1. Dr. Jim Rowan ITEC 2110 Vector Graphics II
Digital Media
Dr. Jim Rowan
ITEC 2110
Vector Graphics II

2. Manipulating objects AKA closed curves
Translation is a simple up/down side-to-side movement
Scaling: make bigger or smaller
Rotation about a point
Reflection about a line

3. Object fills
Solid color
Patterns
Gradients
linear
radial

4. 3-D... 3 dimensions x, y and z x & y form the ground plane
z is the height

5. 3-D Way more complex than 2-D
3-D shapes (objects) are defined by their surfaces
Made even more complicated by the fact that a 3-D object inside the computer must be translated into 2-D to be rendered on a computer screen...
This results in the need to specify the viewpoint

6. 3-D: additional complexity
lighting
natural
artificial
atmosphere
surface texture
rendering is extremely computationally expensive (demanding)

7. Managing Complexity

8. 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!

9. Structural hierarchy Car Wheels (4) Doors (2) Lights tire wheel hubcap
handles
inside
lever
outside
button
handle
window(s)
Lights
headlights (2)
tail lights (2+)
stop lights (2+)

10. 3-D: additional complexity
rendering is extremely computationally expensive (demanding)
lighting
natural
artificial
reflections off other objects in the scene
shadows cast by other objects in the scene
surface texture affects appearance

11. 3D Models

12. 3-D models Constructive solid geometry
uses geometric solids: cube, cylinder, sphere and pyramid
objects build by squishing and stretching those objects
objects joined using union, intersection and difference

13. 3-D models constructive solid geometry
Union
new object is made from the space occupied by both objects
Intersection
new object is made of the space that the two objects have in common
Difference
new object is made from

14. 3-D models Free Form
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 have 16 control points
More tractable patch uses a surface called a non-rational B-spline

15. 3-D models Free Form: Extrusion
Draw a 2 dimensional shape through space along a line
The line can be straight or curved

16. 3-D models Procedural modeling
Objects are defined by formulas
Best known is based on Fractals
Fractals
exhibit the same structure at all levels of detail
aka “self similar”
used to model natural objects
Meatballs model soft objects
Particle systems... many particles, few controls
Physics... distribution of mass, elasticity, optical properties, laws of motion

17. 3-D 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

18. 3-D 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

19. 3-D rendering Shading... how light reacts with surface
Based roughly on physics but modified by heuristics
Texture mapping
An image is mathematically wrapped around the object
Light reflecting off objects of one color affect the color and lighting of surrounding objects
Two methods
Ray tracing Complex... must be repeated for pixel in the image... photo-realistic results
Radiosity

20. Questions?