Gpu presentation

Graphics Programming with Unity3D Jonathan Moore [email_address]

The GPU
Highly Parallelized
Performs Vector, Matrix, and Texture lookup operations at fast speeds
But comes with limitations
not as flexible as the CPU
rigid levels of communication
Limited forms of data output
but this is changing with newer Graphics APIs
DirectCompute, OpenCL, and CUDA allow more general usage of the GPU

Two main access points in Unity
Shading
The conversion of 3D models into 2D-space (your screen) with the graphics pipeline
Lighting, Bump Mapping, Toon Shading, etc
Post-Processing
performing shader operations on the image that is about to be drawn to the screen to achieve certain effects
Motion Blur, Depth of Field, SSAO, etc

The Pipeline

A 3D Model
Most important parts:
A collection of points (vertices)
The triangles that are drawn on those points
Additional information:
Uv coordinates for Texture look-ups
2 sets (can be swapped with Unity's importer)
Normals
Important for lighting
Tangents
used for bump mapping

The Vertex Shader
Responsible for transforming vertex coordinates
Passes information to pixel shader
normals, uvs, vertex lighting, custom information
information is interpolated between the 3 vertices of a triangle
The vertex shader can often help obtain less accurate effects at a lower cost
vertex lighting vs. pixel lighting

The Pixel Shader
Responsible for outputting a color for each triangle fragment
Largely color-focused (usually returns a half4)
Texture Look-ups, adding bump map shading, compositing
note that the GPU utilizes a half data type
Runs ~10x as many times as vertex shader
that number may increase with newer shader pipelines

Sample Code!

Types of Lighting
Flat
Normal is uniform for each triangle
Vertex / Gouraud
Lighting is calculated in vertex shader for each normal and then interpolated
Pixel / Phong
Lighting is computed per fragment by having the normals interpolated
most expensive

Types of Lighting

Shaderlab
Not shader code???
Not that complicated, but can tend to abstract things too much
CG code is injected into it when more control is needed
Fairly well described in the Unity documentation
Also serves as wrapper for your shaders, so don't ignore it!
Especially Colormask RGB, Cull Off, etc

Multi-pass Rendering
The other reason why you should care about Shaderlab
Essentially allows you to draw the model multiple times and combine the results together
Fairly well described in the Unity documentation
Unity uses this to combine lighting equations
Can be used for your own devices
Transparency + Glow

More Sample Code!

Image Effects
Some effects can happen by changing the screen in 2D space before it gets displayed
Part script, part shader
Unity has a script in Pro Standard Assets that the script can inherit from
OnRenderImage and Graphics.Blit are the key
Graphics.Blit will apply the material to the image, in this case that material will have a shader set up to do the image effect

Image Effect Sample Code!

Image Effect “Hacks”
Use them to do calculations outside of OnRenderImage
I've used them to do texture combination and interpolation
Remember that GPU is stupid fast
Create a buffer by rendering to a texture and then using that with a screen space effect
Distortion particle effect
Render with replacement is a powerful Unity feature (see camera docs)

More Image Effect Sample Code!

The Future: Unity 3.0
Deferred Rendering
Huge improvement over Multi-pass
More dynamic lights per scene
Access to G-Buffer
Shaderlab
Supposedly being revamped to make it easier to use (according to Aras)
Occlusion Culling
Helps prevent hidden objects from wasting processing

The Future: DX11+ OpenGL 4.0
Tessellation is apparently the future
Adding geometry to meshes in real time to give them more details and better lighting
Allows for models much closer to the quality of animated movies
New Shader Pipeline
The future grows the number of programmable shaders from 3 to 5
Vertex Shader -> Tesselation Shader -> Hull Shader -> Geometry Shader -> Pixel Shader

Additional Resources
NVIDIA developer zone
The CG Tutorial
GPU Gems (legendary for a reason)
Real Time Rendering (Akenine-Moller)
ShaderX books (similar to GPU Gems)
SIGGRAPH White Papers
Unite Presentations
Several on shader tips and tricks

Thats all folks! [email_address] jonmoore.squarespace.com

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