Chapter 5: DirectX®
Chas. Boyd
Outline
• What drove the language design?
• Background
• What does it look like?
• Syntax definition
• How does it work?
• API integration
• How is it used?
• Effects Framework
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Background
• The DirectX® Process
• Evolution of DirectX®
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Industry Process
• Based on iteration with partners
• Requirements from software developers
• Feasibilities from hardware developers
• Combine to deliver product for
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programmers
Pipelined to work in parallel
Relies on Reference Implementation
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Direct3D Reference
• Software model of hardware
• Analogous to/input to “C” model stage of
hardware design
• Acts as “compilable specification:”
• Used to communicate new features and
requirements to IHVs
• Provided as comparison to ISVs
• to check behavior of drivers while coding
• Used to test drivers for conformance
• Color rules by Jim Blinn
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Industry Process
DirectX
Team
Hardware
Vendors
DirectX
Components
New Hardware
Software
Developers
End Users
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DirectX Evolution
DX9 Float Pixels
DX8.1 More Shaders
DX8 Programmability
DX7 Hardware T&L
DX6 Multi-Texture
DX5 DrawPrim
DX3 1st Direct3D
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DirectX Graphics Architecture
Vec0
Vec2
Vec3
Vertex
Shader
VB
Pos
Image
Surface
Vec1
Color
TC1
Tex0
Primitive Ops
Tex1
Pixel
Shader
Tex2
Samplers
Output pixels
Vector
Data
Geometry
Ops
TC2
Vertex
Components
Pixel
Ops
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Vertex Shader
Vec0
Vec1
Vec2
Vec3
Vec4 … Vec15
A0
R0
Const0
R1
Const1
R2
Const2
Vertex ALU
R3
Const3
…
…
R11
Const95
Hpos
TC0
TC1
TC2
TC3
Color0 Color1
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Pixel Shader Architecture
Hpos
TC0
color
TC1
TC2
TC3
d0
d1
constant
texture
Stage0
t0
c0
Stage1
t1
c1
Stage2
t2
Stage3
t3
c3
temp
c4
c2
r0
r1
...
Texture
Stages
Pixel ALU
Pixel
c7
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DirectX® 6 Multitexture
• Texture registers
2-8
• Temp registers
1
• Color registers
2
• Constant registers
1
• Output registers
0
• Instruction count
2-8
• Supports dependent reads
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DirectX® 8 Pixel Shaders
• Texture registers
• Temp registers
• Color registers
• Constant registers
• Output registers
• Instruction count
• +texture address ops
4
2
2
8
0
8
4
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DirectX® 9 Pixel Shaders
• Texture registers
• Temp registers
• Color registers
• Texture Coordinates
• Output registers
• Instruction count
• +texture address ops
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12
2
8
4
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32
• Supports flow control
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DirectX® 9.1 Pixel Shaders
• Texture registers
16
• Temporary registers
16
• Color registers
0
• Texture Coordinates
8
• Constant registers
64
• Output Registers
4
• Instruction count
1024
• Dynamic flow control
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DirectX® 6 API
• Multitexture:
SetTSS( 0, COLOROP, SELECT );
SetTSS( 0, COLORARG1, TEXTURE );
SetTSS( 1, COLOROP, ADD );
SetTSS( 1, COLORARG1, CURRENT );
SetTSS( 1, COLORARG2, TEXTURE );
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Multi-Texture Macros
SETINSTR( 0, SELECT, TEXTURE, * );
SETINSTR( 1, ADD, CURRENT, TEXTURE );
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DirectX® 8 Assembly
tex t0
tex t1
; base texture
; environment map
add r0, t0, t1
; apply reflection
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DirectX® 9 HLL Syntax
outColor = tex2d( baseTextureCoord,
baseTexture )
+ texCube( EnvironmentMapCoord,
Environment );
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Compulsory Figures
• Specular Bump Mapping
• BRDFs
• Procedural Wood
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Per-Pixel Specular
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BRDFs
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Basic Procedural Wood
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Wood with Noise
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2-Hemisphere Model
Sky Color
q
Ground Color
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Hemisphere Lighting
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Hemisphere Result
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Why an HLL?
