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Computer Graphics (fall 2009)

Computer Graphics (fall 2009). School of Computer Science University of Seoul. OpenGL Graphics System. 3D Graphics API. OpenGL Microsoft Direct3D Implemented in DirectX Supports MS Windows only ( cf : Cedega ) RISpec ( RenderMan Interface Specification)

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Computer Graphics (fall 2009)

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  1. Computer Graphics(fall 2009) School of Computer Science University of Seoul

  2. OpenGL Graphics System

  3. 3D Graphics API • OpenGL • Microsoft Direct3D • Implemented in DirectX • Supports MS Windows only (cf: Cedega) • RISpec (RenderMan Interface Specification) • Developed by Pixar Animation Studios • Off-line rendering • Java3D • Scene graph based • Runs on top of OpenGL or Direct3D.

  4. What Do We Need To Render A 3D Scene? • Objects • A Viewer (Camera) • Light Sources • Material Properties(of Objects) [image courtesy of http://www.yourdictionary.com/computer/3-d-graphics]

  5. Simplifications for Interactive Rendering • Objects • Composed of primitives (points, lines, triangles,…) • A Viewer (Camera) • Two types (orthogonal & perspective) • Light Sources • Simple lights (directional and positional) • Gouraud shading model • Material Properties (of Objects) • Phong reflection model

  6. How To Render A Triangle • For each vertex • Transforms it according to the current setting • Computes its color based on the material property and lights • Assembles three vertices into a triangle • Rasterizes the triangle • For each pixel • Assigns its color by interpolating the color of vertices [image courtesy of nVidia]

  7. OpenGL • “…standard specification defining a cross-language, cross-platform API for writing applications that produce 2D and 3D computer graphics.” (Wikipedia) • Specifies common interface independent of graphics hardware.  Hardware vendors need to provide drivers. • Cross-platform

  8. OpenGL (cont’d) • Rendering feature only • No UI, window control, file I/O, etc… • Additional library (e.g., GLUT) required for a complete program. • Immediate mode • State machine • Pipeline architecture • Low level operations only

  9. Hardware Independent • Hardware-specific OpenGL drivers need to be installed. • nVIDIA • AMD (ATI) • Intel • Some features are supported by S/W not H/W.

  10. Cross-platform • Requires a layer between the OpenGL and the window system • GLX: for X Window System • WGL: for Microsoft Windows • AGL (Apple Graphics Library): for MacOS

  11. Rendering Only • Requires additional library for UI, windows management, etc. • Win32 API • GLUT (OpenGL Utility Toolkit) • Qt • wxWidgets

  12. Graphics Pipeline • For better throughput! [image courtesy of Wikipedia]

  13. The Design of OpenGL • Recommended reading: “The Design of the OpenGL Graphics Interface” (1994, Mark Segal and Kurt Akeley)

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