Talk describes the challenge of combining rich VFX with interaction of animated characters. During the presentation will give an overview on setup of materials, scripting and programming. Profiling and background of technical constraints will also be brought up. This talk covers technical art topics, but artists and programmers will also find interesting details. Best for people familiar with Unreal Engine 4 or for those who want to see how to create current state of the art VFX with UE4.

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

2. Download Slides

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

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

5. Intro to wounds in games

6. 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

7. Fallout

8. Mortal Kombat

9. Dead Space

10. Shadow Warrior 2

11. Metal Gear Solid

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

13. Intro to wounds in games
Does your effect make sense? Need to follow character and game design!
vs vs

14. Intro to wounds in games
Alternatives?
Fixed presets
… why not combine both?

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

16. Intro to wounds in games
Popular methods:
• Ryan Brucks Unwraped Capture
• Tom Loomans PreSkinned Position
?
Dedicated system fitting:
• Creative and Art Director’s
Vision
• Game Requirements

17. Intro to wounds in games
Popular methods:
• Ryan Brucks Unwraped Capture
• Tom Loomans PreSkinned Position
?
Dedicated system fitting:
• Creative and Art Director’s
Vision
• Game Requirements
Case study: fighting with blades

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

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

20. Popular methods

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

22. Vlachos 2010, Rendering Wounds in Left 4 Dead 2, Valve
https://alex.vlachos.com/graphics/Vlachos-GDC10-Left4Dead2Wounds.pdf
Their problems
• Memory limits
• Performance Constraints
• Character variations
• LOD
• Avoid mesh generation

23. Vlachos 2010, Rendering Wounds in Left 4 Dead 2, Valve
https://youtu.be/5_G79LJ_l2Y

24. Vlachos 2010, Rendering Wounds in Left 4 Dead 2, Valve
https://www.youtube.com/watch?v=CHbnP5SAMzI

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

26. Popular Methods
• Ryan Brucks Unwraped Capture
• Tom Loomans Preskinned Position

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

28. Popular Methods
• Ryan Brucks Unwraped Capture
• Requires SceneCapture
• Each masked pixel need captured position
• Copy animation or use animated mesh
• Tom Loomans Preskinned Position

29. Popular Methods
• Ryan Brucks Unwraped Capture
• Requires SceneCapture
• Each masked pixel need captured position
• Copy animation or use animated mesh
• Tom Loomans Preskinned Position
• Hit calculation done in Rest Pose
• Hit need transformation into Rest Pose
ex. Bone Transform from Trace

30. Popular Methods
Ryan Brucks Unwraped Capture explained

31. Ryan Brucks Unwraped Capture explained

32. Ryan Brucks Unwraped Capture explained

33. Popular Methods
Ryan Brucks Unwraped Capture explained

34. Ryan Brucks Unwraped Capture explained

35. Ryan Brucks Unwraped Capture explained

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

37. Tom Loomans PreSkinned Position explained

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

39. Tom Loomans PreSkinned Position explained

40. Effect features and problems

41. 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

42. MaterialAttributes Functions, Blending with mask

43. Ryan Brucks Unwraped Capture, Require 2 RenderTargets per each Character

44. Effect Features and Problems
Fitting shape of obstacle
Signed Distance Fields (SDF)
What info gives us SDF?

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

46. Effect Features and Problems
Fitting shape of obstacle
http://iquilezles.org/www/articles/distfunctions/distfunctions.htm
float sdSphere ( vec3 p, float r ) {
return length(p)-r;
}

47. Effect Features and Problems
Fitting shape of obstacle
http://iquilezles.org/www/articles/distfunctions/distfunctions.htm
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;
}

48. Appear dotted on fast movement of obstacle

49. Effect Features and Problems
Appear dotted on fast movement of obstacle
Keep info from previous frame
Sphere + Sphere = Capsule
Capsule + Capsule = Quad
+
+
=
=

50. Effect Features and Problems
http://iquilezles.org/www/articles/distfunctions/distfunctions.htm
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) );
}

51. Effect Features and Problems
http://iquilezles.org/www/articles/distfunctions/distfunctions.htm

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

53. Effect Features and Problems
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.

54. Variable number of obstacles and draw calls

55. Effect Features and Problems
Impact of the hit
Brush like feeling vs Impact - what gives impact
Trigger stroke with Collision Trace

56. Trigger stroke with Collision Trace

57. Effect Features and Problems
Impact from random limb collisions
Animation notify with info about currently active limb for damage

58. Animation notify with info about currently active limb for damage

59. Effect Features and Problems
Multiple Characters at once
Mesh occlusion - Extents Size

60. Effect meet profiling and gameplay

61. 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

62. Blueprint for sequencer, easy to debug

63. Blueprint for sequencer, easy to debug

64. Effect meets profiling and gameplay
Stress Test Scene (i7, 16 GB RAM, GTX 970 1080p)

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

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

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

68. Effect meets profiling and gameplay
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),
SceneCapture 1.77 ms per Character
MaskRenderTarget 0.09 ms per obstacle
512 x 512 px (RGB8, 1 MB),
SceneCapture 1.02 ms per Character
MaskRenderTarget 0.025 ms per obstacle

69. Effect meets profiling and gameplay
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

70. Effect meets profiling and gameplay
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

71. Interface for gameplay, stuctures and components

72. Interface for gameplay, WorldToLocal Character transformation

73. Interface for gameplay, MaskRenderer execution

74. Effect meets profiling and gameplay
Alternatives:
• Global Shaders
• ShaderDemoPlugin by Temaran
• Pixel Shader Example
• Compute Shader Example
Fork it!

75. Effect meets profiling and gameplay
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!

76. Effect meets profiling and gameplay
ShaderDemoPlugin by Temaran

77. ShaderDemoPlugin by Temaran, Shader class declaration

78. ShaderDemoPlugin by Temaran, Uniform Structs declarations

79. ShaderDemoPlugin by Temaran, usage in code

80. ShaderDemoPlugin by Temaran, adding render command to RHI

81. Final comparison

82. Final Comparison
vs
RestPose stays in budget SceneCapture does not

83. Demo

84. Demo

85. Demo

86. 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

87. Questions?

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