Custom fabric shader for unreal engine 4
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This document discusses a custom fabric shader developed for Unreal Engine 4 by Gregory Dongseok Kim, detailing various types of fabrics, their properties, and limitations of existing shader models. The approach incorporates Oren-Nayar diffuse shading and a unique specular model to accurately represent materials from non-metallic fabrics like cotton to metallic styles such as silk. The aim is to provide an easy-to-use shader for artists, allowing for realistic rendering of fabric characteristics in digital environments.
Custom fabric shader for unreal engine 4
- 1. Custom Fabric Shader for Unreal Engine 4 Gregory Dongseok Kim 2016-04-11
- 2. ￭ Two types of Fabric ⚬ Non-Metal: Cotton, denim, flax and common fabrics ⚬ Metal: Silk, satin, velvet, nylon and polyester ￭ The Order approach ￭ Limitations of Unreal Engine shader ￭ My approach ⚬ Oren-nayar diffuse shading ⚬ Specular Term ⚬ Fiber Scatter Term ￭ Result Overview 2
- 3. Two types of Fabric: Non-Metal ￭ Cotton, Denim, Flax and Common fabrics ⚬ Tiny furs on each fibers ⬝ Roughness value of those fabrics is always 1.0 unless they wet ⬝ Reflect lights to random directions ⬝ It induces not only front scattering but also back scattering Fuzz on rim part ⚬ Specular lobe is widely spread on view direction surface ⬝ Specular color is white but it is looked like desaturated color of base one because of front scattering 3
- 4. Two types of Fabric: Metal (1) ￭ Silk, Satin, Velvet, Nylon and Polyester ⚬ Silk has round triangular cross section and smooth surface ⬝ It induces simiral reflection with metal ⬝ Smooth surface: Reflects lights as perfect as metal surface ⬝ Triangular cross section: Reflects specific light wave ⚬ Silk can have Roughness value around 0.3 - 0.7 ⬝ Thickness of each fibers is 5 - 10 μm ⬝ Thin to make smooth surface as metal 4
- 5. Two types of Fabric: Metal (2) ￭ Special properties of Silk and Satin ⚬ They have much less fuzz on rim part then cotton or common fabrics ⬝ Their intensive structure makes similar specluar with metal’s one ⚬ They can have various specular colors ⬝ If they are woven by different colors strings ⬝ Specular color can be changed by view direction ⚬ They have anistropic specular shape 5
- 6. Two types of Fabric: Metal (3) ￭ Special properties of Velvet ⚬ Tiny fibers are attached on the surface ⬝ Its Roughness value has to be 1.0 ⬝ If the light is behind, those fibers give foward scattering and it gives rim light effect on edge part ⚬ Diffuse shading is simiral with metal’s diffusion ⬝ Its surface color is darker than original color of fibers 6
- 7. The Order approach1 ￭ Custom microfiber model ⚬ Ashikhmin’s Distribution based BRDF for fresnel term ⚬ Inverse Gausian for specular term ⚬ No geometry term to improve rim light effect ⚬ Smoother specular than GGX ￭ Future works ⚬ Ambient specular ⚬ Modify fresnel term to match with direct light 7
- 8. Goal of my approach ￭ Shading model for every types of fabrics ⚬ From cotton to velvet ⚬ Easy to use for artists ￭ Technical perspective ⚬ Oren-nayar diffusion ⚬ Specular term for fabrics ⚬ 2 colors specular ⚬ Fresnel term which is toward to light direction 8
- 9. Limitations of Unreal Engine shader ￭ Hard to implement custom shading model ⚬ Diffuse shading: Lambert ⚬ No way to change specular model ￭ Base Color slot can be only available slot to input custom shading code, but ⚬ The value is clamped as 0.0 - 1.0 ⚬ Range of value is too narrow to use specular light Fortunately, fabrics do not need strong specular, so its specular can be implemented to Base Color 9
- 10. My approach - Diffuse term (1) ￭ Oren-nayar diffuse shading ⚬ Based on Pope Kim’s approximation ⚬ It is not matched with real Oren-nayar shading, but its quality is great, cheap and easy to implement ￭ Removing (n∙l) from the original code 10 1
