The Technology behind

Jarosław PleskotSenior Engine Programmer

Flying Wild Hog

2014

Facts about Shadow Warrior

published by Devolver Digital 18 months production time team ~35 people (2 tech programmers, 6 total) modified Hard Reset’s engine (Roadhog)

Presentation overview

Act I, Skinned decals generation and rendering

Act II, Foliage authoring and rendering

Act III, Seawater rendering

Act I, Skinned decals

Skinned decals – entry point

In Hard Reset decals only on non-skinned geometry (static or movable) Characters destruction by showing/hiding parts of a model or by changing texture Lot of blood and gore in Shadow Warrior, must have skinned decals

Skinned decals – two techniques

1. Deffered decals [1][2]+ mesh generation not needed

+ small amount of data to store and pass to graphics card

- decal floats when mesh is animated

- can be projected on other surfaces, need to mask out (additional gbuffer usage or additional passes)

Source: http://broniac.blogspot.com/2011/06/deferred-decals.html

Skinned decals – two techniques

2. Geometry based [3]+ stable result when animating mesh

+ cover only desired surface

- mesh generation: time and memory

- additional input data required to generate a decal

Skinned decals – two techniques

2. Geometry based [3]+ stable result when animating mesh

+ cover only desired surface

- mesh generation: time and memory

- additional input data required to generate a decal

Skinned decals – input data

Load vertex buffer into CPU memory Generating adjacency per each triangle in mesh 3 adjacent triangles Mesh can consist of many isolated elements => adjacency groups (store first triangle index of each adjacency group)

struct STriangleAdjacency

{ UInt32 m_adj0; UInt32 m_adj1; UInt32 m_adj2; UInt32 m_group;};

Skinned decals – generation

Asynchronous (job based) Copy decal parameters and skinning matrices to job

Basic algorithm

for all adjacency groups{ find triangle closest to hit point expand decal by adding adjacent triangles until size reached

and calculate UVs and TBN for each new triangle}

Skinned decals – generation

1. Find triangle closest to hit point

Don't want to process entire mesh Skeleton and weights == skinned mesh is naturally divided In preprocess step create triangle list for every bone Iterate through selected and adjacent bones' lists Use skinning matrices to get worldspace positions

Skinned decals – generation

2. Expand decal

add hit triangle to “open” listwhile open list not empty{ pop front and calculate its vertices’ positions if any inside decal (bounding box test, sizeZ = max( sizeX,

sizeY )) { add triangle to the output list with new UVs and TBN add adjacent triangles to “open” list if not already

processed }}

Skinned decals – generation

2. Expand decal

add hit triangle to “open” listwhile open list not empty{ pop front and calculate its vertices’ positions if any inside decal (bounding box test, sizeZ = max( sizeX,

sizeY )) { add triangle to the output list with new UVs and TBN add adjacent triangles to “open” list if not already

processed }}

Special case for first triangle:

If triangle field > decal field always pass bounding box test

Skinned decals – dismemberment

Character dismemberment implemented Decals must be split, how?

Skinned decals – dismemberment

First version

Store decal spawn info, recompute on destruction

- additional CPU time

(5 enemies destroyed at once can produce 50 jobs)

- cannot show anything until recomputed decal arrive == blink

Skinned decals – dismemberment

Second version Character dismemberment is hand- made by creating separate meshes Modify spawn algorithm – create separate decal chunks for every visible mesh Input: adjacency per chunk On cutting create new decals that references initial decal geometry Render proper decal chunks

Skinned decals – dismemberment

Second version

+ no recomputation

+ split decals available instantly

- more draws for initial decal (merge on render)Modified algorithm

for all visible chunks{ for all adjacency groups { find triangle closest to hit point expand decal chunk by adding adjacent triangles until size

reached and calculate UVs and TBN for each new triangle

}}

Skinned decals – rendering

Rendered through dynamic vertex buffers One pass (compose) or 2 passes (normal+compose) Possible animation through alpha test level shifting (lower alpha test reference value == bigger decal)

