OpenGL

1. OpenGL Overview and applications Yasir O. Sinada Olivier Steiger

2. Historical background and characteristics • OpenGL (“Graphics Library”) was introduced in 1992 by Silicon Graphics • Based on older IRIS GL • Specifications governed by the OpenGL Architecture review board • (Compaq, Evans & Sutherland, Hewlett-Packard, IBM, Intel, Intergraph, Microsoft, and Silicon Graphics) • Current version: 1.2 • Characteristics: • Platform independent: can run on consumer electronics, PC’s, workstations, etc. • Backward compatibility required in new versions • Supported by many hardware accelerators => fast

3. Fig.: Processing pipeline Architecture and terminology • Model: whatever we want to render; a model is made up of primitives • Polygon: closed, flat surface bounded by at least 3 line segments. Basic building block in OpenGL • Vertex: corner of a polygon. Polygons are defined by their vertices (coordinates: x, y, z, w) • Matrix transformations: allows to scale, rotate and translate vertices • Modelview matrix: turns the raw model coordinates into coordinates as viewed from viewpoint • Projection matrix: clips out vertices that are out of the specified viewing volume • Perspective division: generates the normalized device coordinates using w. Usually, w=1 • Viewport transformation: 3D coordinates are turned into 2D framebuffer coordinates (=rasterization) • Rendering: turns the model into a shaded, textured and illuminated scene

4. The ten OpenGL primitive types All objects have to be made up out of these ten primitives!

5. Programming syntax: an example Source code

6. Projector Real world Application: medical sciences • Virtual endoscopy: internal examination of human body without surgery • => painless teaching of endoscopy • Augmented reality: combine real image with overlaid graphics • => guiding of knife or needle during brain surgery • => overlay of ultrasonic 3D scan and patient • Surgical simulation: • => data glove and head-mounted display allow • training of difficult processes without risk • Finite element simulation of heart defibrillation: • => allows to optimize the size and locations of the needed electrodes as well • as magnitude of defibrillation shocks

7. Application: medical sciences (II) • Advantages: • Avoids unnecessary interventions • No need for patients (rare diseases) • Assistance for difficult procedures • Problems: • Applications need to run in real time (10-15 frames/sec), BUT: • the model for simulation of heart defibrillation is composed of more than 1.5 million tetrahedral • elements with 250000 degrees of freedom => 4 billion floating-point ops for solution • Resolution needed for diagnostics: 2000x2000 pixels => data sets have sizes about 13.4 GByte

8. Application: geology / mining • The use of 3-dimensional models allows • Intuitive visualization of big data sets (measures) • Impact simulation before construction

9. Application: industrial design • Visualization of not yet realized prototypes, which can be located in their future context • => potential clients get a better opinion of the product, can give feedback • Behavior visualization: thermal graphs of airplanes, pressure distribution in mechanical structures, … • => weak points are easily located and optimizations can be tested on virtual model

10. Application: special effects • Used in motion pictures, advertisement, video games and TV industry. • Today, this is the biggest application field for 3D graphics! • Distinguish between “realistic” 3D (Jurassic park) and “Virtual-3D” (A bug’s life)

11. Application: special effects (II) The high resolution and frame rate (especially for movies) requires powerful equipment => High cost for FX Compositing is also more used than in other fields => many difficulties due to synchronization, color correction, realistic texturing, …

12. OpenGL future • Language improvements: • often used extensions (fog coordinates, shared texture color palette, point parameters, …) • will get included into core OpenGL • sequences of small functions get grouped into more powerful extensions • Hardware evolution: • as hardware gets cheaper, many software functions will be included into hardware • => speed improvement • standard video boards support OpenGL (motivated primarily by the game industry…) • New application: • data compression (MPEG-4) • “Virtual reality” (3D navigation)

13. More information? - Ron Fosner. “OpenGL. Programming for Windows 95 and NT.” Addison-Wesley developpers press, 1998 - www.opengl.org: general OpenGL site - www.sgi.com/software/opengl: some information, a lot of advertisement - Soferman, Blythe and John. “Advanced Graphics Behind Medical Virtual Reality: Evolution of Algorithms, Hardware and Software Interfaces.” Proceedings of the IEEE, vol. 86, No. 3, March 1998

14. Class questions • Why does OperGL provide only 10 primitives? • The conception of OpenGL goes back to 1992, when machines were slow and hardware extensions • expensive. Silicon Graphics wanted to provide a graphical language which allows the creation of any • kind of objects without requiring a too big computational amount; however, the goal was not a language • for the efficient creation of graphical objects (circles, cubes, …), which can be realized with other • software, but for scenes with lights, textures and animations. • In order to do so, they brought up ten fundamental shapes, or primitives, and associated them with many • powerful lightning and matrix operations. The primitives are just the “fundamental alphabet” allowing • the creation of complicated scenery with simple objects. More primitives would result in an increased • language complexity, slowing down the computation in certain cases.