 Total A-Buffer Memory (MB) Linked List Head Per-Pixel Linked List
- 22. TressFX 2.0 RENDERING PERFORMANCERESULTS 3 2.5 2.5 2 2 1.5 TressFX 1.0 1 TressFX 2.0 1.5 TressFX 1.0 TressFX 2.0 1 0.5 0.5 0 0 Total Hair Render Time (ms) A-Buffer Pass Total Hair Render Time (ms) K-Buffer Pass R9 280x R9 290x > 2X performance increase! 22 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT A-Buffer Pass K-Buffer Pass
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- 24. TressFX Simulation Topics TressFX1.0 Simulation Overview ‒ Main Interest ‒ Simulation Overview ‒ Constraints ‒ Global shape constraints ‒ Local Shape Constraints ‒ Edge length constraints ‒ Problems TressFX Beyond ‒ General Constraint Formulation ‒ Tridiagonal Matrix-free Formulation ‒ Solving Linear System ‒ Benefits 24 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 25. Main Interest Maininterest of TressFX simulation ‒ Performance, performance and performance! – DirectCompute ‒ Styled hair – bending and twisting forces are important ‒ Stability – position based dynamics - Conditions – wet, dry or heavy - Wind – helps express dynamics even the character in the idle mode 25 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 26. Simulation Overview load hairdata precompute rest-state values – can be offline CPU while simulation running do apply gravity integrate apply GSC (Global Shape Constraints) GPU – DirectCompute apply LSC (Local Shape Constraints) apply wind apply ELC (Edge Length Constraints) collision handling vertex buffer 26 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT GPU – Rendering pipeline
- 27. GLOBAL SHAPE CONSTRAINTS GSC(Global Shape Constraints) ‒ The initial positions of particles serve as the global goal positions ‒ The goal positions are rigid w.r.t character head transform. ‒ You can think the initial positions are some cage and vertices are trapped in that cage during simulation. ‒ Easy and cheap. Help maintain the global shape but lose the detailed simulation initial goal position current position final position 27 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 28. LOCAL SHAPE CONSTRAINTS LSC(Local Shape Constraints) ‒ The goal positions are determined in the local frames. ‒ Still the goal positions are transformed in world frames and applied to vertex positions. initial goal position current position final position 28 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 29. LOCAL SHAPE CONSTRAINTS– CONT’ Local Transforms ‒ As in robotic arm, an open-chain structure has joints and each joint has parent-child relationships to its connected joints. ‒ 𝑖−1 𝑇𝑖 is to transform (translate and rotate) child space(i) to its parent space(i-1) ‒ With local transforms in chain structure, we can get a global transforms. 𝑤 𝑇𝑖 = 𝑤 𝑇0 ∙ 0 𝑇1 … ∙ 𝑖−2 𝑇𝑖−1 ∙ ‒ Local frames should be updated at each particles 29 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT 𝑖−1 𝑇𝑖
- 30. LOCAL SHAPE CONSTRAINTS– CONT’ Initialize and update local and global transforms ‒ Initialization is performed in CPU or offline only once. ‒ Update is performed at each frame in GPU. ‒ Update is serial process but independent to other strands. We update multiple strands in massive parallel processes in GPU. ‒ With local and global transforms, we can calculate target vertex positions for local shape constraints. ‒ Finally, update two neighboring vertices to get stable convergence. Updating position i Computing on local transform i-1 Zero 30 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 31. EDGE LENGTH CONSTRAINTS howmuch stretched or compressed 0.5 31 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT unit edge vector
- 32. Problems Extreme acceleration ‒When character makes a sudden move, it can generate extreme linear and angular acceleration which stretch hair very long. ‒ Even with high iterations with Edge Length Constraints, hair doesn’t recover the original length and as a result, hair can look too stretchy. ‒ Possible solution was to enforce Edge Length Constraints in the serial fashion from the root to the end of hair with extra damping – used for Tomb Raider ‒ We need a better way! And we did research! 32 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 33. Problems EXTREME ACCELERATION 33 TressFX2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
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- 35. General Constraint Formulation 35TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 36. Tridiagonal Matrix Formulation Special Formulation for Chain Structure such as Hair ‒ We don’t want to solve a big matrix equation, especially in GPU! ‒ Let’s take advantage of linear topology and serial indexing General case. We don’t want this! Known. Easy to compute them. Special case. Much simpler! Unknown and what we are solving for 36 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 37. SOLVING LINEAR SYSTEM Solving Linear System ‒ The formulation doesn’t require explicit matrix – Good for GPU! ‒ Diagonal, super and sub diagonal elements are non-zero - Sparse! ‒ The equation is diagonally dominant – Good for choice of direct solver! ‒ We can use tridiagonal matrix algorithm (Thomas algorithm) ‒ So we can solve it in GPU! 37 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 38. FUR CASTLE 38 TressFX2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 39. FUR MUSHROOM 39 TressFX2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 40. GRASS 40 TressFX 2.0and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 41. BENEFITS No moreiterations for Edge Length Constraints ‒ Needn’t have to guess number of iterations ‒ Fixed computation cost ‒ Fast convergence 41 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 42. TressFX 2.0 CONCLUSIONS TressFX2.0 performance now makes hair rendering faster than the previous version ‒ More than 2X faster in some cases TressFX is now fast enough to use on consoles More modular code structure means easier porting to your game Realistic physics for hair simulation can now be extended to other objects Stay tuned for more! ‒ Ongoing research to improve and expand the use of this technology 42 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 43. REFERENCE Real-time HairSimulation with Efficient Hair Style Preservation – Han, et al. VRIPHYS 2012 Tridiagonal Matrix Formulation for Inextensible Hair Strand Simulation – Han, et al. VRIPHYS 2013 43 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT
- 44. DISCLAIMER & ATTRIBUTION Theinformation presented in this document is for informational purposes only and may contain technical inaccuracies, omissions and typographical errors. The information contained herein is subject to change and may be rendered inaccurate for many reasons, including but not limited to product and roadmap changes, component and motherboard version changes, new model and/or product releases, product differences between differing manufacturers, software changes, BIOS flashes, firmware upgrades, or the like. AMD assumes no obligation to update or otherwise correct or revise this information. However, AMD reserves the right to revise this information and to make changes from time to time to the content hereof without obligation of AMD to notify any person of such revisions or changes. AMD MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE CONTENTS HEREOF AND ASSUMES NO RESPONSIBILITY FOR ANY INACCURACIES, ERRORS OR OMISSIONS THAT MAY APPEAR IN THIS INFORMATION. AMD SPECIFICALLY DISCLAIMS ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. IN NO EVENT WILL AMD BE LIABLE TO ANY PERSON FOR ANY DIRECT, INDIRECT, SPECIAL OR OTHER CONSEQUENTIAL DAMAGES ARISING FROM THE USE OF ANY INFORMATION CONTAINED HEREIN, EVEN IF AMD IS EXPRESSLY ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. ATTRIBUTION © 2013 Advanced Micro Devices, Inc. All rights reserved. AMD, the AMD Arrow logo and combinations thereof are trademarks of Advanced Micro Devices, Inc. in the United States and/or other jurisdictions. SPEC is a registered trademark of the Standard Performance Evaluation Corporation (SPEC). Other names are for informational purposes only and may be trademarks of their respective owners. 44 TressFX 2.0 and Beyond NOVEMBER 12, 2013 | AMD DEVELOPER SUMMIT