Dynamic Wounds on Animated Characters in UE4

Dynamic Wounds on Animated Characters
in UE4
Michał Kłoś, Layopi Games
Game Industry Conference 2017

About me
Now Shader/VFX Artist Lead at Layopi Games
Lead Native Dev at VR Global
Unity & Web Dev at TK Games

Agenda
• Intro to wounds in games
• Popular methods
• Effect features and problems
• Effect meets profiling and gameplay
• Final comparison

Intro to wounds in games
Wounds and dismemberment:
• Mortal Kombat
• Metal Gear Solid
• Dead Space
• Fallout
• Shadow Warrior 2
• Shadow of Mordor
and many more …
https://www.youtube.com/watch?v=RIUYi9JuMKQ

Why game need wounds:
• Visual feedback to damage
• Minimize UI, Healthbars
• Give satisfaction from combat
• Juiciness: persistence

Does your effect make sense? Need to follow character and game design!
vs vs

Alternatives?
Fixed presets
… why not combine both?

Hellblade: Senua's Sacrifice
www.youtube.com/watch?v=5aAgBAO9Lwc

Popular methods:
• Ryan Brucks Unwraped Capture
• Tom Loomans PreSkinned Position
?
Dedicated system fitting:
• Creative and Art Director’s
Vision
• Game Requirements

Popular methods:
• Tom Loomans PreSkinned Position
?
Dedicated system fitting:
• Creative and Art Director’s
Vision
• Game Requirements
Case study: fighting with blades

Decal projection makes it slide on animated meshes, it is bad!

Material with masked damage even allows for animation of strokes, we want this!

Vlachos 2010, Rendering Wounds in Left 4 Dead 2, Valve
https://alex.vlachos.com/graphics/Vlachos-GDC10-Left4Dead2Wounds.pdf

https://alex.vlachos.com/graphics/Vlachos-GDC10-Left4Dead2Wounds.pdf
Their problems
• Memory limits
• Performance Constraints
• Character variations
• LOD
• Avoid mesh generation

https://youtu.be/5_G79LJ_l2Y

https://www.youtube.com/watch?v=CHbnP5SAMzI

Popular Methods
• Tom Loomans Preskinned Position

Popular Methods
Problems
• Calculate mask on surface of animated geometry
• Keep updatable mask between frames

Popular Methods
• Requires SceneCapture
• Each masked pixel need captured position
• Copy animation or use animated mesh

Popular Methods
• Requires SceneCapture
• Each masked pixel need captured position
• Copy animation or use animated mesh
• Hit calculation done in Rest Pose
• Hit need transformation into Rest Pose
ex. Bone Transform from Trace

Popular Methods
Ryan Brucks Unwraped Capture explained

Ryan Brucks Unwraped Capture explained

Unique UV, outtake on texture morph animation that happens when UVs are mirrored

Tom Loomans PreSkinned Position explained

Red: Animated Bone Transform, Green: RestPose Transform, Blue: Inverse Animartion + RestPose Transform

Effect Features and Problems
• Blending with character material
• Fitting shape of obstacle
• Dotted on fast movement of obstacle
• Variable number of obstacles and draw calls
• Impact of hit
• Hits from random limb collisions

MaterialAttributes Functions, Blending with mask

Ryan Brucks Unwraped Capture, Require 2 RenderTargets per each Character

Fitting shape of obstacle
Signed Distance Fields (SDF)
What info gives us SDF?

Signed Distance Fields (SDF), What info gives us SDF? https://www.shadertoy.com/view/ldK3zD

http://iquilezles.org/www/articles/distfunctions/distfunctions.htm
float sdSphere ( vec3 p, float r ) {
return length(p)-r;
}

float sdCapsule (vec3 p, vec3 a, vec3 b, float r) {
vec3 pa = p-a, ba = b-a;
float h = clamp(dot(pa,ba)/dot(ba,ba), 0.0, 1.0);
return length(pa-ba*h)-r;
}

