D3DX High Level Language and Effects

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D3DX High Level Language and Effects

• Anuj Gosalia
• Development Lead
• DirectX Graphics
• Microsoft Corporation

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Design Goals

• High level enough to hide hardware specific
  details
• Simple enough for efficient code generation
• Familiar enough to reduce learning curve
• Based on C-like syntax
• Provide enough optimizing back-ends for
  portability

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Back Ends

• Vertex Shader 1.0, 1.1, 2.0
• Pixel Shader 2.0
• Maybe even 1.x
• X86, etc
• Useful for vertex programs and per-primitive
  expressions
• Authoring tool languages?
• Or have them use DirectX based renderer

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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

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Type Casts

• Float can be promoted to any type by replicating
  the float as necessary
• (v 0.5 0.5) instead of
• (v vec3(0.5, 0.5, 0.5) vec3(0.5, 0.5, 0.5))
• Vectors can be down-cast
• Left prefix
• Matrices can be down-cast
• Upper left subset

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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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VS input semantics

• positionn
• blendweightn
• blendindicesn
• normaln
• psizen
• diffusen
• specularn
• texcoordn
• tangentn
• binormaln

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VS output / PS input semantics

• position
• psize
• fog
• colorn
• texcoordn

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Operators

• Pretty much all of C operators
• Incl ?, sizeof and comma(,)
• No new semantics
• Despite temptation
• 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

• statements
• expression
• return expression
• if ( expression ) statement else statement
• for ( expression variable_declaration
  expression expression ) statement

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Functions

• Standard C like functions
• Output type and input parameters
• Parameters can be passed by value or reference
  (C style syntax)
• Externally referenced function must have
  semantics associated with parameters
• Needed for future versions of DirectX
• Inlined internally. No recursion

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Functions (cont.)

• Can be static (not externally accessible)
• Non-static functions parameters must have
  Direct3D declarator semantics
• Parameters can be marked const
• Parameters can have default initializers

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Intrinsic functions
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Difference from C

• No pointers
• No recursion

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Preprocessor

• define
• elif
• else
• endif
• error
• Function-style defines not supported

• if
• include
• line
• undef

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Language API Standalone

• Compiler returns a VS or PS
• And a symbol table
• map extern constants to registers
• Any expression of constants (i.e. per primitive
  expressions) still performed per vertex

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Language API Effect Framework

• Use effect parameters
• Per primitive expressions of parameters computed
  outside the vertex shader

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Effect Framework

• Encapsulation of device state
• Enables scalable rendering techniques
• Allows controlled fallback
• Cant just switch to multi-pass
• Older hardware cant do more passes since alpha
  blending 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 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 FrameworkFallback Techniques

• Uses controlled effect fallbacksEffect
• Technique
• Pass
• Implementation
• Simple text file (.fx) to define effects

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Effect FrameworkFallback Techniques

• Techniques are grouped by their 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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Effect Data types

• DWORD, FLOAT
• VECTOR, MATRIX
• TEXTURE
• VERTEXSHADER, PIXELSHADER
• STRING
• Enables user-data associated with effects
• Not used to program device state

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Parameterized Effects

• Effects can have parameters 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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Example
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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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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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Reconciling Geometry Layout

• DirectX 8 VS assume geometry layout
• Decl VS code tied together
• Forces shader author to communicate with geometry
  provider
• Standard register conventions can help some
• DirectX will decouple decl from VS
• Both decl and VS refer to semantics rather than
  register names
• Direct3D runtime will connect appropriate vertex
  stream data to VS registers

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Vertex Component Semantics

• VertexDecl now has usage field
• Position, Normal, Tangent, Binormal, etc.
• Connect shaders to geometry
• No need for a register convention
• Accommodates more semantics than limited by
  register count
• Any shader to any geometry
• Well almost
• Semantics were needed for fixed-function pipe

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DX8 Vertex Declaration
Strm0
Strm1
Vertex layout
v0
skip
v1
Declaration
vs 1.1 mov r0, v0
Shader handle
Shader program
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New Vertex Declaration
Strm0
Strm1
Vertex layout
pos
norm
diff
Declaration
vs 1.1 dcl_position v0 dcl_diffuse v1 mov r0,
v0
Shader program (Shader handle)
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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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Example VertexDecl

• D3DFVF_POSITION D3DFVF_DIFFUSE
  D3DFVF_SPECULAR D3DFVF_TEX1
• D3DVERTEXELEMENT9 ve 0,  0,TYPE_FLOAT3,
  METHOD_DEFAULT, USAGE_POSITION,0, 0, 12,
  TYPE_D3DCOLOR, METHOD_DEFAULT,
  USAGE_DIFFUSE,0, 0, 16, TYPE_D3DCOLOR,
  METHOD_DEFAULT, USAGE_SPECULAR,0, 0, 20,
  TYPE_FLOAT2, METHOD_DEFAULT, USAGE_TEXCOORD,0,
   D3DDECL_END()

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Example Vertex Shader

• vs.2.0
• dcl_dmap v0
• dcl_position v1
• dcl_normal v2
• dcl_blendweight v3
• def c0 1.,1.,1.,1 // white
• add oT0, v2, r1

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Call to Action

• Give feedback of language design
• We would like to work with you
• Help create a consistent standard
• Play with prototype
• When we actually give you one
• Integrate it with your tools

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Questions?