A Crash Course in HLSL

1
A Crash Course in HLSL

• Matt Christian

2
Agenda

• About Me
• What is HLSL?
• What is a Shader?
• Vertex Shaders
• Pixel Shaders
• Geometry Shaders
• HLSL/Shader History
• How Does It Work?
• HLSL Code Segments

3
Agenda (Contd)

• Shader Examples
• Implementing a Simple Shader
• Shader Overview
• Engine Implementation
• Post Processing Shaders
• Conclusion
• Web Links
• Extras

4
About Me

• Student at University of Wisconsin Stout
• Studying Applied Mathematics and Computer
  Science Software Development
• Graduated with honors from Northcentral Technical
  College
• Associates Degree in Computer Programming 2006
• Avid gamer and general game development junkie

5
What is HLSL?

• Microsofts HLSL (High Level Shader Language) is
  a simple language used to write shaders.
• Used with DirectX to provide high-end graphics
• Slightly comparable to a high-level C

6
What is a Shader?

• A shader is a program (code file) that is
  executed on the GPU (Graphics Processing Unit
  graphics card) to manipulate the data before it
  is drawn to the screen.
• Can be written in numerous shader-specific
  languages
• HLSL (DirectX), GLSL (OpenGL), Cg (nVidia),
  Assembly
• Math-Heavy (Algorithms)

7
Vertex Shaders

• Shader run on per-vertex level
• Examples
• Color
• Texture
• Position
• Do not change the data type

8
Pixel Shaders (Fragment Shader)

• Run per-pixel
• Examples
• Lighting Values
• Output certain color
• Cannot produce complex effects due to per-pixel
  implementation

9
Geometry Shaders

• Manipulate graphics primitives to create new
  primitives (points, lines, triangles)
• Examples
• Shadow Volumes
• Cube Map (Skybox)
• Newest Shader type, only works in DirectX 10
• OpenGL Extension

10
Shader Examples

• Almost all recent video games use shaders
• All animated CGI movies use shaders (Pixar)
• Some techniques commonly used
• Parallax-Mapping (Bump-Mapping)
• Phong Shading
• Cell-shading
• Bloom
• High Dynamic Range Lighting (HDR)

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Parallax-Mapping
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Phong Shading
13
Ray Tracing (Pre-Rendered)
14
Cell-Shading (Windwaker)
15
Bloom (Tron)
16
High Dymanic Range Lighting (FarCry)
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Combination (Gears of War)
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Combination (Ratatouille)
19
HLSL/Shader History

• Four Generations of GPUs
• Fixed-Function Pipeline
• Released with DirectX 7 (2000)
• Transformation and Lighting (TL) hardware
• Pixar
• RenderMan shading language
• Way to bypass built-in lighting
• Problem with render times
• Programmable Pipeline
• Introduction of programmer defined code (shaders)
• First consumer-level programmable GPU
• Began with DirectX 8 (2001)

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How Does It Work?

• Graphics Pipeline

21
HLSL Code Segments

• Variables
• Float4x4 (4x4 Matrix), float4 (4 row
  vector-matrix), float
• float4 ambientColor 1.0f, 1.0f, 1.0f, 1.0f
  //Color of Ambient Light
• float ambientbrightness 1.0f //Brightness of
  Ambient Light
• Stream Structures
• //App to Vertex Shader
• struct ambientA2V
• float4 Pos POSITION
• float2 TexCoord TEXCOORD0

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HLSL Code Segments (contd)

• Semantics
• String describing the type of data being passed
  between shader stages
• COLOR (Diffuse and specular color), NORMAL
  (Normal vector), TEXCOORD (texture coordinates)
• Like variable type, gives shader heads up
• Use this as the normal vector!
• Functions
• Similar to regular C/C functions but can
  specify return semantic
• float4 ambientPS(in ambientV2P IN) COLOR
• //Get texture
• float4 Color tex2D(TextureSampler,
  IN.TexCoord)
• //Return texture color ambientbrightness
• return Color (ambientColor
  ambientbrightness)

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HLSL Code Segments (contd)

• Techniques
• Considered classes called by the render engine
• Typically contain and run vertex, pixel, and
  geometry shaders using different passes (Passes
  considered class functions)
• Different techniques can be used for different
  hardware configurations to support old/new
  hardware
• Intrinsic Functions
• Built-in, commonly used (usually math-related)
  functions often similar to assembly
• Mul(x, y) (multiplies x y)
• Abs(x) (absolute value of x)

24
Implementing a Simple Shader

• Example Setup
• Shader Ambient Light with Point Light
• Technique PointLight
• 2 passes
• Engine C and DirectX 9.0c

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Shader Overview

• 2 lighting algorithms
• Ambient Light
• Point Light
• Pass P0
• Create Point Light
• Pass P1
• Create Ambient Light
• Code

26
Engine Implementation

• Code

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Post Processing

• Render to a target (texture)
• Manipulate Texture
• Display Texture as Render
• Examples
• Motion Blur
• Bloom
• Image Perturbation (Heat waves)

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Conclusion

• Shaders provide current/next gen graphics by
  fully utilizing the GPU using code algorithms
• Vertex Shader
• Pixel Shader
• Geometry Shader
• Relatively new, still developing
• Questions?

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Web Links

• HLSL MSDN
• http//msdn.microsoft.com/en-us/library/bb509561(V
  S.85).aspx
• DirectX SDK
• http//msdn.microsoft.com/en-us/directx/aa937788.a
  spx
• Cg Book
• http//developer.nvidia.com/object/cg_tutorial_hom
  e.html
• My Site
• http//www.insidegamer.org/Projects.aspx
• http//www.geekswithblogs.net/CodeBlog

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Extras

• How does a shadow volume work?
• Create rays pointing from geometry to infinity
• Everything within this larger geometric shape is
  encased in shadow, everything outside is lit
• Determine faces aiming towards/away from lighting
• Fringe creates silhouette
• Cast rays from silhouette vertices away from
  light to infinity to generate shadow volume
• Optional Place caps to optimize

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Shadow Volume (Doom 3)
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Extras (Contd)

• How does bump mapping work?
• Create a heightmap texture
• Apply to a model prior to lighting (same as
  applying any texture to the model)
• Use trig to determine the surface normal per
  pixel
• Any lighting algorithm will calculate the new
  shadows based on surface normals