1. Digital Media Lecture 8: Vector Graphics 3D Georgia Gwinnett College School of Science and Technology Dr. Jim Rowan

2. Refer to Supplemental text:

3. 3D X & Y like 2D graphics Z is Height (or depth)

4. 3D 3D shapes (objects) are defined by their surfaces Complicated because a 3D object (inside the computer) must be translated into 2D to be viewed… And you need to: –specify the viewpoint, a camera –specify the lighting

5. 3D Specifying the camera and the lighting has one huge advantage over 2D –Automatically generates all of shadows BUT… rendering (converting 3D to 2D) is extremely computationally expensive (demanding, time consuming) –It can be slow!

6. 3D Lighting has different characteristics and must be specified –natural or artificial –spot or flood –color –multiple sources –reflections off other objects in the scene Atmosphere must be intentionally included Surface texture must be specified

7. Issues of focus/atmosphere Examples from Sintel Sintel Example

8. Managing Complexity

9. Structural hierarchy Things in the real world are compositions of smaller things Things in the 3-D graphics world are also compositions of smaller things Hierarchical structure is an excellent way of coping with complexity Also seen in object-oriented programming like Java and Squeak!

13. 3D Models

14. So… How do you build a model inside a computer when you can’t touch it? Constructive Solid Geometry Free Form: Bezier Surfaces Free Form: Extrusion Procedural modeling

15. 3D models Constructive solid geometry –building things from known shapes –uses geometric solids: cube, cylinder, sphere and pyramid –objects build by squishing and stretching those objects –objects joined using union, intersection and difference

16. Intersection

17. Difference

18. Union or just two objects?

19. Free Form Building things one side at a time Uses an object’s surface (it’s boundary with the world) to define it Build surfaces from flat polygons or curved patches –flat polygons are easier to render and therefore frequently used in games where computational power is limited Results in an object drawn as a “mesh” Can be done using Bezier surface patch but they have 16 control points! More tractable (do-able) patch uses a surface called a non-rational B-spline

20. Free Form: Extrusion Building things using a play-doh factory Move a 2 dimensional shape through space along a line The line can be straight or curved

21. Procedural modeling Best known is based on Fractals –Fractals –exhibit the same structure at all levels of detail aka “self similar” –used to model natural objects Particle systems... many particles, few controls –Fur, hair, grass… Physics... distribution of mass, elasticity, optical properties, laws of motion

22. 3D Rendering Rendering engine handles the complexity Wire frames are used to preview objects and their position –can’t tell which surface is closer to us and which surface is hidden To save computation time, hidden surfaces are removed before rendering –Why render what can’t be seen?

23. 3D rendering Lighting –Added to scene much like an object –spot light, point source, floodlight... –position and intensity Direct relationship between rendering quality and computational burden(render time)

24. Render time video illustration http://www.youtube.com/watch?v=jtWPW8yJtgM&feature=channel_vi deo_title