• Scalability vs hw
• Programming complexity
• Higher Level Language solves these
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Design Goals
• High level enough to hide hardware
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•
•
specific details
Simple enough for efficient code
generation
Familiar enough to reduce learning
curve
With enough optimizing back-ends
for portability
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Design Baseline
• ‘C’ -like syntax
• A standard language
• like c++ or C# or HTML
• in the VS.net IDE
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Graphics Architecture
Application
D3DX
Direct3D
Driver
Assembler, compiler,
effects, utilities
Semantic mapping
Code translation
Hardware
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Preprocessor
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#define
#elif
#else
#endif
#error
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#if
#include
#line
#undef
• Function-style #defines not
supported
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Types
• Basic type is 32-bit float
• Structs and arrays supported
• Typedef to shorthand user defined
•
types
Component access and swizzles
float
float2x1
float3x1
float4x1
float2
float2x2
float3x2
float4x2
float3
float2x3
float3x3
float4x3
float4
float2x4
float3x4
float4x4
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Variables
• Local / global
• Static
• Global variables that are not externally visible
• Const
• Cannot be modified by the shader program
• Can be set external to the program
• Can have initializers
• Can have semantics
• For function parameters
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Operators
• Pretty much all of C operators
• Including ?: and sizeof()
• No new language semantics
• Despite temptation
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Arithmetic operators are per component
Matrix multiply is an intrinsic function
Logical operators are per component
No bitwise operators
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Statement Syntax
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•
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{ [statements] }
[expression] ;
return [expression] ;
if ( expression ) statement [else
statement]
for ( [expression |
variable_declaration] ; [expression] ;
[expression] ) statement
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Intrinsic functions
sqrt
exp2
log2
min
max
abs
len
det
dot
mul
any
value
value
value
value
value
value
float
float
float
value
float
sqrt(value a)
exp2(value a)
log2(value a)
min(value a, value
max(value a, value
abs(value a, value
len(value a)
det(value a)
dot(value a)
mul(value a, value
any(value a)
all
float all(value a)
b)
b)
b)
b)
Square root
Base 2 Exp
Base 2 Log
Maximum
Minimum
Absolute value
Vector length
Matrix determinant
Dot product
Matrix multiplication
Logical OR of all input
components
Logical AND of all input
components
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User Functions
• Standard C-like functions
• Output type and input parameters
• Parameters can be passed by copy
in/copy out mechanism
• in/out declaration
• Inlined internally -no recursion
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Functions (cont.)
• Can be static (not externally
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•
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accessible)
Non-static functions parameters must
have Direct3D declarator semantics
Parameters can be marked const
Parameters can have default
initializers
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Differences from C
• No pointers
• No recursion
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HLSL Summary
• Ease of Use
• Enable software developers
• Consistency of Implementation
• Enable multiple vendors
• Management of Evolution
• Enable multiple generations
• Result:
• Fundamental architecture of DXG
software stack and higher level language
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Application Integration
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Geometry Mapping
• DirectX® 8 Vertex Shaders assume a
data layout
• Decl & shader code are tied together
• Forces shader author to communicate
with geometry provider
• Standard register conventions can help
some
• Complicates combining shaders
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Semantics
• DirectX® 9 decouples decl from VS
• Both decl and VS refer to semantics
rather than register names
• Direct3D runtime connects appropriate
vertex stream data to Vertex Shader
registers
• Key feature of DirectX9 low-level API
• driven by HLSL and shader requirements
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DX8 Vertex Declaration
Strm0
Strm1
Vertex layout
v0
skip
vs 1.1
mov r0, v0
…
v1
Declaration
Shader handle
Shader program
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New Vertex Declaration
Strm0
Strm1
Strm0
Vertex layout
pos norm diff
Declaration
pos norm diff
vs 1.1
vs 1.1
dcl_position v0
dcl_position v0
dcl_diffuse v1
dcl_diffuse v1
mov r0, v0
…
Shader program
(Shader handle)
mov r0, v0
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Vertex Declaration
struct D3DVERTEXELEMENT9
{
Stream;
// id from setstream()
Offset;
// offset# verts into str
Type;
// float vs byte, etc.
Method;
// tessellator op
Usage;
// default semantic(pos, etc)
UsageIndex // e.g. texcoord[#]
}
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VS Input Semantics
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position[n]
blendweight[n]
blendindices[n]
normal[n]
psize[n]
diffuse[n]
specular[n]
texcoord[n]
tangent[n]
binormal[n]
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VS output / PS input
semantics
• position
• psize
• fog
• color[n]
• texcoord[n]
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Uses for Semantics
• A data binding protocol:
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Between vertex data and shaders
Between pixel and vertex shaders
Between pixel shaders and hardware
Between shader fragments
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Integrating with
Applications
• Extract dissassembly and use as .asm
•
shader code ala DX8
Use compiled shader object
• Enables constant table access
• Via ID3DXConstantTable Interface
• Use in an effect object
• Manage constants, fallbacks, etc.
