1. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 CS5500 Computer Graphics April 19, 2007

2. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Today’s Topic Overview of 3D pipelines. Scope of the next 2 or 3 assignments.

3. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Many Views of Graphics Pipeline Simple “Front-End/Back-End” view. Textbook version in [Foley/van Dam]. David Kirk’s (nVidia CTO) version presented in EG Hardware Workshop 1998: (slide 05) http://www.merl.com/hwws98/presentati ons/kirk/index.htm http://www.merl.com/hwws98/presentati ons/kirk/index.htm

4. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Simplified View The Data Flow: 3D Polygons (+Colors, Lights, Normals, Texture Coordinates…etc.)  2D Polygons  2D Pixels (I.e., Output Images) Transform (& Lighting) Rasterization

5. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 A Quick Review By default, graphic pipeline will do the following: 1)Take as input various per-vertex quantities (color, light source, eye point, texture coordinates, etc.) 2)Calculate a final color for each vertex using a basic lighting model (OpenGL uses Phong lighting) 3)For each pixel, linearly interpolate the three surrounding vertex colors to shade the pixel (OpenGL uses Gouraud shading) 4)Write the pixel color value to the frame buffer

6. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 The View of DirectX 8 (Note: This figure is overly crowded, so don’t worry about it if you can’t understand it at the first look. The next slide might give you a better idea of the pipeline.)

7. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007

8. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 And a really scary one…

9. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007

10. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 The next 6 slides are borrowed from UNC-CH COMP236 Course Slides (Spring 2003) http://www.unc.edu/courses/2003spring/ comp/236/001/handouts.html http://www.unc.edu/courses/2003spring/ comp/236/001/handouts.html

11. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007

12. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007

13. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007

14. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007

15. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007

16. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007

17. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007

18. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Implementing a 3D Pipeline A case study -- MESA. Mesa 3D Graphics Library –A famous open source effort to implement OpenGL. –Pure software implementation, meaning all computation is done on CPU, not on GPU. –Used to call MesaGL, but SGI complained about it due to customer support issues.

19. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Two Different Approaches Consider how you expect the users to create the contents to your 3D pipeline. Method 1: by providing 3D model files (e.g., in the OBJ or VRML format) –Our approach since it’s easier to implement. Method 2: by writing an OpenGL program. –MESA’s approach.

20. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 OpenGLDrivers OpenGL commands 3D Renderer 3D Models CPU & GPU MESA

21. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Input File Format Very similar to an OpenGL “command stream,” for example: Rotate angle, x, y, z Translate x, y, z Color R, G, B, A Begin Triangle Vertex x, y, z... End...

22. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Major Components Data structures for: –Points, vectors, matrices –Lines and polygons (or just triangles) –Frame buffer and textures Transformation Lighting Clipping & Projection Rasterization & texture mapping

23. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Don’t Reinvent the Wheel A few useful 3D vector and matrix code: http://www.cs.nthu.edu.tw/~chunfa/code /algebra3.zip http://www.cs.nthu.edu.tw/~chunfa/code /algebra3.zip Or borrow one from your friends, or find a good one from the Internet.

24. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Graphics Hardware Why do we study the graphics pipeline in such depth? Why not teaching more Cg or shader programming? You’ve got to know some hardware! They are all built upon the traditional 3D pipeline.

25. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Why Need Hardware All parts of graphics pipeline can be done in software. –But very slowly. –Example: mesaGL For some applications, speed is beauty –Games –Walkthrough –Visualization

26. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Evolutions of Graphics Hardware 1.Gouraud-shaded polygons. 2.Then came antialiasing. 3.Then came texture mapping. 4.Now comes programmable shading.

27. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 John Poulton’s Chart

28. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Fixed vs. Programmable Starting in 1999 some graphics cards used the standard lighting model and Gouraud shading to draw polygon fragments entirely in hardware Implementing the pipeline in hardware made processing polygons much faster, but the developer could not modify the pipeline (hence “ fixed function pipeline ” ) New programmable hardware allows programmers to write vertex and pixel programs to change the pipeline

29. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 OpenGL Fixed Function Vertex Transform [MVP],[MV],[MV] -T Lighting [0,1] [0,1] Texgen Texture Matrixn Color SecondaryColor TexCoordn EdgeFlag Normal Vertex (object) TexCoordn EdgeFlag Vertex (eye) Vertex (clip) Front&Back Color Front&Back SecondaryColor

30. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 GL2 Vertex Processor Temporaries Vertex Shader Uniform Color SecondaryColor TexCoordn EdgeFlag Normal Vertex (object) TexCoordn EdgeFlag Vertex (eye) Vertex (clip) Front&Back Color Front&Back SecondaryColor

31. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Programmable Shaders A concept made popular by Pixar’s RenderMan. First appeared in hardware: UNC PixelFlow –See SIGGRAPH papers by Molnar 1995 and Olano 1997. Made affordable by nVidia GeForce3 and XBox.

32. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Faked Global Illumination Shadow, Reflection, BRDF…etc. In theory, real global illumination is not possible in current graphics pipeline: –Conceptually a loop of individual polygons. –No interaction between polygons. Can this be changed by multi-pass rendering?

33. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Future Trends Vertex/Pixel shaders will become more and more flexible –Less limits on program size –Able to execute branch instructions –Capable of moving complicated effects (like those in Renderman) onto the GPU More and more operations executed per-pixel rather than per-vertex As people get more creative with the hardware we will see more techniques for non-photorealistic rendering

34. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Future Trends Real-time fur

35. CS5500 Computer Graphics © Chun-Fa Chang, Spring 2007 Future Trends More realistic skin –Subsurface scattering approximation