Dissecting the Rendering of The Surge

Dissecting the Rendering of
Philip Hammer
DECK13 Interactive GmbH
Quo Vadis, Berlin, 24.4.2018

Dissecting the Rendering of The Surge
Quo Vadis Berlin 2018
Introduction
● DECK13 Interactive released “The Surge” in 2017
○ New IP, new publisher
○ Overhauled tech (Fledge Engine / 3th Generation)
○ Award Winning: Best German Game, Best Graphics, Best PC-/Console-Game (Deutscher Entwicklerpreis 2017)
○ Our most ambitious game from DECK13

Introduction
● Team of around 70 people in Frankfurt
○ Tech Department: ~11 people (engine + game code)
○ Art- & Sound-Outsourcing
● Myself
○ Since 2006 @ DECK13
○ Working on rendering / engine / graphics / shaders
○ Worked on The Surge, Lords of the Fallen, Venetica, Ankh, Jack Keane, etc.
● The results and techniques presented in this article is
the work of many people in the Deck13 Tech department.

● Fledge Gen 1 (2009: Blood Knights, Tiger & Chicken)
○ PS3, Xbox 360, PC / D3D9, iOS (iPad 2 and up)
○ Deferred Rendering, Direct Lighting only, Minimal Multithreading
● Fledge Gen 2 (2012: Lords of the Fallen)
○ PS4, Xbox One, PC / D3D11
○ Volumetric Lighting, Direct & Indirect Lighting, Task-based multithreaded rendering
● Fledge Gen 3 (2014: The Surge)
○ PS4 (+Pro), Xbox One (+X), PC / D3D11
○ Physically-based rendering, Clustered Deferred Rendering, GPU Particles
● Fledge Gen 4 (2017/2018: The Surge 2)
○ Vulkan, D3D12
○ Currently in the making .. stay tuned
Tech Evolution

● Fledge Gen 1 (2009: Blood Knights, Tiger & Chicken)
○ PS3, Xbox 360, PC / D3D9, iOS (iPad 2 and up)
○ Deferred Rendering, Direct Lighting only, Minimal Multithreading
● Fledge Gen 2 (2012: Lords of the Fallen)
○ PS4, Xbox One, PC / D3D11
○ Volumetric Lighting, Direct & Indirect Lighting, Task-based multithreaded rendering
● Fledge Gen 3 (2014: The Surge)
○ PS4 (+Pro), Xbox One (+X), PC / D3D11
○ Physically-based rendering, Clustered Deferred Rendering, GPU Particles
● Fledge Gen 4 (2017/2018: The Surge 2)
○ Vulkan, D3D12
○ Currently in the making .. stay tuned
Tech Evolution
Today’s topics

Tech Evolution
● The Surge Tech (Gen 3)
○ Stable Framerate across all platforms
PS4: 1080p @ 30 FPS
PS4 Pro: 1620p @ 30 FPS or 1080p @ 60 FPS
Xbox One: 900p @ 30 FPS
Xbox One X: 1800p @ 30 FPS or 1080p @ 60 FPS
○ Physical-Based Rendering
○ Clustered Deferred Rendering
○ Volumetric Lighting
○ GPU Particles
○ Screen-space Reflections
○ etc.
● New things in the making (Gen 4) - short peak into the future towards the end

Physical-based Rendering
● Switched from (non-PBR) Blinn-Phong to
GGX Cook-Torrance BRDF [1]
○ De-facto industry standard.
○ More material data to drive the BRDF
● Artists needed to adapt (Workflow, Tools, Mindset)
○ Lots of pitfalls (no arbitrary texture data)
○ Adoption process was rather unproblematic -
most tools (Substance, Marmoset) already provide PBR workflow
● We use “Metalness-Workflow”
○ Artist provide Albedo, Normal, Roughness and Metalness textures
○ Metalness is a mask to treat the albedo differently in specular lighting

● Direct Lighting: 100% dynamic lights
○ 16 shadowmaps rendered into atlas (4kx4k - 8kx8k, D16_FLOAT)
○ If cap reached, the shadowmap isn’t updated anymore and
virtually becomes static
● Image-based lighting
○ Precomputed, parallax corrected environment probes (Artist placed)
○ Specular probe is 256x256 cubemap (BC6_UFLOAT)
with GGX filtered importance sampled mip chain [2]
○ Diffuse lighting is simply the 6th mip level of probe
(“incorrect”, but visually equivalent with proper irradiance)
○ IBL pass can be modified with simple, multiplicative “ambient lights” [3]