• Via ID3DXEffect Interface
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Language API:
Standalone
• Compiler returns a VS or PS and a
symbol table
• Maps extern constants to registers
• Any expression of constants (i.e. per
•
primitive expressions) still performed
per vertex
Symbol table is a set of constants
• ID3DXConstantTable interface
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ID3DXConstantTable
• Exposes constant parameter
metadata
• For convenient specification of shader
input data
• SetMatrix( “curv”, matrix );
• String or handle
• D3DXHandle *hHandle
• SetVector()
• SetValue()
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Shader Management
• Due to varying effects desired:
• Diffuse, ambient, or specular terms
• Skinning on or off, number of lights
• Due to different hardware generations
• DirectX® 8, 9, 9.1
• Apps must manage a combinatoric
•
number of shaders
FF pipeline does not have these issues
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Solution: “Effects”
• D3DX Effect Framework
• Routines to load and select shaders
• Originally developed to manage
•
multitexture shaders in DirectX 6
Now fully integrated with the HLSL
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Effect Framework
• Encapsulation of device state
• Enables scalable rendering
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•
techniques
Allows controlled fallback
Can’t just switch to multi-pass
• Older hardware can’t do more passes
since fill rate is less
• Helps rapid prototyping
• Runtime interpretation of text-based
effect definition
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Effect Framework Goals
• Standard way of representing shading
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•
algorithms
Ease of authoring
Enable some abstraction between author of
effect and user of the effect
• Facilitates sharing of effects
• Enables effect – geometry optimizations to be
done at author-time, install-time, load-time or
runtime
• Cross Platform
• Efficient for runtime use
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Effect Model
Effect Water
Technique DX9
pass0
pass1
Technique DX8
pass0
Technique DX7
pass0
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Effect Framework
Fallback Techniques
• Techniques are grouped by their
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•
•
quality or “LOD”
Techniques can be chosen based on
what hardware creates successfully
Can test performance in back buffer
User responsible for drawing
geometry
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Parameterized Effects
• Effects can have parameters
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of various types
Parameters augment static
state description in the .fx files
How (and which) parameters get
used defined by the effect
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Parameterized Effects
• Shared parameters (aka Globals)
• Shared across multiple effects
• Tagged in effect file as shared
• User selects the list of effects whose shared
parameters are linked at runtime
• Setting once updates all linked effects
• Naming convention for artist tweakable
• Enables hooking UI to specific parameters
• .X file reference for the same
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Design for Runtime
Efficiency
• Compile effects into hardware
•
friendly format
• State blocks and push buffers
Efficient setting of effect parameters
• Can set parameters within effect
application
• Integration with an optimizing
language back end
• Caching common parameter combinations
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Unify Fixed and
Programmable Pipelines
• A consistent framework for
programming shaders
• Fixed-function programming using render
states, texture stage state, fixed-function
vertex processing
• Assembly level vertex and pixel shader
programming
• Shading language based programming
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Unify Cross-Platform
Programming
• Techniques in an effect can span
•
shader models (like VS 1.1, VS 2.0,
etc.)
Unified parser allows handling the
same effect file cross platform
• Only techniques that validate on runtime
platform available for actual use
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Effect-Language
Integration
• Techniques can call language functions
• This is where the back-end is specified
• Same function can be used in multiple techniques
compiled to multiple back-ends
• Expressions of parameters can be used in
•
state assignment
Per-primitive expressions detected and
optimized out by compiler when within an
effect
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Specialization
• Specify constants that are to be
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literals
via ID3DXEffectCompiler Interface
Call CompileEffect() method
• returns pre-optimized shader
Easily generate multiple shaders
optimized for specific cases
Can helps shader management by
generating them on the fly
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Linking Effects with
Geometry
• .X file extensions to link effect with
geometry
• Enhance the notion of materials to include effect
files
• Inline or external references
• Besides referencing effects, certain parameter
values can be specialized in EffectInstance
• This is usually the artist tweakable ones
• D3DX API support for associating effects
with meshes
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Fragment Linker
• Efficiently links together
• HLL fragments
• And asm fragments
• Current Features:
• Symbol table resolution
• Register use optimization
• Dead code removal
• via ID3DXFragmentLinker interface
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Performance
• Compiler updates will be frequent
• Microsoft has good compiler people
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Current Back Ends
• Vertex Shader 1.1, 2.0
• Pixel Shader 1.1, 1.4, 2.0
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Summary
• HLSL abstraction solve
• Continuing hardware evolution
• Shader programming complexity
• API semantics solve
• Shader interoperability
• D3DX Effects, specializers solve
• Combinatoric numbers of shaders
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Summary
• HLSL is the next step in graphics
•
API/hardware evolution
DirectX implementation provides
• Close API integration
• Semantic binding to low-level API
• Shader management via D3DX effects
• Full IDE support including debugging
• Performant cross vendor support
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Action Items
• Check it out!
• Use it in your research &development
• Let us know what you think
• directx@microsoft.com
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Questions
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Backup
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Unique Features
• Cleanly integrated with Direct3D API
• Run-time compilable
• Integrated with Effect Framework
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API Integration
• Co-designed with DirectX 9 API
• Enables ease-of-use in apps and in
•
tools
Enables improved performance
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Run-Time Compilable
• Enables CPU to construct and
•
optimize shaders for GPU dynamically
Facilitates authoring tool/art pipeline
• Enables dynamic content/titles
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