tressfx the fast and the furry by nicolas thibieroz
TRANSCRIPT
TRESSFXTHE FAST AND THE FURRY
AMD AND MICROSOFT DEVELOPER DAY, JUNE 2014, STOCKHOLM
NICOLAS THIBIEROZWORLDWIDE GAMING ENGINEERING MANAGER, AMD
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM2
TRESSFX: NEXT-GENERATION HAIR AND FUR RENDERING
The time for next-gen quality is now Tomb Raider pioneered next-gen hair
‒ Includes PS4/XB1
Users expect this level of quality for next-gen titles You need to start thinking about this!
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM3
WHAT MAKES GOOD HAIR/FUR?
Basic Rendering Antialiasing Antialiasing + Self Shadowing
Antialiasing + Self Shadowing
+ Transparency
Demo
All three components are a must to ensure high quality Transparency in particular is essential to next-gen visuals
‒ Requires an Order-Independent Transparency (OIT) solution
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM4
ISOLINE TESSELLATION FOR HAIR/FUR? 1/2
Isoline tessellation has two tessellation factors‒ First is line density (lines per invocation)‒ Second is line detail (segments per line)
In theory provides easy LOD system‒ Variable line density and detail by increasing both tessellation factors based on distance
Tess = (1,1) Tess = (2,1) Tess = (2,2) Tess = (2,3) Tess = (3,3)
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM5
ISOLINE TESSELLATION FOR HAIR/FUR? 2/2
In practice isoline tessellation is not cost effective for this scenario Lines are always 1-pixel thick
‒ Need Geometry Shader to extrude them into triangles for smooth edges‒ Major impact on performance!
‒ Alternative is to enable MSAA‒ Most engines are deferred so this causes a large performance impact
‒ No extrusion for smoothing edges and no MSAA = poor quality!
Bottom line: a pure Vertex Shader solution is faster‒ Curvature is rarely a problem (dependant on vertices/strands at authoring time)‒ If needed LOD benefit can be done in Vertex Shader
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM6
TRESSFX RENDERING PIPELINE
TressFX 2 uses a deferred approach for best performance
Three main steps STEP 1: Hair simulation STEP 2: Store fragment properties into buffers STEP 3: Fetch fragment properties, sort, selective shading and render
‒ Full shading on K-frontmost fragments‒ “Tail” fragments are shaded with a simpler light equation and shadowing algorithm
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM7
TRESSFX RENDERING PIPELINESTEP 1: HAIR SIMULATION
CSCSCS
Input Geometry (SRV)
Post-simulation geometry (UAV)
Simulation parameters
Pre-simulation line segments (model space)
Post-simulation line segments (world space)
Simulation compute shadersEdge length constraintLocal shape constraintGlobal shape constraint Not always needed for furModel TransformCollision Shape Not always needed for furExternal Forces (wind, gravity, etc.)
Input model is a collection of line segments (each segment composed of up to 64 vertices) Optionally divided into “master strands” and “slave strands” to optimize simulation performance
‒ Only master strands are simulated (e.g. 1:4 ratio)‒ Slave strands use master strand simulation results with added noise‒ Virtually no difference from full-scale simulation but much better simulation performance!‒ Master:slave simulation ratio can also vary with distance for even better performance
Demo
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM8
TRESSFX RENDERING PIPELINESTEP 2: STORE FRAGMENT PROPERTIES INTO BUFFERS
VS
World space
Index Buffer
Indexed triangle list
10
1
2
3 2
4
0
5
Extrusion into triangles
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM9
LINE SEGMENT EXTRUSION INTO TRIANGLES
A lot of vertices go through rendering high-quality hair or fur!‒ Geometry processing can therefore be a significant bottleneck
In previous versions of TressFX extrusion was done in Geometry Shader (don’t do it!) and then VS with Draw() Much faster performance was obtained with pure VS solution and precomputed index buffers
‒ Maximizes post vertex cache use!
DrawIndexed() method
Indexed triangle list = { ( 0, 1, 2 ), (2, 1, 3 ), ( 2, 3, 4 ), (4, 3, 5 ), ( … ) };
Line segments Expanded quads
10
1
2
3 2
4
0
5
1,4
Draw() method
Line segments Expanded quads
0
1
2
3,562,3
7,10
8,9
0
11
Triangle list = { ( 0, 1, 2 ), ( 3, 4, 5 ), ( 6, 7, 8 ), (9, 10, 11 ), ( … ) };
SLOW!FAST!
