Even more jobs Spring Career Fair Shading Architectures Fair - PDF document

Even more jobs  Spring Career Fair Shading Architectures  Fair  Wednesday, March 28th  11am - 4pm  Gordon Field House  Interviews  Thursday, March 29th  www.rit.edu/recruit Plan Shader Architectures  Today  RenderMan  Shader Architectures  Cg  Next Week  Shader Language Specifics  How they are alike  Tuesday: Lecture  How they are different  Thursday: Lab Shader System RenderMan  Common traits:  Renderman consists of three parts:  Functional scene description mechanism (API for  Scene separate from shader C) Renderman is an Interface!  “load” a “compiled” shader  State Model Description – Maintains a current graphics  Parameter passing between scene and shader state that can be placed onto a stack.  Global “graphics state” variables  Geometry is drawn by utilizing the current graphics state.  File format - Renderman Interface Bytestream  Shader programs components of rendering (RIB) pipeline.  Shading Language and Compiler.  https://renderman.pixar.com/products/rispec/index.htm 1

Rendering using RenderMan Runtime architecture 3D Scene Shader 1 Shader Shader / render link Description “object” RenderMan file Shader 2 slc (RIB) Renderer Shader Shaders Shader 3 “object” (prman) Graphics file state (compiled shader code) Shader “object” file Texture Map Rendering application Renderman Shading Language Renderman Shading Language  Renderman Shading Language  Unlike other shading languages, RenderMan allows for procedural definition of all types of light transport,  Inspired by Cook’s shade trees not just reflection  Goals  Light emission  Atmospheric effects  Abstract shading language based on ray optics,  Reflection independent of any specific algorithm or  Transmission implementation  Transformations  Interface between rendering program and  Bump Mapping shading model  High level language that is easy to use. Renderman Shading Language Renderman Shading Language  Types of shaders  Types of Shaders  Light source shaders - calculates the color of  Displacement Shaders - perturb the surface of a light being emitted in given direction. an object  Surface reflectance shaders - computes the  Imager Shader - post processing on image light reflected from a surface in a given pixels. direction  Volume shaders - implements the effect of light passing through a volume of space, i.e., exterior, interior and atmospheric scattering effects. 2

Renderman Shading Language RenderMan scene  RenderMan assumes a basic “graphics state”  Dataflow Model scene model  Scene hooks into shader  Achieved via predefined “global” variables  Result of shader  Achived by setting other predefined “global” variables.  Shaders programmed independently from other shaders [ Renderman Companion , 277] Renderman Shading Language Renderman Shading Language Attaching shaders to object  Dataflow Model  RiLightHandle RiLightSource (“name”, parameterlist); or LightHandle LightSource “name” parameterlist - sets shader “name” to be the current light source shader  RiSurface (“name”, parameterlist); or Surface “name” parameterlist - sets shader “name” to be the current surface shader. RiAtmosphere (“name”, parameterlist); or  Atmosphere “name” parameterlist - sets shader “name” to be the current atmosphere shader. [ Renderman Companion , 277] Light Shaders Light Shaders  Define color and intensity of light in a given direction  Light is “collected” by other shaders not “emitted” by light source shader  Light shaders define “potential” light that can be collected later. [ Renderman Companion , 277] 3

Surface Shaders Light Shaders [Renderman Companion , 277] Surface Shaders Illumination Models  Defines color/opacity at a surface point  Can query defined light sources  Approaches  Illumination Model  Image Textures  Procedural Textures  Bump Mapping Image Texture Mapping Environment Mapping 4

Procedural Textures Procedural Texture Different plain Grooved grain Different colors mortar colored within bricks bricks Olano, 1998, http://www.cs.unc.edu/~olano/papers/dissertation/ Displacement Shaders Displacement Shaders  Used to perturb normal to give appearance of wrinkles  Basic bump mapping  Applied before surface shader [Renderman Companion , 277] Volume shaders Displacement Shader [Renderman Companion,277] 5

Volume Shader Volume shader  Defines change of color/opacity of light going through a volume  Fog, smoke, fire, haze Imager Shader Imager Shader  Allows for postprocessing of final rendered image  Applied pixel-by-pixel  Tone reproduction  Non-photorealistic rendering  Supported in prman? [ Renderman Companion , 277] Imager Shader Shader order in prman  Displacement Shader  Surface Shader  Queries light shaders  Volume Shaders  Imager Shader  prman creates bytecode for SIMD virtual machine for compiled shaders 6

Summary -- RenderMan Real-time Shading  Interface -- not a renderer  Linked to hardware  Independent of actual implementation  RenderMan == GOOD  Scene / Shader separation  Can it be done on the graphics card?  Shaders define interactions of light &  Assembler geometry modification  Higher level language  Light / Surface / Displacement / Volume / Imager  break Real time vs Off-line shading Graphics Hardware Pipeline  Interactivity  Viewpoints will change  Performance is critical  Frame to frame  Execute on GPUs  Restrictions  Memory  Registers  Texture units and memory  Data type accuracy Graphics Hardware Pipeline Graphics Hardware Pipeline  Vertices  define geometrical primitives  Position in 3D space  Color / text coords / materials / etc.  Fragments  “pixel state” -- Correspond to pixels  3D -> 2D  Projection  Scan conversion 7

Shading applets Programmable Graphics Pipeline  Gouraud:  http://www.vidimce.org/college/school/cs4 413.f96/program.6/ GPU Assembler Programmable Graphics Pipeline  Vertex processor  Operates on vertices  Vertex shaders  Fragment processor  Operates on fragments  Fragment / Pixel shader Cg Environment Cg Enviornment  Cg == “C for Graphics”  Cg Compilation  Proceed with caution.  Indirect link to GPU  Standard APIs  Compiles to interface with OpenGL or Direct3D layer  Layer of standardization / abstraction from  OpenGL/DirectX will command the GPU graphics card (GPU)  CGRuntime  OpenGL  Direct3D 8

Cg Environment CgFX  Putting it all together  File format for encapsulating complete render state for an effect  Allows for “packaging of effects”  Loading of effects in external applications.  Maya  3D Studio Max  SoftImage CgFX Some realtime demos So what, you say Unintended effects  GPUs are good processors in their own  nVidia videos right  Programming non-graphical apps on GPUs  Image Processing  Numerical Computation  Animation  Data Mining 9

Cg Summary Next week  Platform / Hardware independent  Lecture: Language nuts and bolts language  Lab: RenderMan / Cg “Hello World”  Scene / Shader separation  Shaders Linked to hardware  Only fragment and vertex shaders  Questions 10