Appear dotted on fast movement of obstacle

Appear dotted on fast movement of obstacle
Keep info from previous frame
Sphere + Sphere = Capsule
Capsule + Capsule = Quad
+
+
=
=

float dot2(in vec3 v) { return dot(v,v); }
float udQuad (vec3 p, vec3 a, vec3 b, vec3 c, vec3 d) {
vec3 ba = b-a; vec3 pa = p-a; vec3 cb = c-b; vec3 pb = p-b;
vec3 dc = d-c; vec3 pc = p-c; vec3 ad = a-d; vec3 pd = p-d;
vec3 nor = cross(ba, ad);
return sqrt((sign(dot(cross(ba,nor),pa))
+sign(dot(cross(cb,nor),pb))
+sign(dot(cross(dc,nor),pc))
+sign(dot(cross(ad,nor),pd)) < 3.0)
? min(min(min(dot2(
ba*clamp(dot(ba,pa)/dot2(ba),0.0,1.0)-pa),
dot2(cb*clamp(dot(cb,pb)/dot2(cb),0.0,1.0)-pb)),
dot2(dc*clamp(dot(dc,pc)/dot2(dc),0.0,1.0)-pc)),
dot2(ad*clamp(dot(ad,pd)/dot2(ad),0.0,1.0)-pd))
: dot(nor,pa)*dot(nor,pa)/dot2(nor) );
}

Splines?
Read bone animation trail from SkeletalMeshComponent?
Interpolate 2+ frames?
Did not tried
https://www.shadertoy.com/view/XdB3Ww

Variable number of obstacles and draw calls
Draw sum of all of them at once and count instructions
Editor do not support Material Parameters Arrays
but Global Shaders do.

Variable number of obstacles and draw calls

Impact of the hit
Brush like feeling vs Impact - what gives impact
Trigger stroke with Collision Trace

Trigger stroke with Collision Trace

Impact from random limb collisions
Animation notify with info about currently active limb for damage

Animation notify with info about currently active limb for damage

Multiple Characters at once
Mesh occlusion - Extents Size

Effect meet profiling and gameplay

Effect meets profiling and gameplay
Profiling and 1ms budget for VFX
UE profiling tools
SceneCapture vs RenderMaterialToTexture Performance
RenderTarget performance vs quality
WorldSpace vs LocalSpace

Blueprint for sequencer, easy to debug

Stress Test Scene (i7, 16 GB RAM, GTX 970 1080p)

Numbers per MaskRenderTarget resolution:
2048 x 2048 px (RGB8, 16 MB),
SceneCapture 5.22 ms per Character
MaskRenderTarget 0.35 ms per obstacle
1024 x 1024 px (RGB8, 4 MB),
512 x 512 px (RGB8, 1 MB),

Solution:
Transform Hit to Rest Pose instead of SceneCapture
Effect need texture mask done with DrawMaterialToRenderTarget
but it draws on quad with no info about Rest Pose
...so bake RestPose to texture at start and sample each time

Interface for gameplay
Enqueue calls each frame and restrict limit
Service with Logic - Component with State approach,
easy to plug to character
Feed with WorldSpace vs LocalSpace

Interface for gameplay, stuctures and components

Interface for gameplay, WorldToLocal Character transformation

Interface for gameplay, MaskRenderer execution

Alternatives:
• Global Shaders
• ShaderDemoPlugin by Temaran
• Pixel Shader Example
• Compute Shader Example
Fork it!

www.unrealengine.com/en-US/blog/how-to-add-global-shaders-to-ue4
// MyTest.usf
// Simple pass-through vertex shader
void MainVS( in float4 InPosition : ATTRIBUTE0, out float4 Output : SV_POSITION ) {
Output = InPosition;
}
// Simple solid color pixel shader
float4 MyColor; float4 MainPS() : SV_Target0 {
return MyColor;
}
Global Shaders, finally!

ShaderDemoPlugin by Temaran

ShaderDemoPlugin by Temaran, Shader class declaration

ShaderDemoPlugin by Temaran, Uniform Structs declarations

ShaderDemoPlugin by Temaran, usage in code

ShaderDemoPlugin by Temaran, adding render command to RHI

Final Comparison
vs
RestPose stays in budget SceneCapture does not

Takeaways
• Make sure your effects meet design of game and characters
• Effects give visual feedback to game events
• SceneCapture renders whole scene with lights and shadows
• SceneCapture may be performed only at start or even offline saved as asset
• Rest pose is best approach for calculations
• DrawMaterialToRenderTarget is rather cheap

Thank you
@_spolsh
github.com/sp0lsh
michal.m.klos@gmail.com

Dynamic Wounds on Animated Characters in UE4

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