Automated Combination Of Real-Time Shader Programs

Abstract

Presentation of Research Paper "Automated Combination Of Real-Time Shader Programs"

Full text

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 1
Automated Combination
Of Real-Time Shader Programs
Matthias Trapp :: Jürgen Döllner
+=

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 2
Outline
1. Motivation & Overview
2. Concept
3. Tagging Shader Source Code
4. Preprocessing Step
5. Shader Combination
6. Conclusions

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 3
1. Motivation & Overview
Problem:
•Fixed-function pipeline is obsolete
•Functionality is provided by shader programs
•Combine functionality →combine programs
Goals:
•Minimize shader permutations
•Dynamic configuration of combined programs
•Keep functionality of individual shaders
•Enable nesting of shader programs
Applications
•Shader-driven rendering engines
•Emulate orthogonal fixed function pipeline features
•Dynamic material systems

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 4
1. Motivation & Overview
Example Scenegraph
Texture
Normal
X-Ray
Shapes
Texture Shader
Color Map
Normal Shader
Normal Map
Root
Fog Shader
Phong Shader
X-Ray Shader

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 5
Next
1. Motivation & Overview ✓
2. Concept
3. Tagging Shader Source Code
4. Preprocessing Step
5. Shader Combination
6. Conclusions

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 6
2. Concept - Overview
•Straightforward modular principle:
•Basically: Dynamic uber-shader construction
•Exploits static branching to control execution paths
•Main phases:
1. Decomposition shader into shader handler (next)
2. Preprocessing of shader handler to intermediate shader source
3. Combination of intermediate shaders to a single uber-shader
Shader ProgramA
Vertex ShaderA
Geometry ShaderA
Fragment ShaderA
Shader ProgramB
Vertex ShaderB
Geometry ShaderB
Fragment ShaderB
Shader ProgramC
Vertex ShaderC
Geometry ShaderC
Fragment ShaderC
=
+

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 7
2. Concept - Decomposition
•Shader functionality is split into handler with predefined semantics
•Shader handler can work on global context (interface)
Shader ProgramA
Vertex ShaderA
Geometry ShaderA
Fragment ShaderA
Vertex ShaderA
void main()
{
vec3 N, L;
vec4 D, A, GL;
float NdotL;
N = gl_NormalMatrix * gl_Normal;
L = vec3(gl_LightSource[0].position);
D = gl_FrontMaterial.diffuse *
gl_LightSource[0].diffuse;
A = gl_FrontMaterial.ambient *
gl_LightSource[0].ambient;
GL = gl_LightModel.ambient *
gl_FrontMaterial.ambient;
NdotL = max(dot(normalize(N),
normalize(L)), 0.0);
gl_FrontColor = NdotL * D + GL + A;
gl_Position = ftransform();
}
Vertex ShaderA
VertexShaderHandlerA1
VertexShaderHandlerA2
onLighting
onTransform

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 8
2. Concept - Combination
Shader ProgramC
Vertex ShaderC
Geometry ShaderC
Fragment ShaderC
Vertex ShaderA
VertexShaderHandlerA1
VertexShaderHandlerA2
Vertex ShaderC
Vertex ShaderA
VertexShaderHandlerA1
VertexShaderHandlerA2
Vertex ShaderB
VertexShaderHandlerB1
VertexShaderHandlerB2
VertexShaderHandlerB3
VertexHandler Controller

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 9
2. Concept –Decompostion Details
•Shader: is an ordered set of shader handler (SH)
•Prototype (P)
•Represents an atomic functionality
•Assigned to a shader handler: P = prototype(SH)
•Prototype List (PL)
•Defines explicit order upon prototypes
•Important for handler combination
•P& PL
•Must be declared by developer in advance
•Differ for each shader type (vertex, fragment, …)
onAnimation
onLighting
onTransform
onLighting
onTransform
onAnimation

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 10
2. Concept –Interfaces
Properties
•Shared state between shader handler
•Depend on shader type
•Must be defined in advance
•Deposited as source code in specific shading language
GLSL Examples
struct us_VertContext
{
vec4 us_Position;
vec3 us_Normal;
float us_PointSize;
vec4 us_ClipVertex;
} vertContext;
Vertex Handler Interface
struct us_FragContext
{
vec4 us_FragColor;
vec3 us_FragNormal;
vec3 us_FragView;
vec3 us_FragLight;
gl_MaterialParameters us_FrontMaterial;
float us_FragDepth;
} fragContext;
Fragment Handler Interface

