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Chapter 2

- Graphics Programming
- 24 Jan 20067

Sierpinski Gasket

- pre-Mandelbrot classic
- found by W. Sierpinski around World War I.
- generated by recursivly dividing a triangle into four congruent smaller triangles

- think of the interior triangles as "holes”
- they occupy more and more of the total area, while the "solid" portion becomes as hopelessly fragile

Pseudocode

1. Pick a point at random inside the triangle

2. Select one of the three vertices at random

3. Find a point halfway between the initial point and the randomly selected vertex

4. Display this new point by putting some sort of marker, such as a small circle, at its location

5. Replace the initial point with this new point

6. Return to step 2

Pen Plotter

- moveto(x,y)
- lineto(x,y)

Problems with Pen-Plotter model

- 3D difficult
- must convert 3d world to 2d projection explicitly

- OpenGL allows us to focus on building 3D world and let computer handle projections

Display funtion

Check programs online - lectures/chapter1/lab, boat

Coordinate System in OpenGL

- What units are x, y, and z?
- your choice
- device independent
- world coordinate system

- Before displaying on output device, world coordinates must be converted to device or raster or screen coordinates

POINT TO REMEMBER

- We are studying computer graphics
- We are not studying OpenGL
- won’t cover all functions in OpenGL

Graphics System as a Black Box

Function Calls

Output

User

Program

Graphics

System

Input/Output

Devices

Data

Input

API Functions

- Primitive Functions
- Attribute Functions
- Viewing Functions
- Transformation Functions
- Input Functions
- Control Functions

OpenGL - What is it?

- A graphics rendering library
- API to produce high-quality, color images from geometric and raster primitives
- Window System and Operating System independent
- OpenGL “doesn’t do windows”

OpenGL

- Most widely adopted graphics standard
- Introduced in 1992
- High visual quality and performance
- Industry standard
- Stable
- Reliable and portable
- Evolving
- Scalable.
- Easy to use.
- Well-documented.

Related APIs

- GLU (OpenGL Utility Library)
- guaranteed to be available
- tesselators
- quadrics
- NURBs, etc.
- some surprisingly common operations, such as projection transformations (such as gluPerspective)

- guaranteed to be available

Related APIs

- GLX or WGL
- bridge between window system and OpenGL

- GLUT
- portable bridge between window system and OpenGL
- not “standard”, but uniformly popular

Homework

- Read Chapter 3
- Assignment 2 - Program due 01/31/2007
- Display your scene in 3D. Use at least 5 different graphics primitives.

glOrtho (GLdouble left, GLdouble right, GLdouble, bottom, GLdouble top, GLdouble near, GLdouble far)

- Creates a viewing volume with a box shape.
- Direction of projection is parallel to z axis.
- Viewpoint faces -z axis.
- glOrtho (0.0, (GLdouble) w, 0.0, (GLdouble) h, -500.0, 500.0);

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