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM10
TRESSFX RENDERING PIPELINESTEP 2: STORE FRAGMENT PROPERTIES INTO BUFFERS
Antialiasing
VS PS
Homogeneous clip space
World space
Index Buffer
Indexed triangle list
10
1
2
3 2
4
0
5
Extrusion into triangles
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM11
ANTIALIASING
Antialiasing (aka “coverage”) using analytical method‒ This is NOT Multisampling Anti-Aliasing!
Compute pixel coverage on edges of hair strand triangles and convert it to an alpha value
Alpha value fades out based on distance from pixel centre to strand axis Similar principle to Emil Persson’s phone wire Anti-Aliasing
http://www.humus.name/Articles/Persson_GraphicsGemsForGames.pdf
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM12
TRESSFX RENDERING PIPELINESTEP 2: STORE FRAGMENT PROPERTIES INTO BUFFERS
Antialiasing
depth
tangent
coverage
next
VS PS
Homogeneous clip space
World space
Null RT
Stencil
PPLL UAV
Head UAV
Index Buffer
Indexed triangle list
10
1
2
3 2
4
0
5
Extrusion into triangles
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM13
PER-PIXEL LINKED LISTS
Head UAV‒ Each pixel location has a “head pointer” to a linked list in the PPLL 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;
depth
tangent
coverage
next
PPLL UAV
Head UAV
Memory requirements can be large!‒ Width * Height * Average overdraw * sizeof (PPLL structure)‒ Can use tiling approach in memory-constrained situations
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM14
TRESSFX RENDERING PIPELINESTEP 3: FETCH FRAGMENTS, SORT, SELECTIVE SHADING AND RENDER
VS PS
Stencil
Head UAV
PPLL UAV
Lighting
Full Screen Quad/Triangle
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM15
LIGHTING
Different options available‒ Kajiya-Kay hair lighting model‒ Marshner model‒ Anything else that looks good!
Fragment properties storage requirements may limit your options!
TressFX 2 sample uses an approximation of the Marchner technique when rendering two highlights‒ Unique fragment properties: depth, tangent vector
Primary Highlights
Secondary Highlights
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM16
TRESSFX RENDERING PIPELINESTEP 3: FETCH FRAGMENTS, SORT, SELECTIVE SHADING AND RENDER
VS PS
Stencil
Head UAV
PPLL UAV
Lighting Shadows
Full Screen Quad/Triangle
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM17
SHADOWS
Three different cases
Hair self-shadowing‒ Essential component to give next-gen volumetric quality look‒ Simplified Deep Shadow Map technique
Hair casting shadows on body & environment‒ Body: Need a very soft look at close range (blur shadow map)‒ Environment: render (possibly simplified) hair geometry into cascaded shadow map
Environment casting shadows on hair‒ Sample environment shadow map at hair fragment rendering time
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM18
TRESSFX RENDERING PIPELINESTEP 3: FETCH FRAGMENTS, SORT, SELECTIVE SHADING AND RENDER
VS PS
Stencil
Head UAV
PPLL UAV K frontmost
fragment: full shading, sorting and manual blending
Lighting Shadows
Full Screen Quad/Triangle
Tail fragments: cheap shading, no sorting and manual blending
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM19
SELECTIVE FRAGMENT SHADINGTHIS IS WHERE THE MEAT OF THE CODE OCCURS!