● G-Buffer breakdown

X Y Z W
RT0 (8:8:8:8) Albedo RGB Material-ID
RT1 (10:10:10:2) VS Normal XYZ -
RT2 (8:8:8:8) Roughness Metalness Occlusion [shared]
RT3 (16:16) Motion Vectors XY - -

● Material-ID indexes directly into StructuredBuffer to query per-material data
○ Save G-Buffer space
● [shared] - per-pixel context dependent
○ mutual exclusive material data
○ based on per-material data
○ Emissive Mask
■ Defines whether or not to interpret albedo as emissive
■ Emissive combined in final “combine” pass
■ Effectively saves dedicated emissive channel
○ Translucency

Clustered Deferred Rendering
● Switch from rasterization-based light volume rendering to full (async) compute-based approach
○ Low CPU overhead
■ Light culling runs entirely on GPU
■ Filling a buffer with light infos instead of dispatching thousands of drawcalls
○ Advantages on GPU
■ No need to fetch G-Buffer for every light
○ Async Compute: Lighting runs in parallel to shadow rendering (at least on consoles)
○ But: many more optimizations necessary to get better perf
● Could render environment probes in the same pass
○ Environment probes are still clustered but rendered in a separate (pixelshader) pass together with SSR

Clustered Deferred Rendering
● Divide view frustum into a 3D grid
○ In our case: 16 x 8 x 24
● Culling: Assign lights to grid cells
○ Upload light culling info to GPU (StructuredBuffer with Position, AABB, etc.)
○ Create list of light indices for each cell (single large uint buffer)
● Dispatch lighting compute shader
○ In fact we dispatch twice: unshadowed and shadowed lights
○ Unshadowed can run in parallel with shadowmap generation
● Can use cluster information also for forward rendering
○ We do this for our lit transparent objects
○ Simply compute grid cell index for a position and query light list

Deferred Decals
● Decals play a major role in our environment art
○ Static: Logos/Signs, Material Layers (Sand, Water Puddles, Rust, etc.), Color Variations
○ Dynamic: Blood, Explosion Marks, etc.
● Extremely flexible
● Break uniform look of heavily instanced scenes
● Adds lot of large- and small-scale details

Deferred Decals

Deferred Decals
● Modifies G-Buffer by alpha-blending onto it
○ Therefore, lighting is “free” since it’s done afterwards
● 2 methods for tangentspace reconstruction
○ Surface Normal (use G-Buffer normal)
○ Planar (use decal projection direction)
● Full PBR support + many per-decal features (add. Mask, UV modifiers, etc.)
● Implementation rasterization-based deferred
○ Rasterize geometry (boxes) for each decal
○ CPU bottleneck with large number of decals

Deferred Decals
● Common issue with Deferred Decals: Wrong Mip Selection due to screenspace gradients
○ Problem: Texture leaks around depth discontinuities

Deferred Decals
● Common issue with Deferred Decals: Wrong Mip Selection due to screenspace gradients
○ Problem: Texture leaks around depth discontinuities
○ Common solution: Use highest mip
■ Causes flickering in distance due to oversampling (no mips)
■ Texture cache hit
○ Our solution: Use mip0 only with large depth discontinuities
// Sample 2 quads
const float4 d0 = depthSampler.Gather(sampler_point_clamp, screenUV, int2(-1, -1));
const float4 d1 = depthSampler.Gather(sampler_point_clamp, screenUV, int2(0, 0));
const float4 dCross = float4 (d0.z, d0.y, d1.y, d1.z);
const float dC = d.w;
// Find suitable neighbor screen positions in x and y so we can compute proper gradients
// Select based on the smallest different in depth
const bool useFirstMip = any(abs(dC.xxxx - dCross) > 0.001);
if (useFirstMip)
albedoTex.SampleLevel(..);
else
albedoTex.Sample(..);
d0.x d0.y
d0.z d0.w
d1.x d1.y
d1.z d1.w

