Shader, The Unknown
at UnityWTB - by @doppioslash - 26/03/2016
Hi, I'm
Claudia Doppioslash
@doppioslash
Functional Programmer
GameDev
&
Shader Programmer on CyberCook (iPad&VR)
I write
www.shadercat.com
A site about Shaders, Rust,
and Graphics Programming
@shadercat
Why make your own custom shader(s)?
Why make your own custom shader(s)?
Unity 5 has got a pretty decent default shader system
Why make your own custom shader(s)?
But!
Why make your own custom shader(s)?
Journey's look was not achieved with a standard shader.
Why make your own custom shader(s)?
Optimise for a specific target platform
(Like VR)
Why make your own custom shader(s)?
- more work
- needs thought
- needs time from the artists
- needs to study those Graphics papers!
Drawbacks:
So what is a shader?
So what is a shader?
"A piece of code that runs on the GPU, takes vertices, textures, and other data, and returns pixel colours"
So what is a shader?
Pipeline
scene -> objects with the same material ->
So what is a shader?
Pipeline
drawcall -> list of vertices & other info ->
So what is a shader?
Pipeline
vertex shader -> fragment + interpolated data ->
So what is a shader?
Pipeline
fragment shader (lighting) -> final pixel color
(An aside)
Renderer Types
Renderer Types
-> (See GDC 2016)
- Forward
- Deferred
- Forward+
- Object Space
Renderer Types
Forward
Shading happens at each object's raster time
One pass for each light
Expensive when many lights
But good support for complex lighting
Unity supports it
Renderer Types
Deferred
Shading happens last, once
First rasterises the objects data into 2d buffers
Cheap when many lights
Limited support for complex lighting
Unity supports it
Unity Shaders Basic
Unity Shaders Basic
Each material has a shader assigned
Unity Shaders Basic
The language is Cg (NVIDIA) + ShaderLab
Unity Shaders Basic
Pre-filled templates
Unity Shaders Basic
Surface Shaders give you:
- easier normal mapping
- helper functions
- add passes for forward renderer
Occasionally it's in the way.
But!
Unity Shaders Basic
Surface Shaders Anatomy
Unity Shaders Basic
Properties:
We can also build custom inspector editors
Unity Shaders Basic
Properties Custom Inspector
Unity Shaders Basic
Subshader
Unity Shaders Basic
Structs
Unity Shaders Basic
Structs
- limited slots
- data from the various phases has to go through them
Unity Shaders Basic
Surf function
Unity Shaders Basic
custom lighting function
use the naming convention Lighting<name>
Unity Shaders Basic
(optional) custom vertex shader
Unity Shaders Basic
The Standard shader implementation can be downloaded
Unity Shaders Basic
The include files are important to interoperate with Unity shadows/lightmaps
Pre-PBS principles
Non-PBS principles
In the olden days...
- diffuse
- specular
- normal
- texture BRDF lookup
- fresnel
we lacked ALU power to do complex lighting
Parts of the shader
Diffuse = dot(N,L)
lacks a model of the surface behaviours
it can give back more light than it receives
dot product of the Normal and Light directions
Parts of the shader
Diffuse = dot(N,L)
Parts of the shader
Normal Mapping
is still largely the same
a way to add cheap detail with one texture
Parts of the shader
Specular
depends just on direction and specular map
no concept of Roughness
Specular Power :/
PBS principles
PBS principles
Linear
PBS principles
Linear
PBS principles
Linear
PBS principles
Linear
mobile toLinear
mobile toGamma
PBS principles
HDR
PBS principles
HDR
Many operators for Tone Mapping
[Ref: filmicgames.com ]
Reinhard
plain linear &
exposure adjustment
PBS principles
The Rendering Equation
[Ref: @levork ]
(using only 1000 most used English words)
PBS principles
The Rendering Equation
[Ref: Raytracing Lecture ]
PBS principles
Microfacet theory
Introduces a good explanation of Roughness
Surfaces have micro-facets
each reflect light according to its normal
PBS principles
Microfacet theory
[Ref: Moving Frostbite to PBR ]
In a picture
PBS principles
Energy conservation
More intense highlight are smaller
Less intense are larger
Can't reflect more light than received
PBS principles
Area Lights
Sadly no realtime support in Unity
More expensive but more realistic
PBS principles
More accurate BRDFs
- Oren Nayar
- Cook Torrance
- Ashikhmin Shirley
- and many more...
PBS principles
Indirect light
Prefiltered CubeMaps
Global Illumination
Physically Based Process
Normal Process:
fail and no idea why
Physically Based Process
You've got nothing to compare with except your own imagination.
And small errors can pile up unseen
PB Process:
fail and know why/where
by comparing with ref
Physically Based Process
PB Process:
same settings will work with different lighting conditions
Physically Based Process
Different BRDFs
for Different surfaces
Lambert
Different BRDFs
Diffuse only
Plainest
Very cheap
Ok for matte plastic surfaces
Oren Nayar
Different BRDFs
Adds a roughness model
Diffuse only
Pretty decent for skin, cloth
(even not using Subsurface Scattering)
Blinn
Different BRDFs
plastic
with energy conservation it's a viable choice
Cook Torrance
Different BRDFs
flexible, good all around
there are better BRDFs for metal
A great specular
Ashikhmin Shirley
Different BRDFs
Excellent for metal
Anisotropic
As an extra layer for wet surfaces
Disney
Different BRDFs
onesize fits all
maybe easier for artists but not as flexible
they chose to keep the fewest parameters possible
Drawbacks to choosing unusual BRDFs:
BRDFs window shopping
Indirect lighting calculation can be tricky
But using one for a more common BRDF could work ok
Artist facing decisions
Artist facing decisions
more configurability means more confusing for the artist
need to figure out which parameters are less relevant
Unity Frame Debugger
BRDF Demonstration
Let's shade some heads in Unity...
Conclusion
Now you have the basics to tackle making your own custom lighting system.
References
Find them at:
That's all folks!
@doppioslash
@shadercat
See you on twitter :)
Shader, The Unknown - UnityWTB 2016
By Claudia Doppioslash