Skinned decals – details

Decal size hard limit: 10k vertices Decal count limit: 100 decals (FIFO) Vertex memory: 30 MB total, in pool Typical bullet decal (500 triangles) spawn time

around 0.5 ms on Intel core i7 (async, still can do better) Big decals == skinned geometry rendered multiple times, avoid them, use other techniques, e.g. texture layering Use „clamp to border color” with alpha 0.0

Act II, Foliage system

Foliage system – entry point

• In Hard Reset vegetation only in one area of one DLC level

• In Shadow Warrior many open levels: forests, villages, towns, etc.

• Vegetation made as level geometry == no LoD, no instancing, hard to create and control (overdraw)

Foliage system – entry point

Requirements:● Instancing● Specific LoD system● Easy to plant (levels created in 3dsmax,

gameplay in game editor)

Foliage system – entry point

Requirements:● Instancing● Specific LoD system● Easy to plant (levels created in

3dsmax, gameplay in game editor)

Spawn meshes – meshes with relative

foliage density stored as vertex color

Foliage system – planting

Spawn meshes for level 2 in 3ds Max

Foliage system – planting

• Render spawn meshes in top-down view to an image (density, position.z and normal)

• In 50x50cm blocks generate random plant positions (ρ = ρmesh * ρblock, pos.z interpolated)

• Set random yaw

• Optionally align with normal vector

• Store packed matrix

All random values are static!

Foliage system – planting

Many levels of foliage possible by splitting spawn meshes to separate 3dsmax objects

Foliage system – editor

Foliage system – storage

Initially one quad tree per map, batch index and LoD level stored with transformation

Changed to multi resolution grids (2 levels: 4x4 and 64x64 meters, one grid per batch)

Foliage system – storage

Grid node contains min/max Z coord and object ranges for low and high density arrays

Transformation packed into 32 bytesstruct SObject{ Half4 m_plane0; // 8 Half4 m_plane1; // 16 Half4 m_plane2; // 24 Vec3Packed64 m_position;// 32};

Foliage system – storagetypedef UInt64 Vec3Packed64;

#define POSITION_PACKED_PACK_SCALE 200.0f#define POSITION_PACKED_UNPACK_SCALE ( 1.0f / POSITION_PACKED_PACK_SCALE )

// 21 bit max#define VEC3PACKED64_MASK 0x00000000001fffff#define VEC3PACKED64_SIGN_RECOVER_SHIFT 11

inline Vec3Packed64 Vec3Packed64Pack( const Vec3& vec, Float packScale ){ return ( ( UInt64( vec.X * packScale ) & VEC3PACKED64_MASK ) << 42 ) | ( ( UInt64( vec.Y * packScale ) & VEC3PACKED64_MASK ) << 21 ) | ( UInt64( vec.Z * packScale ) & VEC3PACKED64_MASK );}

21 bits per component

± 5,2km with 2 mm resolution

Foliage system – storageinline Vec3 Vec3Packed64Unpack( const Vec3Packed64 vecPacked, Float unpackScale ){ Vec3 result; { Int32 value = Int32( vecPacked & VEC3PACKED64_MASK ); value <<= VEC3PACKED64_SIGN_RECOVER_SHIFT; value >>= VEC3PACKED64_SIGN_RECOVER_SHIFT; result.Z = Float( value ) * unpackScale; } { Int32 value = Int32( ( vecPacked >> 21 ) & VEC3PACKED64_MASK ); value <<= VEC3PACKED64_SIGN_RECOVER_SHIFT; value >>= VEC3PACKED64_SIGN_RECOVER_SHIFT; result.Y = Float( value ) * unpackScale; }

{ Int32 value = Int32( ( vecPacked >> 42 ) & VEC3PACKED64_MASK ); value <<= VEC3PACKED64_SIGN_RECOVER_SHIFT; value >>= VEC3PACKED64_SIGN_RECOVER_SHIFT; result.X = Float( value ) * unpackScale; }

return result;}

Shift arithmetic

right!