“Object Decals”
● Alternative Term: “Blend Meshes”
● Alpha-Blend arbitrary meshes on the G-Buffer
○ Artists can create simple plane-”decals” with custom UV setup
○ Efficiently add small, high-res details like panels, rivets, LED, etc.
○ Works also on skinned objects (e.g. logos on Exo-Gear)
1 Base G-Buffer Pass (solid)
2 Object Decal Pass (alpha-blend)
3 Deferred Decal Pass (alpha-blend)

Next Decals / Fledge Gen 4
● “Bindless” Decals
○ Analogous to clustered deferred lighting
■ Culling & rendering happens entirely on the GPU
■ Collect info about all visible decals in a buffer
■ Render all decals before lighting in the same compute shader
○ Decal info stores texture IDs (UINT32) to index directly into DescriptorSet / DescriptorTable
○ Blending not restricted to alpha-blending anymore (linear interpolation)
■ “Geometric” normal blending possible [4]
■ Replacing layered materials with decals is now feasible
○ Availability of interpolated vertex-normals in G-Buffer improves T-Space reconstruction
○ Currently in active development

Optimizing for Occupancy / GCN
● GCN Hardware wants saturated CU Units
○ Huge lighting shader uses a lot of general purpose registers
if not structured carefully
● Reducing register usage (VGPR/SGPR) can be a huge win
○ Especially for long, ALU heavy shaders such as lighting
○ Minimize register lifetime
○ Look at the data and iterate
■ runtime profilers
■ static shader code analysis statistics
● Goal: Want min. 40% GCN Wave Occupancy on
PS4 and Xbox One (for lighting compute shader)

Optimizing for Occupancy / GCN
● Example: Split light type loops
○ Different light types uses different data
■ Shadowed lights use shadow projection matrices, shadowmaps, etc.
■ Image projectors use image projection matrices, images, etc.
■ Boxlights must check bounds differently
■ etc.
○ Shader can free up register usage if structured well
for each light in lightbuffer
if light.type == POINT
// do pointlight calculations
if light.type == SPOT
// do spotlight calculations
else if light.type == SPOT_SHADOWED
// do shadowed spotlight calculated
end
for each light in lightbuffer_point
// do pointlight calculations
end
for each light in lightbuffer_spot
// do spotlight calculations
end
for each light in lightbuffer_spot_shadowed
// do shadowed spotlight calculations
end

What’s next ?
● Currently working on Fledge Gen 4
○ Always improving tech iteratively
○ Always keep existing systems “alive”
○ Parallel Development of new systems / breaking changes
● Spread knowledge
○ Weekly presentation meeting (tech internal)
● Leap to new APIs
○ Vulkan, DirectX 12

What’s next ?
● New low-level renderer design
○ Better match the new APIs (no more state-driven)
○ More low-level control such as explicit resource syncs, GPU memory management, etc.
○ Async-Compute also on PC
○ More C-style, more data-oriented
○ “Do as little as possible during render-loop” aka “prebake as much as we can”
■ Setting DescriptorSets, Map/Unmap GPU memory, etc.
○ Goal: Rendering must not be a CPU performance bottleneck
● Better ingame-profiling for content creators
● Better tools for artists and game designers

What’s next ?
● Improving specific rendering subsystems
○ Switch to physically based inverse square falloff (lumen units)
○ Improved IBL system (e.g. split irradiance and specular probes)
○ Unified volumetric fog / lighting (“lit fog” vs. “volumetric lighting”)
○ Bindless Decals
○ New material system
■ More flexibility for custom shaders / FX Materials
■ Better fit for the new rendering backend interface
○ Improved postprocessing, Antialiasing, HDR tonemapping / color correction

Thank you for
your attention!
DECK13 is hiring!
● Tools Programmer
● Concept Environment Artist
● VFX Artist
● etc.
@philiphammer0
phammer@deck13.com
linkedin.com/in/philip-hammer-430baa6

References
[1] Walter et al., "Microfacet Models for Refraction through Rough Surfaces"
[2] Karis, “Real Shading in Unreal Engine 4”, Siggraph 2013
[3] Schulz, Mader, “Rendering Techniques in Ryse: Son of Rome”, Siggraph 2014
[4] Barré-Brisebois, Hill, "Blending in Detail"
http://blog.selfshadow.com/publications/blending-in-detail/

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