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EVGENY MAKAROV , DEVTECH NVIDIA
NVIDIA TURF EFFECTS: MASSIVE GRASS RENDERING WITH DYNAMIC SIMULATION - - PowerPoint PPT Presentation
NVIDIA TURF EFFECTS: MASSIVE GRASS RENDERING WITH DYNAMIC SIMULATION - - PowerPoint PPT Presentation
NVIDIA TURF EFFECTS: MASSIVE GRASS RENDERING WITH DYNAMIC SIMULATION EVGENY MAKAROV , DEVTECH NVIDIA OUTLINE Real-time grass rendering Turf Effects: grass rendering Turf Effects: dynamic simulation Grass authoring Q&A REAL-TIME GRASS
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REAL-TIME GRASS RENDERING
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PARTICLE BASED GRASS
Billboards Grass objects
Top view
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PARTICLE BASED GRASS
Pros
Good density Plausible rendering results Good performance
Cons
View dependent Complicated physical interaction
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GEOMETRY BASED GRASS
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GEOMETRY BASED GRASS
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GEOMETRY BASED GRASS
Pros
High density Looks good at any scale Simplified physical interaction Two-sided lighting and self-shadowing
Cons
High rendering complexity
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TURF EFFECTS: GEOMETRY BASED GRASS
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BREAK GRASS INTO A SET OF PATCHES
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RENDERING A GRASS BLADE +
Vertex shader Hull shader Domain shader u v (u1,v1)
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PATCH INITIALIZATION
Application provides a set of seed points Seed point
Position Expansion Asset ID u v 1
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SEED PARAMETERS
Bunching (radial alignment) Dispersal (coverage radius) LOW HIGH
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GRASS PATCH RENDERING
Build a list of visible patches Library renders data for a single asset type at once Render PatchesNum * AssetsNum Need to minimize API state changes
Use single API call per patch per asset for (n = 0; n < patchPerAssetCount; n++)
DrawInstanced(…, patchID);
~18.0 millions DrawInstanced() calls/sec*
* i7 4770K 3.5GHz, GeForce GTX 960 driver 347.52
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OCCLUSION CULLING
Per patch occlusion culling on GPU Use application provided depth with occluders information Rasterize per patch conservative boundary boxes with read-only depth
k j i OCCLUDER k i
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OCCLUSION CULLING
void DrawInstanced( UINT VertexCountPerInstance, UINT InstanceCount, UINT StartVertexLocation, UINT StartInstanceLocation );
… …
k
… …
i
. . .
k+1 k-1
. . . … k i . . . 1 1
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RENDERING WITH OCCLUSION CULLING
Per asset:
Write per patch blade count Call DrawInstancedIndirect() to render each patch
Culled patches would still issue draw calls on CPU
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VARYING DENSITY
Reduce blade count for distant patches Analytically defined Use fixed number of discrete LODs with smooth transitions
1 distance density level 0 level 1 level 2 d
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VARYING DENSITY
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VARYING DENSITY
Close up patch view Distant patch view (<10% of original blades)
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DYNAMIC SIMULATION
Grass interacts with dynamic scene objects
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DYNAMIC SIMULATION (2)
Simulate collision with per-blade control points Use mass-spring model
F2 F1 m1 m2
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EXTERNAL FORCES
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EXTERNAL FORCES
RENDER VOLUME
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EXTERNAL FORCES
RENDER VOLUME
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EXTERNAL FORCES
F = kΔ Δ v Fcombined
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DYNAMIC SIMULATION
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SIMUALTION SUMMARY
Encode dynamic objects in a form of deformation heightfield
Patch-space distance to occluder Per-pixel movement speed
Landscape is also a heightfield Per asset simulation parameters
Stiffness Restitution
Do not resolve collisions between individual grass blades
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GRASS AUTHORING
Seed parameters
Control blades distribution
Asset parameters
Control individual blade look
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ASSET PARAMETERS
Width
float4(w0, w1, w2, w3)
Tip Root w3 w2 w1 w0 (1,1,1,1) (1,1,1,0) (0,1,1,1)
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VARYING SMOOTHNESS
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ASSET PARAMETERS (2)
Edge offset Density falloff Shape variations
A set of “barebones” used for particular grass type
2 user-defined CPs 3 user-defined CPs
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SUMMARY
Turf Effects: real-time grass simulation and rendering Currently uses tessellation (D3D 11.0 or OpenGL 4.0) Can rely on existing content
Convert existing particle-based grass into geometry
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Q&A
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