- 11. My approach - Diffuse term (2) ￭ Replace (n∙l) to 1.0 ￭ Output value multiplys Base Color ￭ If surface is smooth(Roughness = 0.0), than uses Unreal default diffuse shading 11
- 12. My approach - Specular (1) (Fresnel Term × Specular) + Fiber Scatter ￭ Fresnel Term ⚬ Fuzz on rim part ￭ Specular Term ⚬ Customized inverse gausian specular ⚬ For describing back scattering ⚬ Secondary specular lobe ￭ Fiber Scatter Term ⚬ For describing front scattering ⚬ Primary specular lobe 12
- 13. My approach - Specular (2) ￭ Fresnel term ⚬ Based on Schlick Fresnel approximation1 ⬝ ⚬ Modified 5th power of 1 - cosθd to 4th power for increasing rim lighting effect 13
- 14. My approach - Specular (3) ￭ Specular Term ⚬ Based on The Order’s approach ⬝ iverse gausian specular ⚬ Not related with Roughness value, but much simpler equation ⬝ Result is simiral with The Order’s approach when Roughness value is 1.0 ⬝ I premise every non-metal fabrics’s roughness value is 1.0 If fabric surface has lower roughness than 1.0, using Unreal default specular term Primary specular is implemented in Fiber scatter term ⚬ Masking fresnel term and it induces light direction toward rim lighting 14
- 15. My approach - Specular (3) ￭ Roughness value ⚬ GGX: 0.65 ⚬ The Order: 1.0 ⚬ My approach: 1.0 15
- 16. My approach - Fiber Scatter Term (1) ￭ Fiber Scatter Term ⚬ Wrap lighting for front scattering ⬝ Week transmission effect for the eye facing surface ⬝ Can be used as a secondary specular color for metal fabrics such as Silk or stain ⚬ Linear interpolation between two types of fresnel ⬝ First one is wider ⬝ Second one is narrwer ⬝ Blend them by fabric scatter amount value Can describe from fuzzy cotton to smooth denim ⬝ Fabric scattering color is multiplied to this value 16
- 17. My approach - Fiber Scatter Term (2) ￭ Wrap lighting 17
- 18. My approach - Fiber Scatter Term (3) ￭ Linear interpolation between two types of fresnel 18
- 19. My approach - Final 19
- 20. Result - Fabric scatter amount compare ￭ Define which part will use fabric scatter color ⚬ If the value is 0, than rim part will use fabric scatter color ⚬ If the value is getting increased, area of fabric scatter color is getting wider ⚬ If the value is 1.0, most of surface is fabric scatter color and rim part is base color 20
- 21. Result - Fabric examples (1) 21 Cotton Velvet
- 22. Result - Fabric examples (2) ￭ Hint to make good look fabric material with my approach ⚬ Set Metalic value for ratio of silk fibers in the fabric ⚬ Only Metal fabrics can have lower Roughness value than 1.0 ⚬ Do not use Normal map to describe patterns on silk surface ⬝ Using different values of Roughness for pattern and non-pattern part 22 Satin
- 23. Recomend values for fabrics 23 Fabric Types Metalic Roughness Fabric Scatter amount Cotton or ordinary fabrics 0 1 0.5 Velvat 1 1 0 Silk, Satin 0.8 - 0.9 0.35 - 0.7 1
- 24. Bibliography ￭ Page 3 ⚬ image 1: http://www.apparelsearch.com/fibers.htm ⚬ image 2: http://www.trimfabric.com/nv-97.html ￭ Page 4 ⚬ image 1: https://www.asahi-kasei.co.jp/fibers/en/cupro/what/function1.html ⚬ image 2: https://quizlet.com/92490419/intro-2-textiles-test-1-flash-cards/ ⚬ image 3: https://quizlet.com/92490419/intro-2-textiles-test-1-flash-cards/ ￭ Page 5 ⚬ image 2: https://wallpaperscraft.com/download/silk_material_soft_light_50576/3840x2160 ￭ Page 6 ⚬ image 1: http://www.bloomsburgcarpet.com/resources/weave-structures ⚬ image 2: http://www.textilestock.in/productdetail/47/Fabrics-HomeFurnishingFabrics-Velvet-Velvet-Stock.html 24
- 25. Bibliography ￭ Page 7 ⚬ citation 1: Neubelt, David, Matt Pettineo, and Ready At Dawn Studios. "Crafting a Next-Gen Material Pipeline for The Order: 1886." part of “Physically Based Shading in Theory and Practice,” SIGGRAPH (2013). ￭ Page 10 ⚬ citation 1: http://www.slideshare.net/blindrenderer/rendering-tech-of-space-marinekgc-2011 ￭ Page 13 ⚬ citation 1: Schlick, Christophe. “An inexpensive BRDF Model for Physically-based Rendering.” Computer graphics forum 1 Aug. 1994: 233-246 25