Graphics Programming

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Chapter 2

• Graphics Programming
• 24 Jan 20067

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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

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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

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Pen Plotter

• moveto(x,y)
• lineto(x,y)

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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

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Display funtion

• Check programs online - lectures/chapter1/lab,
  boat

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Coordinate System
3D COORDINATE SYSTEMS
Y
Y
Z
X
X
LEFT HANDED
RIGHT HANDED
Z
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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

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POINT TO REMEMBER

• We are studying computer graphics
• We are not studying OpenGL
• wont cover all functions in OpenGL

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Graphics System as a Black Box
Function Calls
Output
User Program
Graphics System
Input/Output Devices
Data
Input
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API Functions

• Primitive Functions
• Attribute Functions
• Viewing Functions
• Transformation Functions
• Input Functions
• Control Functions

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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 doesnt do windows

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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.

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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)

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Related APIs

• GLX or WGL
• bridge between window system and OpenGL
• GLUT
• portable bridge between window system and OpenGL
• not standard, but uniformly popular

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Homework

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

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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)