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 11
2. Concept –Execution Modes
•Control shader handler execution
•Propagate active state of program
→Activate handler according to execution modes
•Can be configured at runtime for each handler
•Handler execution modes:
•Local: handler is invoked only if the program object is active
•Global: handler will always be invoked
•Optional: invoke handler if no handler of resp. prototype is active
•Explicit: all other handler of this prototype will be disabled
•Ignore: handler will never be invoked

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 12
2. Concept –Execution Modes
Example Scenegraph
Texture
Normal
X-Ray
Shapes
Texture Shader
Color Map
Normal Shader
Normal Map
Root
Fog Shader
Phong Shader
X-Ray Shader

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 13
Next
1. Motivation & Overview ✓
2. Concept ✓
3. Tagging Shader Source Code
4. Preprocessing Step
5. Shader Combination
6. Conclusions

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 14
3. Tagging Shader Source Code
Extend shading language grammar (here GLSL)
Shader Handler Example:
handler [local|global|optional|explicite|ignore] hName (interface iName)
handler local onLighting(interface context)
{
vec3 fragNormal = normalize(context.us_FragNormal);
vec3 fragView = normalize(context.us_FragView);
vec3 fragLight = normalize(context.us_FragLight);
vec3 reflection = normalize(reflect(-phongLight, phongNormal));
float NdotL = max(0.0, dot(fragNormal, fragLight));
float VdotR = dot(fragView, reflection);
float VdotRExp = pow(max(0.0, VdotR), context.us_FrontMaterial.shininess);
context.us_FragColor =context.us_FrontMaterial.ambient *
(gl_LightSource[0].ambient +gl_LightModel.ambient) + NdotL *
gl_LightSource[0].diffuse *context.us_FrontMaterial.diffuse +
VdotRExp * context.us_FrontMaterial.specular *
gl_LightSource[0].specular;
return;
}

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 15
Next
1. Motivation & Overview ✓
2. Concept ✓
3. Tagging Shader Source Code ✓
4. Preprocessing Step
5. Shader Combination
6. Conclusions

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 16
4. Preprocessing Step
•Transforms tagged source into:
•Intermediate source code (language specific)
•Mapping: Shader Handler →Prototype
•Basically via token substitution:
•Insert specific interface source code
•Result is ready for API shading language front-end compiler

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 17
Next
1. Motivation & Overview ✓
2. Concept ✓
3. Tagging Shader Source Code ✓
4. Preprocessing Step ✓
5. Shader Combination
6. Conclusions

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 18
5. Shader Combination
•During Pre-traversal by Shader Management System (SMS)
•Create priority program list (PPL)
•Create controller for each shader type:
•Generated controller configured by an invoker table
•Array of Boolean variables represents activity-state of handler
•Passed to the controller as uniform shader state
•During evaluation of a shader program:
•Activate/deactivate shader handlers by modify invoker tables
•With respect to the handler execution modes
foreach prototype P

PL do
foreach shader program SP

PPL do
foreach shader handler SH

SP do
if (prototype(SH) = P) do
appendIfStatement(SH)
SH1SH5SH0SH6
SH3SH7SH2SH8SH4
UberShader
PH0PH1PH2PH3PH4
Prototype Handler Table
SH1
SH0SH2
Shader Handler
Program 0
SH3SH4SH5
Program 1
SH6SH7
Program 3
SH8
...
Sort

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 19
6. Conclusion
Summary
•Combination of shader programs
•Generic uber-shader construction
•Control parameter for execution logic
Drawbacks
•No automatic shader decomposition
Future Work
•Resource management for shader state
•Optimize generated programs for fixed execution paths
•Enable the usage of LoD shader handler

:: Matthias Trapp :: Jürgen Döllner :: Automated Combination Of Real-Time Shader Programs :: 20
Thank You.
matthias.trapp@hpi.uni-potsdam.de
juergen.doellner@hpi.uni-potsdam.de
:: www.hpi.uni-potsdam.de ::