Foliage system – rendering

• Dynamic vertex buffer, 8192 instances max

• Several batches (one batch == all visible objects with the same mesh and materials)

• LoD levels:Low – 20% density, range multiplier x1

High – 100% density, range multiplier x1

Ultra – 100% density, range multiplier x2

• Gather with Z range ±15 meters

• Dissolve out on last 5 meters

Foliage system – details

• Gather time for 8192 instances in 9 batches: 0.41 ms on Intel core i7 3.4 GHz

• GPU time: 1.22 ms (0.89 normal + 0.33 compose, 730k + 470k PSPixelsOut) on Radeon R9 270, 1920x1080

• Memory usage: from 0.7 to 10 MB per level

Foliage system – results

~4200 instances gathered

Foliage system – results

~6400 instances gathered

Foliage system – results

Not only plants. Our artists are very creative!

Act III, Seawater

Seawater – entry point

• Docks location with stormy weather planned in Shadow Warrior

• DX9 renderer (no hw tesselation)

• Dedicated translucent water shader used in Hard Reset (simple waves, refraction, water fog, foam)

Seawater – mesh

• 3 LoD levels (quad size: 0.5 x 0.5, 2x2, 8x8 meters, LoD 0 dims: 48x48 meters)

• Edge vertices stretched beyond camera far Z

• 33k tris total

• Mesh moved with camera, snapped to integer world coordinates (constant sampling positions)

• Stencil test

Seawater – vertex shader

Position processing

Distortion Filter Asymmetry Choppiness Add vertex texture

Flatten edges

Distortionderivative

Filter Flatten edges

Modulate

Normals

Distortionderivative

w. phase offset

Filter Bias and modulate

Foam multiplier

Affect and orthogonalize

TBN

Seawater – distortionfloat4 fWaterGeomWave0; // xy - frequency, z - speed, w – amplitude…

float DistortionFunc( float arg, float4 params ){

float modBase = 0.5 + sin( arg * params.x ) * 0.5;float modArg = modBase * params.y - params.y;float modAmp = modBase * params.z - params.z;return sin( arg * ( 1.0 + modArg ) ) * ( 1.0 + modAmp );

}

float DistortionDerivativeFunc( float arg, float4 params ){

float modBase = 0.5 + sin( arg * params.x ) * 0.5;float modArg = modBase * params.y - params.y;float modAmp = modBase * params.z - params.z;return cos( arg * ( 1.0 + modArg ) ) * ( 1.0 + modAmp );

}

#define DISTORTION_0( arg ) DistortionFunc( arg, fWaterGeomWave0FunctionParam )…#define D_DISTORTION_0( arg ) DistortionDerivativeFunc( arg, fWaterGeomWave0FunctionParam )…float arg0 = dot( posWS.xy, fWaterGeomWave0.xy ) + time * fWaterGeomWave0.z;…

Randomize waves

reusing wave parameters

(HACK)

Seawater – waves

• Sea waves are the signal, mesh is a sampling mechanism

• Nyquist theroem: sampling frequency must be at least 2 times higher than peak signal frequency to avoid aliasing

• Different LoD == different sampling frequencies

Seawater – waves

Solution:

• Calculate cuttoff frequency for each vertex

• Pass it to a shader as a vertex attribute

• Filter waves generated in vertex shader using this frequency limitstruct WaterVertex

{ Vec3 m_pos; Half2 m_uv0; Half2 m_uv1; Float m_geomSoftness; Float m_waveFreqLimit;};