// Go through the rest of the linked list, and keep closest k fragments but// not in sorted order[allow_uav_condition]for(int l=0; l < g_iMaxFragments; l++){ if(pointer == NULLPOINTER) break; int id = 0; float max_depth = 0;
// Find the furthest node in array [unroll]for(int i=0; i<KBUFFER_SIZE; i++) { float fDepth = kBuffer[i].depth; if(max_depth < fDepth) { max_depth = fDepth; id = i; } }
// get the start of the linked list from the head pointeruint pointer = LinkedListHeadSRV[In.vPosition.xy];
// Copy first K fragments from PPLL into KBuffer[]NODE Kbuffer[KBUFFER_SIZE];for(int p=0; p<KBUFFER_SIZE; p++){ if (pointer != NULLPOINTER) { kBuffer[p] = LinkedListSRV[pointer]; pointer = LinkedListSRV[pointer].uNext; }}
// If linked list node is nearer than the furthest one in the local array // exchange the node in the local array for the one in the linked list NODE Node = LinkedListSRV[pointer]; if (max_depth > Node.depth) { SWAP(Node, Kbuffer[i]); }
// Do simple shading and shadowing for nodes not part of the K closest fragments fragmentcolor = ComputeSimpleShading(Node); // Out of order blending fcolor.xyz = mad(-fcolor.xyz, fragmentColor.w, fcolor.xyz) + fragmentColor.xyz * fragmentColor.w; fcolor.w = mad(-fcolor.w, fragmentColor.w, fcolor.w);
// Retrieve next node pointer pointer = LinkedListSRV[pointer].uNext;}// Blend the k nearest layers of fragments from back to front, where k = KBUFFER_SIZEfor(int j=0; j<KBUFFER_SIZE; j++){ int id = 0; float max_depth = 0;
// Find the furthest node in the array for(int i=0; i<KBUFFER_SIZE; i++) { float fDepth = kBuffer[i].depth; if(max_depth < fDepth) { max_depth = fDepth; id = i; } } // Take this node out of the next search Node = KBuffer[id]; KBuffer[id] = (NODE)0;
// Do high quality shading and shadowing fragmentcolor = ComputeHighQualityshading(Node);
// Blend fragment color fcolor.xyz = mad(-fcolor.xyz, fragmentColor.w, fcolor.xyz) + fragmentColor.xyz * fragmentColor.w; fcolor.w = mad(-fcolor.w, fragmentColor.w, fcolor.w);}
return fcolor;
Fetch and store
first K fragments
into array
Fetch next fragment
and replace in array
if closer
Out of order cheap
shading and blending
for fragments outside
array
Sort, shade and
blend K frontmost
fragments in array
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM20
TRESSFX RENDERING PIPELINESTEP 3: FETCH FRAGMENTS, SORT, SELECTIVE SHADING AND RENDER
VS PS
Stencil
Head UAV
PPLL UAV
Render targetK frontmost fragment: full shading, sorting and manual blending
Lighting Shadows
Full Screen Quad/Triangle
Tail fragments: cheap shading, no sorting and manual blending
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM21
TRESSFX PERFORMANCEFAST AND FURRY
High number of fragments required for quality look Main bottleneck is shading all those fragments
‒ Not per-pixel linked list traversal!
Selective shading approach allows significant performance savings with minor or negligible quality tradeoffsTechnique Cost
Out of order, no shading 1.31 msOut of order, shading 2.80 msDeferred PPLL, selective shading 2.13 ms
Shading cost is ~ 1.5 ms
24% faster
Fur model with ~130,000 fur strandsRunning on AMD Radeon 7970 @ 1080p
Distance Sim LOD Disabled
Sim LOD Enabled
Close range 1.01 ms 1.01 msMedium range 1.01 ms 0.70 msLong range 1.01 ms 0.37 ms
Simulation LOD Distance-adaptive Shading and Simulation LOD further improves performance
“K frontmost fragments” value can inversely scale with distance
Distance Shading LOD Disabled
Shading LOD Enabled
Close range 3.26 ms 3.26 msMedium range
3.23 ms 1.77 ms
Long range 2.52 ms 0.64 ms
Shading LOD
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM22
CONCLUSION AND QUESTIONS?
Next-gen hair/fur look at real-time performance is possible now! Fast:
‒ Variable ratio master/slave compute simulations‒ Vertex Shader extrusion of segments into triangles (do not use tessellation + GS)‒ Deferred rendering with selective shading‒ Distance-based shading and simulation LOD‒ Optimized shaders!
Furry:
Full and free access to TressFX 2 SDK sample, code and documentation at:http://developer.amd.com/tools-and-sdks/graphics-development/amd-radeon-sdk/
| TRESSFX THE FAST AND THE FURRY | AMD AND MICROSOFT GAME DEVELOPER DAY - JUNE 2 2014, STOCKHOLM23
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