Seawater – filter

Diagonal direction has lowest sampling frequency

Lerp cutoff frequencies on LoD boundaries

Only fc0 and fc1 used in practice

Seawater – filter

float DistortionFilter( vert_in i, float2 waveFreq ){

float waveFreqEff = length( waveFreq.xy );float val = -2.5 / i.m_waveFreqLimit * ( waveFreqEff -

i.m_waveFreqLimit * 0.8 );float filter = saturate( 0.5 + 0.5 * val );return filter;

}

Seawater – filter

float DistortionFilter( vert_in i, float2 waveFreq ){

float waveFreqEff = length( waveFreq.xy );float val = -2.5 / i.m_waveFreqLimit * ( waveFreqEff -

i.m_waveFreqLimit * 0.8 );float filter = saturate( 0.5 + 0.5 * val );return filter;

}

#define CALC_FILTER_0 float filter0 = DistortionFilter( i, fWaterGeomWave0.xy )#define CALC_FILTER_1 float filter1 = DistortionFilter( i, fWaterGeomWave1.xy )#define CALC_FILTER_2 float filter2 = DistortionFilter( i, fWaterGeomWave2.xy )#define CALC_FILTER_3 float filter3 = DistortionFilter( i, fWaterGeomWave3.xy )

#define FILTER_0( val ) filter0*val#define FILTER_1( val ) filter1*val#define FILTER_2( val ) filter2*val#define FILTER_3( val ) filter3*val

Seawater – wave asymmetry

float distort = 0.0;distort += FILTER_0( DISTORTION_0( arg0 ) * fWaterGeomWave0.w );…// FLATTENING STAGEposWS.z += distort * i.m_geomSoftness;

// NORMAL DISTORTION CODE NEEDED TO AFFECT POSITIONfloat cos0 = FILTER_0( D_DISTORTION_0( arg0 ) );float2 diff0 = i.m_geomSoftness * normalize( fWaterGeomWave0.xy ) * cos0 );…

// ASYMMETRY AND CHOPPINESS#define ASYMMETRY( arg, power ) ( arg > 0.0 ? power * arg*arg : 1.0 )

posWS.xy += diff0 * fWaterGeomWaveChoppiness.x *ASYMMETRY( cos0, fWaterGeomWaveAsymmetry.x );

Seawater – wave asymmetry

// ASYMMETRY AND CHOPPINESS#define ASYMMETRY( arg, power ) ( arg > 0.0 ? power * arg*arg : 1.0 )

posWS.xy += diff0 * fWaterGeomWaveChoppiness.x * ASYMMETRY( cos0, fWaterGeomWaveAsymmetry.x );

Seawater – vertex texture

• Displace vertices with perlin noise to avoid wave tiling

• Only LoD 1 and LoD 2

• Calculate proper mip level to avoid aliasing

• 256x256 R32F vertex texture

• 1024x1024 normals (read in PS)

Seawater – pixel shader

• Translucent at the begining, changed to opaque later on

• 2 x diffuse (water + foam)

• 2 sliding normals + perlin noise normal

• Environment map

• Deffered lighting

Seawater – results

• GPU time 0.80 ms (0.02 ms mask, 0.25 ms normal, 0.53 ms compose) @ Radeon R9 270, 1920x1080

• 0 pixels draw (depth & stencil fail): 0.16 ms (0.00 ms mask, 0.07 ms normal,

0.09 ms compose)

• 0 pixels draw (stencil fail): 0.39 ms (0.00 ms mask, 0.30 ms normal,

0.09 ms compose)

Special thanks

Łukasz Zdunowski – Lead Artist

Zbigniew Siatecki – Environment Artist

Dominik Misiurski – FX Artist

Artur Maksara – Producer

… and the rest of our team.

References

1. http://broniac.blogspot.com/2011/06/deferred-decals.html

2. http://humus.name/index.php?page=3D&ID=83

3. “Character Animation with Direct3D”, Carl Granberg, Charles River Media, 2009

Questions?Contact:Email: jarek.pleskot AT flyingwildhog.comFacebook: Jarosław PleskotTwitter: @JaroslawPleskot